1
|
André T, van Berkel AA, Singh G, Abualrous ET, Diwan GD, Schmenger T, Braun L, Malsam J, Toonen RF, Freund C, Russell RB, Verhage M, Söllner TH. Reduced Protein Stability of 11 Pathogenic Missense STXBP1/MUNC18-1 Variants and Improved Disease Prediction. Biol Psychiatry 2024; 96:125-136. [PMID: 38490366 DOI: 10.1016/j.biopsych.2024.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 03/04/2024] [Accepted: 03/05/2024] [Indexed: 03/17/2024]
Abstract
BACKGROUND Pathogenic variants in STXBP1/MUNC18-1 cause severe encephalopathies that are among the most common in genetic neurodevelopmental disorders. Different molecular disease mechanisms have been proposed, and pathogenicity prediction is limited. In this study, we aimed to define a generalized disease concept for STXBP1-related disorders and improve prediction. METHODS A cohort of 11 disease-associated and 5 neutral variants (detected in healthy individuals) were tested in 3 cell-free assays and in heterologous cells and primary neurons. Protein aggregation was tested using gel filtration and Triton X-100 insolubility. PRESR (predicting STXBP1-related disorder), a machine learning algorithm that uses both sequence- and 3-dimensional structure-based features, was developed to improve pathogenicity prediction using 231 known disease-associated variants and comparison to our experimental data. RESULTS Disease-associated variants, but none of the neutral variants, produced reduced protein levels. Cell-free assays demonstrated directly that disease-associated variants have reduced thermostability, with most variants denaturing around body temperature. In addition, most disease-associated variants impaired SNARE-mediated membrane fusion in a reconstituted assay. Aggregation/insolubility was observed for none of the variants in vitro or in neurons. PRESR outperformed existing tools substantially: Matthews correlation coefficient = 0.71 versus <0.55. CONCLUSIONS These data establish intrinsic protein instability as the generalizable, primary cause for STXBP1-related disorders and show that protein-specific ortholog and 3-dimensional information improve disease prediction. PRESR is a publicly available diagnostic tool.
Collapse
Affiliation(s)
- Timon André
- Heidelberg University Biochemistry Centre, Heidelberg, Germany
| | - Annemiek A van Berkel
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, the Netherlands; Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNRC), University Medical Center Amsterdam; Amsterdam 1081 HV, the Netherlands
| | - Gurdeep Singh
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Esam T Abualrous
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany; Department of Mathematics and Computer Science, Freie Universität Berlin, Berlin, Germany; Department of Physics, Faculty of Science, Ain Shams University, Cairo, Egypt
| | - Gaurav D Diwan
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Torsten Schmenger
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Lara Braun
- Heidelberg University Biochemistry Centre, Heidelberg, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Centre, Heidelberg, Germany
| | - Ruud F Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, the Netherlands
| | - Christian Freund
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Robert B Russell
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, the Netherlands; Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNRC), University Medical Center Amsterdam; Amsterdam 1081 HV, the Netherlands.
| | | |
Collapse
|
2
|
Akefe IO, Saber SH, Matthews B, Venkatesh BG, Gormal RS, Blackmore DG, Alexander S, Sieriecki E, Gambin Y, Bertran-Gonzalez J, Vitale N, Humeau Y, Gaudin A, Ellis SA, Michaels AA, Xue M, Cravatt B, Joensuu M, Wallis TP, Meunier FA. The DDHD2-STXBP1 interaction mediates long-term memory via generation of saturated free fatty acids. EMBO J 2024; 43:533-567. [PMID: 38316990 PMCID: PMC10897203 DOI: 10.1038/s44318-024-00030-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Revised: 12/06/2023] [Accepted: 12/14/2023] [Indexed: 02/07/2024] Open
Abstract
The phospholipid and free fatty acid (FFA) composition of neuronal membranes plays a crucial role in learning and memory, but the mechanisms through which neuronal activity affects the brain's lipid landscape remain largely unexplored. The levels of saturated FFAs, particularly of myristic acid (C14:0), strongly increase during neuronal stimulation and memory acquisition, suggesting the involvement of phospholipase A1 (PLA1) activity in synaptic plasticity. Here, we show that genetic ablation of the PLA1 isoform DDHD2 in mice dramatically reduces saturated FFA responses to memory acquisition across the brain. Furthermore, DDHD2 loss also decreases memory performance in reward-based learning and spatial memory models prior to the development of neuromuscular deficits that mirror human spastic paraplegia. Via pulldown-mass spectrometry analyses, we find that DDHD2 binds to the key synaptic protein STXBP1. Using STXBP1/2 knockout neurosecretory cells and a haploinsufficient STXBP1+/- mouse model of human early infantile encephalopathy associated with intellectual disability and motor dysfunction, we show that STXBP1 controls targeting of DDHD2 to the plasma membrane and generation of saturated FFAs in the brain. These findings suggest key roles for DDHD2 and STXBP1 in lipid metabolism and in the processes of synaptic plasticity, learning, and memory.
Collapse
Affiliation(s)
- Isaac O Akefe
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
- Academy for Medical Education, Medical School, The University of Queensland, 288 Herston Road, 4006, Brisbane, QLD, Australia
| | - Saber H Saber
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, St Lucia, QLD, 4072, Australia
| | - Benjamin Matthews
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Bharat G Venkatesh
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Rachel S Gormal
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Daniel G Blackmore
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Suzy Alexander
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Emma Sieriecki
- School of Medical Science, University of New South Wales, Randwick, NSW, 2052, Australia
- EMBL Australia, Single Molecule Node, University of New South Wales, Sydney, 2052, Australia
| | - Yann Gambin
- School of Medical Science, University of New South Wales, Randwick, NSW, 2052, Australia
- EMBL Australia, Single Molecule Node, University of New South Wales, Sydney, 2052, Australia
| | | | - Nicolas Vitale
- Institut des Neurosciences Cellulaires et Intégratives, UPR-3212 CNRS - Université de Strasbourg, Strasbourg, France
| | - Yann Humeau
- Interdisciplinary Institute for Neuroscience, CNRS UMR 5297, Université de Bordeaux, Bordeaux, France
| | - Arnaud Gaudin
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Sevannah A Ellis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia
| | - Alysee A Michaels
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
- The Cain Foundation Laboratories, Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital, Houston, TX, USA
| | - Mingshan Xue
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
- The Cain Foundation Laboratories, Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital, Houston, TX, USA
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Benjamin Cravatt
- The Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Merja Joensuu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia.
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, St Lucia, QLD, 4072, Australia.
| | - Tristan P Wallis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia.
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, 4072, Australia.
- The School of Biomedical Sciences, The University of Queensland, St Lucia, QLD, 4072, Australia.
| |
Collapse
|
3
|
Huang M, Wang Y, Chow CH, Stepien KP, Indrawinata K, Xu J, Argiropoulos P, Xie X, Sugita K, Tien CW, Lee S, Monnier PP, Rizo J, Gao S, Sugita S. Double mutation of open syntaxin and UNC-18 P334A leads to excitatory-inhibitory imbalance and impairs multiple aspects of C. elegans behavior. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.18.553709. [PMID: 37645974 PMCID: PMC10462135 DOI: 10.1101/2023.08.18.553709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
SNARE and Sec/Munc18 proteins are essential in synaptic vesicle exocytosis. Open form t-SNARE syntaxin and UNC-18 P334A are well-studied exocytosis-enhancing mutants. Here we investigate the interrelationship between the two mutations by generating double mutants in various genetic backgrounds in C. elegans. While each single mutation rescued the motility of CAPS/unc-31 and synaptotagmin/snt-1 mutants significantly, double mutations unexpectedly worsened motility or lost their rescuing effects. Electrophysiological analyses revealed that simultaneous mutations of open syntaxin and gain-of-function P334A UNC-18 induces a strong imbalance of excitatory over inhibitory transmission. In liposome fusion assays performed with mammalian proteins, the enhancement of fusion caused by the two mutations individually was abolished when the two mutations were introduced simultaneously, consistent with what we observed in C. elegans. We conclude that open syntaxin and P334A UNC-18 do not have additive beneficial effects, and this extends to C. elegans' characteristics such as motility, growth, offspring bared, body size, and exocytosis, as well as liposome fusion in vitro. Our results also reveal unexpected differences between the regulation of exocytosis in excitatory versus inhibitory synapses.
Collapse
Affiliation(s)
- Mengjia Huang
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
| | - Ya Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
| | - Chun Hin Chow
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
| | - Karolina P. Stepien
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, 75390, USA
| | - Karen Indrawinata
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
| | - Junjie Xu
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, 75390, USA
| | - Peter Argiropoulos
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
| | - Xiaoyu Xie
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
- Department of Anesthesiology, Dalian Municipal Friendship Hospital, Dalian Medical University, Dalian, Liaoning, China
| | - Kyoko Sugita
- Donald K. Johnson Eye Institute, University Health Network, Ontario, M5T 0S8, Canada; Department of Ophthalmology & Vision Sciences, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
| | - Chi-Wei Tien
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
| | - Soomin Lee
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
| | - Philippe P. Monnier
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
- Donald K. Johnson Eye Institute, University Health Network, Ontario, M5T 0S8, Canada; Department of Ophthalmology & Vision Sciences, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
| | - Josep Rizo
- Department of Anesthesiology, Dalian Municipal Friendship Hospital, Dalian Medical University, Dalian, Liaoning, China
| | - Shangbang Gao
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
- Key Laboratory of Vascular Aging of the Ministry of Education, Tongji Hospital of Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
| | - Shuzo Sugita
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Ontario, M5T 0S8, Canada
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
| |
Collapse
|
4
|
Kalyana Sundaram RV, Chatterjee A, Bera M, Grushin K, Panda A, Li F, Coleman J, Lee S, Ramakrishnan S, Ernst AM, Gupta K, Rothman JE, Krishnakumar SS. Roles for diacylglycerol in synaptic vesicle priming and release revealed by complete reconstitution of core protein machinery. Proc Natl Acad Sci U S A 2023; 120:e2309516120. [PMID: 37590407 PMCID: PMC10450444 DOI: 10.1073/pnas.2309516120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 07/14/2023] [Indexed: 08/19/2023] Open
Abstract
Here, we introduce the full functional reconstitution of genetically validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, and Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca2+. Using this setup, we identify new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca2+-triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca2+-dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of docked, release-ready vesicles. Dynamic single-molecule imaging of Complexin binding to release-ready vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by chaperones, Munc13 and Munc18. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 "template" complex is a functional intermediate in the production of primed, release-ready vesicles, which requires the coordinated action of Munc13 and Munc18.
Collapse
Affiliation(s)
- R. Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Atrouli Chatterjee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Kirill Grushin
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Aniruddha Panda
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Feng Li
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Seong Lee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Pathology, Yale University School of Medicine, New Haven, CT06520
| | - Andreas M. Ernst
- School of Biological Sciences, University of California San Diego, San Diego, CA92093
| | - Kallol Gupta
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Shyam S. Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Neurology, Yale University School of Medicine, New Haven, CT06520
| |
Collapse
|
5
|
Wang X, Gong J, Zhu L, Chen H, Jin Z, Mo X, Wang S, Yang X, Ma C. Identification of residues critical for the extension of Munc18-1 domain 3a. BMC Biol 2023; 21:158. [PMID: 37443000 PMCID: PMC10347870 DOI: 10.1186/s12915-023-01655-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Accepted: 06/27/2023] [Indexed: 07/15/2023] Open
Abstract
BACKGROUND Neurotransmitter release depends on the fusion of synaptic vesicles with the presynaptic membrane and is mainly mediated by SNARE complex assembly. During the transition of Munc18-1/Syntaxin-1 to the SNARE complex, the opening of the Syntaxin-1 linker region catalyzed by Munc13-1 leads to the extension of the domain 3a hinge loop, which enables domain 3a to bind SNARE motifs in Synaptobrevin-2 and Syntaxin-1 and template the SNARE complex assembly. However, the exact mechanism of domain 3a extension remains elusive. RESULTS Here, we characterized residues on the domain 3a hinge loop that are crucial for the extension of domain 3a by using biophysical and biochemical approaches and electrophysiological recordings. We showed that the mutation of residues T323/M324/R325 disrupted Munc13-1-mediated SNARE complex assembly and membrane fusion starting from Munc18-1/Syntaxin-1 in vitro and caused severe defects in the synaptic exocytosis of mouse cortex neurons in vivo. Moreover, the mutation had no effect on the binding of Synaptobrevin-2 to isolated Munc18-1 or the conformational change of the Syntaxin-1 linker region catalyzed by the Munc13-1 MUN domain. However, the extension of the domain 3a hinge loop in Munc18-1/Syntaxin-1 was completely disrupted by the mutation, leading to the failure of Synaptobrevin-2 binding to Munc18-1/Syntaxin-1. CONCLUSIONS Together with previous results, our data further support the model that the template function of Munc18-1 in SNARE complex assembly requires the extension of domain 3a, and particular residues in the domain 3a hinge loop are crucial for the autoinhibitory release of domain 3a after the MUN domain opens the Syntaxin-1 linker region.
Collapse
Affiliation(s)
- Xianping Wang
- Hubei Key Laboratory of Edible Wild Plants Conservation and Utilization, College of Life Sciences, Hubei Normal University, Huangshi, China
| | - Jihong Gong
- Key Laboratory of Cognitive Science, Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & Treatment, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central Minzu University, Wuhan, China
| | - Le Zhu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Huidan Chen
- Key Laboratory of Cognitive Science, Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & Treatment, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central Minzu University, Wuhan, China
| | - Ziqi Jin
- Key Laboratory of Cognitive Science, Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & Treatment, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central Minzu University, Wuhan, China
| | - Xiaoqiang Mo
- Youjiang Medical University for Nationalities, Baise, China
| | - Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Xiaofei Yang
- Key Laboratory of Cognitive Science, Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & Treatment, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central Minzu University, Wuhan, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| |
Collapse
|
6
|
Wallis TP, Jiang A, Young K, Hou H, Kudo K, McCann AJ, Durisic N, Joensuu M, Oelz D, Nguyen H, Gormal RS, Meunier FA. Super-resolved trajectory-derived nanoclustering analysis using spatiotemporal indexing. Nat Commun 2023; 14:3353. [PMID: 37291117 PMCID: PMC10250379 DOI: 10.1038/s41467-023-38866-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Accepted: 05/11/2023] [Indexed: 06/10/2023] Open
Abstract
Single-molecule localization microscopy techniques are emerging as vital tools to unravel the nanoscale world of living cells by understanding the spatiotemporal organization of protein clusters at the nanometer scale. Current analyses define spatial nanoclusters based on detections but neglect important temporal information such as cluster lifetime and recurrence in "hotspots" on the plasma membrane. Spatial indexing is widely used in video games to detect interactions between moving geometric objects. Here, we use the R-tree spatial indexing algorithm to determine the overlap of the bounding boxes of individual molecular trajectories to establish membership in nanoclusters. Extending the spatial indexing into the time dimension allows the resolution of spatial nanoclusters into multiple spatiotemporal clusters. Using spatiotemporal indexing, we found that syntaxin1a and Munc18-1 molecules transiently cluster in hotspots, offering insights into the dynamics of neuroexocytosis. Nanoscale spatiotemporal indexing clustering (NASTIC) has been implemented as a free and open-source Python graphic user interface.
Collapse
Affiliation(s)
- Tristan P Wallis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia.
| | - Anmin Jiang
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Kyle Young
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Huiyi Hou
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Kye Kudo
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Alex J McCann
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Nela Durisic
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Merja Joensuu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia
- Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Dietmar Oelz
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Hien Nguyen
- School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia
| | - Rachel S Gormal
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia.
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, 4072, Australia.
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, 4072, Australia.
| |
Collapse
|
7
|
Sundaram RVK, Chatterjee A, Bera M, Grushin K, Panda A, Li F, Coleman J, Lee S, Ramakrishnan S, Ernst AM, Gupta K, Rothman JE, Krishnakumar SS. Novel Roles for Diacylglycerol in Synaptic Vesicle Priming and Release Revealed by Complete Reconstitution of Core Protein Machinery. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.05.543781. [PMID: 37333317 PMCID: PMC10274626 DOI: 10.1101/2023.06.05.543781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Here we introduce the full functional reconstitution of genetically-validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca 2+ . Using this novel setup, we discover new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca 2+- triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca 2+ -dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of ready-release vesicles. Dynamic single-molecule imaging of Complexin binding to ready-release vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by Munc13 and Munc18 chaperones. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 'template' complex is a functional intermediate in the production of primed, ready-release vesicles, which requires the coordinated action of Munc13 and Munc18. SIGNIFICANCE STATEMENT Munc13 and Munc18 are SNARE-associated chaperones that act as "priming" factors, facilitating the formation of a pool of docked, release-ready vesicles and regulating Ca 2+ -evoked neurotransmitter release. Although important insights into Munc18/Munc13 function have been gained, how they assemble and operate together remains enigmatic. To address this, we developed a novel biochemically-defined fusion assay which enabled us to investigate the cooperative action of Munc13 and Munc18 in molecular terms. We find that Munc18 nucleates the SNARE complex, while Munc13 promotes and accelerates the SNARE assembly in a DAG-dependent manner. The concerted action of Munc13 and Munc18 stages the SNARE assembly process to ensure efficient 'clamping' and formation of stably docked vesicles, which can be triggered to fuse rapidly (∼10 msec) upon Ca 2+ influx.
Collapse
Affiliation(s)
- R Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Atrouli Chatterjee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Kirill Grushin
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Aniruddha Panda
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Feng Li
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Seong Lee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Andreas M. Ernst
- School of Biological Sciences, University of California San Diego, La Jolla CA 92093, USA
| | - Kallol Gupta
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Shyam S. Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, USA
| |
Collapse
|
8
|
Palfreyman MT, West SE, Jorgensen EM. SNARE Proteins in Synaptic Vesicle Fusion. ADVANCES IN NEUROBIOLOGY 2023; 33:63-118. [PMID: 37615864 DOI: 10.1007/978-3-031-34229-5_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Neurotransmitters are stored in small membrane-bound vesicles at synapses; a subset of synaptic vesicles is docked at release sites. Fusion of docked vesicles with the plasma membrane releases neurotransmitters. Membrane fusion at synapses, as well as all trafficking steps of the secretory pathway, is mediated by SNARE proteins. The SNAREs are the minimal fusion machinery. They zipper from N-termini to membrane-anchored C-termini to form a 4-helix bundle that forces the apposed membranes to fuse. At synapses, the SNAREs comprise a single helix from syntaxin and synaptobrevin; SNAP-25 contributes the other two helices to complete the bundle. Unc13 mediates synaptic vesicle docking and converts syntaxin into the permissive "open" configuration. The SM protein, Unc18, is required to initiate and proofread SNARE assembly. The SNAREs are then held in a half-zippered state by synaptotagmin and complexin. Calcium removes the synaptotagmin and complexin block, and the SNAREs drive vesicle fusion. After fusion, NSF and alpha-SNAP unwind the SNAREs and thereby recharge the system for further rounds of fusion. In this chapter, we will describe the discovery of the SNAREs, their relevant structural features, models for their function, and the central role of Unc18. In addition, we will touch upon the regulation of SNARE complex formation by Unc13, complexin, and synaptotagmin.
Collapse
Affiliation(s)
- Mark T Palfreyman
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Sam E West
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Erik M Jorgensen
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA.
| |
Collapse
|
9
|
Chow CH, Huang M, Sugita S. The Role of Tomosyn in the Regulation of Neurotransmitter Release. ADVANCES IN NEUROBIOLOGY 2023; 33:233-254. [PMID: 37615869 DOI: 10.1007/978-3-031-34229-5_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Soluble NSF attachment protein receptor (SNARE) proteins play a central role in synaptic vesicle (SV) exocytosis. These proteins include the vesicle-associated SNARE protein (v-SNARE) synaptobrevin and the target membrane-associated SNARE proteins (t-SNAREs) syntaxin and SNAP-25. Together, these proteins drive membrane fusion between synaptic vesicles (SV) and the presynaptic plasma membrane to generate SV exocytosis. In the presynaptic active zone, various proteins may either enhance or inhibit SV exocytosis by acting on the SNAREs. Among the inhibitory proteins, tomosyn, a syntaxin-binding protein, is of particular importance because it plays a critical and evolutionarily conserved role in controlling synaptic transmission. In this chapter, we describe how tomosyn was discovered, how it interacts with SNAREs and other presynaptic regulatory proteins to regulate SV exocytosis and synaptic plasticity, and how its various domains contribute to its synaptic functions.
Collapse
Affiliation(s)
- Chun Hin Chow
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Toronto, ON, Canada
- Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Mengjia Huang
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Toronto, ON, Canada
- Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Shuzo Sugita
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Toronto, ON, Canada.
- Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, ON, Canada.
| |
Collapse
|
10
|
Parra-Rivas LA, Palfreyman MT, Vu TN, Jorgensen EM. Interspecies complementation identifies a pathway to assemble SNAREs. iScience 2022; 25:104506. [PMID: 35754735 PMCID: PMC9213704 DOI: 10.1016/j.isci.2022.104506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Revised: 03/23/2022] [Accepted: 05/27/2022] [Indexed: 11/18/2022] Open
Abstract
Unc18 and SNARE proteins form the core of the membrane fusion complex at synapses. To understand the functional interactions within the core machinery, we adopted an "interspecies complementation" approach in Caenorhabditis elegans. Substitutions of individual SNAREs and Unc18 proteins with those from yeast fail to rescue fusion. However, synaptic transmission could be restored in worm-yeast chimeras when two key interfaces were present: an Habc-Unc18 contact site and an Unc18-SNARE motif contact site. A constitutively open form of Unc18 bypasses the requirement for the Habc-Unc18 interface. These data suggest that the Habc domain of syntaxin is required for Unc18 to adopt an open conformation; open Unc18 then templates SNARE complex formation. Finally, we demonstrate that the SNARE and Unc18 machinery in the nematode C. elegans can be replaced by yeast proteins and still carry out synaptic transmission, pointing to the deep evolutionary conservation of these two interfaces.
Collapse
Affiliation(s)
- Leonardo A. Parra-Rivas
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Mark T. Palfreyman
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Thien N. Vu
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Erik M. Jorgensen
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| |
Collapse
|
11
|
Gong J, Wang X, Cui C, Qin Y, Jin Z, Ma C, Yang X. Exploring the Two Coupled Conformational Changes That Activate the Munc18-1/Syntaxin-1 Complex. Front Mol Neurosci 2022; 14:785696. [PMID: 35002621 PMCID: PMC8728020 DOI: 10.3389/fnmol.2021.785696] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 11/26/2021] [Indexed: 11/17/2022] Open
Abstract
Calcium-dependent synaptic vesicle exocytosis is mediated by SNARE complex formation. The transition from the Munc18-1/syntaxin-1 complex to the SNARE complex is catalyzed by the Munc13-1 MUN domain and involves at least two conformational changes: opening of the syntaxin-1 linker region and extension of Munc18-1 domain 3a. However, the relationship and the action order of the two conformational changes remain not fully understood. Here, our data show that an open conformation in the syntaxin-1 linker region can bypass the requirement of the MUN NF sequence. In addition, an extended state of Munc18-1 domain 3a can compensate the role of the syntaxin-1 RI sequence. Altogether, the current data strongly support our previous notion that opening of the syntaxin-1 linker region by Munc13-1 is a key step to initiate SNARE complex assembly, and consequently, Munc18-1 domain 3a can extend its conformation to serve as a template for association of synaptobrevin-2 and syntaxin-1.
Collapse
Affiliation(s)
- Jihong Gong
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Xianping Wang
- Hubei Key Laboratory of Edible Wild Plants Conservation and Utilization, College of Life Sciences, Hubei Normal University, Huangshi, China
| | - Chaoyang Cui
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Yuyang Qin
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Ziqi Jin
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Xiaofei Yang
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| |
Collapse
|
12
|
Munc18-dependent and -independent clustering of syntaxin in the plasma membrane of cultured endocrine cells. Proc Natl Acad Sci U S A 2021; 118:2025748118. [PMID: 34857632 DOI: 10.1073/pnas.2025748118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2021] [Indexed: 11/18/2022] Open
Abstract
Syntaxin helps in catalyzing membrane fusion during exocytosis. It also forms clusters in the plasma membrane, where both its transmembrane and SNARE domains are thought to homo-oligomerize. To study syntaxin clustering in live PC12 cells, we labeled granules with neuropeptide-Y-mCherry and syntaxin clusters with syntaxin-1a green fluorescent protein (GFP). Abundant clusters appeared under total internal reflection (TIRF) illumination, and some of them associated with granules ("on-granule clusters"). Syntaxin-1a-GFP or its mutants were expressed at low levels and competed with an excess of endogenous syntaxin for inclusion into clusters. On-granule inclusion was diminished by mutations known to inhibit binding to Munc18-1 in vitro. Knock-down of Munc18-1 revealed Munc18-dependent and -independent on-granule clustering. Clustering was inhibited by mutations expected to break salt bridges between syntaxin's Hb and SNARE domains and was rescued by additional mutations expected to restore them. Most likely, syntaxin is in a closed conformation when it clusters on granules, and its SNARE and Hb domains approach to within atomic distances. Pairwise replacements of Munc18-contacting residues with alanines had only modest effects, except that the pair R114A/I115A essentially abolished on-granule clustering. In summary, an on-granule cluster arises from the specific interaction between a granule and a dense cluster of syntaxin-Munc18-1 complexes. Off-granule clusters, by contrast, were resistant to even the strongest mutations we tried and required neither Munc18-1 nor the presence of a SNARE domain. They may well form through the nonstoichiometric interactions with membrane lipids that others have observed in cell-free systems.
Collapse
|
13
|
Vardar G, Salazar-Lázaro A, Brockmann M, Weber-Boyvat M, Zobel S, Kumbol VWA, Trimbuch T, Rosenmund C. Reexamination of N-terminal domains of syntaxin-1 in vesicle fusion from central murine synapses. eLife 2021; 10:69498. [PMID: 34427183 PMCID: PMC8416022 DOI: 10.7554/elife.69498] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 08/23/2021] [Indexed: 01/11/2023] Open
Abstract
Syntaxin-1 (STX1) and Munc18-1 are two requisite components of synaptic vesicular release machinery, so much so synaptic transmission cannot proceed in their absence. They form a tight complex through two major binding modes: through STX1’s N-peptide and through STX1’s closed conformation driven by its Habc- domain. However, physiological roles of these two reportedly different binding modes in synapses are still controversial. Here we characterized the roles of STX1’s N-peptide, Habc-domain, and open conformation with and without N-peptide deletion using our STX1-null mouse model system and exogenous reintroduction of STX1A mutants. We show, on the contrary to the general view, that the Habc-domain is absolutely required and N-peptide is dispensable for synaptic transmission. However, STX1A’s N-peptide plays a regulatory role, particularly in the Ca2+-sensitivity and the short-term plasticity of vesicular release, whereas STX1’s open conformation governs the vesicle fusogenicity. Strikingly, we also show neurotransmitter release still proceeds when the two interaction modes between STX1A and Munc18-1 are presumably intervened, necessitating a refinement of the conceptualization of STX1A–Munc18-1 interaction.
Collapse
Affiliation(s)
- Gülçin Vardar
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| | - Andrea Salazar-Lázaro
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| | - Marisa Brockmann
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| | - Marion Weber-Boyvat
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| | - Sina Zobel
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| | | | - Thorsten Trimbuch
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| | - Christian Rosenmund
- Universität Berlin, Humboldt-Universität zu Berlin, Berlin, Germany.,Berlin Institute of Health, Berlin, Germany
| |
Collapse
|
14
|
Tien CW, Yu B, Huang M, Stepien KP, Sugita K, Xie X, Han L, Monnier PP, Zhen M, Rizo J, Gao S, Sugita S. Open syntaxin overcomes exocytosis defects of diverse mutants in C. elegans. Nat Commun 2020; 11:5516. [PMID: 33139696 PMCID: PMC7606450 DOI: 10.1038/s41467-020-19178-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 10/01/2020] [Indexed: 11/09/2022] Open
Abstract
Assembly of SNARE complexes that mediate neurotransmitter release requires opening of a ‘closed’ conformation of UNC-64/syntaxin. Rescue of unc-13/Munc13 mutant phenotypes by overexpressed open UNC-64/syntaxin suggested a specific function of UNC-13/Munc13 in opening UNC-64/ syntaxin. Here, we revisit the effects of open unc-64/syntaxin by generating knockin (KI) worms. The KI animals exhibit enhanced spontaneous and evoked exocytosis compared to WT animals. Unexpectedly, the open syntaxin KI partially suppresses exocytosis defects of various mutants, including snt-1/synaptotagmin, unc-2/P/Q/N-type Ca2+ channel alpha-subunit and unc-31/CAPS, in addition to unc-13/Munc13 and unc-10/RIM, and enhanced exocytosis in tom-1/Tomosyn mutants. However, open syntaxin aggravates the defects of unc-18/Munc18 mutants. Correspondingly, open syntaxin partially bypasses the requirement of Munc13 but not Munc18 for liposome fusion. Our results show that facilitating opening of syntaxin enhances exocytosis in a wide range of genetic backgrounds, and may provide a general means to enhance synaptic transmission in normal and disease states. Opening of the UNC-64/syntaxin closed conformation by UNC-13/Munc13 to form the neuronal SNARE complex is critical for neurotransmitter release. Here the authors show that facilitating the opening of syntaxin enhances exocytosis not only in unc-13 nulls as well as in diverse C. elegans mutants.
Collapse
Affiliation(s)
- Chi-Wei Tien
- Division of Fundamental Neurobiology, Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada, M5T 2S8.,Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - Bin Yu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
| | - Mengjia Huang
- Division of Fundamental Neurobiology, Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada, M5T 2S8.,Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - Karolina P Stepien
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Kyoko Sugita
- Division of Genetics and Development, Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada, M5T 2S8
| | - Xiaoyu Xie
- Division of Fundamental Neurobiology, Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada, M5T 2S8.,Department of Anesthesiology, Dalian Medical University, Dalian, Liaoning, China
| | - Liping Han
- Department of Anesthesiology, Dalian Medical University, Dalian, Liaoning, China.,Department of Anesthesiology, Dalian Municipal Friendship Hospital, Dalian Medical University, Dalian, Liaoning, China
| | - Philippe P Monnier
- Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.,Division of Genetics and Development, Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada, M5T 2S8.,Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - Mei Zhen
- Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.,Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada, M5G 1X5.,Faculty of Medicine, Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada, M5S 1A8
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, USA. .,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, USA. .,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
| | - Shangbang Gao
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China.
| | - Shuzo Sugita
- Division of Fundamental Neurobiology, Krembil Brain Institute, University Health Network, Toronto, Ontario, Canada, M5T 2S8. .,Faculty of Medicine, Department of Physiology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.
| |
Collapse
|
15
|
Wang X, Gong J, Zhu L, Wang S, Yang X, Xu Y, Yang X, Ma C. Munc13 activates the Munc18-1/syntaxin-1 complex and enables Munc18-1 to prime SNARE assembly. EMBO J 2020; 39:e103631. [PMID: 32643828 DOI: 10.15252/embj.2019103631] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Revised: 05/20/2020] [Accepted: 06/02/2020] [Indexed: 11/09/2022] Open
Abstract
Priming of synaptic vesicles involves Munc13-catalyzed transition of the Munc18-1/syntaxin-1 complex to the SNARE complex in the presence of SNAP-25 and synaptobrevin-2; Munc13 drives opening of syntaxin-1 via the MUN domain while Munc18-1 primes SNARE assembly via domain 3a. However, the underlying mechanism remains unclear. In this study, we have identified a number of residues in domain 3a of Munc18-1 that are crucial for Munc13 and Munc18-1 actions in SNARE complex assembly and synaptic vesicle priming. Our results showed that two residues (Q301/K308) at the side of domain 3a mediate the interaction between the Munc18-1/syntaxin-1 complex and the MUN domain. This interaction enables the MUN domain to drive the opening of syntaxin-1 linker region, thereby leading to the extension of domain 3a and promoting synaptobrevin-2 binding. In addition, we identified two residues (K332/K333) at the bottom of domain 3a that mediate the interaction between Munc18-1 and the SNARE motif of syntaxin-1. This interaction ensures Munc18-1 to persistently associate with syntaxin-1 during the conformational change of syntaxin-1 from closed to open, which reinforces the role of Munc18-1 in templating SNARE assembly. Taken together, our data suggest a mechanism by which Munc13 activates the Munc18-1/syntaxin-1 complex and enables Munc18-1 to prime SNARE assembly.
Collapse
Affiliation(s)
- Xianping Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Jihong Gong
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Le Zhu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Xiaoyu Yang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Yuanyuan Xu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Xiaofei Yang
- Key Laboratory of Cognitive Science, Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & Treatment, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China.,Institute of Brain Research, Huazhong University of Science and Technology, Wuhan, China
| |
Collapse
|
16
|
Joshi N, Raveendran A, Nagotu S. Chaperones and Proteostasis: Role in Parkinson's Disease. Diseases 2020; 8:diseases8020024. [PMID: 32580484 PMCID: PMC7349525 DOI: 10.3390/diseases8020024] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/18/2020] [Accepted: 06/19/2020] [Indexed: 02/07/2023] Open
Abstract
Proper folding to attain a defined three-dimensional structure is a prerequisite for the functionality of a protein. Improper folding that eventually leads to formation of protein aggregates is a hallmark of several neurodegenerative disorders. Loss of protein homeostasis triggered by cellular stress conditions is a major contributing factor for the formation of these toxic aggregates. A conserved class of proteins called chaperones and co-chaperones is implicated in maintaining the cellular protein homeostasis. Expanding the body of evidence highlights the role of chaperones as central mediators in the formation, de-aggregation and degradation of the aggregates. Altered expression and function of chaperones is associated with many neurodegenerative diseases including Parkinson’s disease. Several studies indicate that chaperones are at the center of the cause and effect cycle of this disease. An overview of the various chaperones that are associated with homeostasis of Parkinson’s disease-related proteins and their role in pathogenicity will be discussed in this review.
Collapse
|
17
|
Structural and mechanistic insights into secretagogin-mediated exocytosis. Proc Natl Acad Sci U S A 2020; 117:6559-6570. [PMID: 32156735 DOI: 10.1073/pnas.1919698117] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Secretagogin (SCGN) is a hexa-EF-hand protein that is highly expressed in the pancreas, brain, and gastrointestinal tract. SCGN is known to modulate regulated exocytosis in multiple cell lines and tissues; however, its exact functions and underlying mechanisms remain unclear. Here, we report that SCGN interacts with the plasma membrane SNARE SNAP-25, but not the assembled SNARE complex, in a Ca2+-dependent manner. The crystal structure of SCGN in complex with a SNAP-25 fragment reveals that SNAP-25 adopts a helical structure and binds to EF-hands 5 and 6 of SCGN. SCGN strongly inhibits SNARE-mediated vesicle fusion in vitro by binding to SNAP-25. SCGN promotes the plasma membrane localization of SNAP-25, but not Syntaxin-1a, in SCGN-expressing cells. Finally, SCGN controls neuronal growth and brain development in zebrafish, likely via interacting with SNAP-25 or its close homolog, SNAP-23. Our results thus provide insights into the regulation of SNAREs and suggest that aberrant synapse functions underlie multiple neurological disorders caused by SCGN deficiency.
Collapse
|
18
|
Yin P, Gandasi NR, Arora S, Omar-Hmeadi M, Saras J, Barg S. Syntaxin clusters at secretory granules in a munc18-bound conformation. Mol Biol Cell 2018; 29:2700-2708. [PMID: 30156474 PMCID: PMC6249827 DOI: 10.1091/mbc.e17-09-0541] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Syntaxin (stx)-1 is an integral plasma membrane protein that is crucial for two distinct steps of regulated exocytosis, docking of secretory granules at the plasma membrane and membrane fusion. During docking, stx1 clusters at the granule docking site, together with the S/M protein munc18. Here we determined features of stx1 that contribute to its clustering at granules. In live insulin-secreting cells, stx1 and stx3 (but not stx4 or stx11) accumulated at docked granules, and stx1 (but not stx4) rescued docking in cells expressing botulinum neurotoxin-C. Using a series of stx1 deletion mutants and stx1/4 chimeras, we found that all four helical domains (Ha, Hb, Hc, SNARE) and the short N-terminal peptide contribute to recruitment to granules. However, only the Hc domain confers specificity, and it must be derived from stx1 for recruitment to occur. Point mutations in the Hc or the N-terminal peptide designed to interfere with binding to munc18-1 prevent stx1 from clustering at granules, and a mutant munc18 deficient in binding to stx1 does not cluster at granules. We conclude that stx1 is recruited to the docking site in a munc18-1–bound conformation, providing a rationale for the requirement for both proteins for granule docking.
Collapse
Affiliation(s)
- Peng Yin
- Institute of Medical Cell Biology, Uppsala University, 75123 Uppsala, Sweden
| | - Nikhil R Gandasi
- Institute of Medical Cell Biology, Uppsala University, 75123 Uppsala, Sweden
| | - Swati Arora
- Institute of Medical Cell Biology, Uppsala University, 75123 Uppsala, Sweden
| | - Muhmmad Omar-Hmeadi
- Institute of Medical Cell Biology, Uppsala University, 75123 Uppsala, Sweden
| | - Jan Saras
- Institute of Medical Cell Biology, Uppsala University, 75123 Uppsala, Sweden
| | - Sebastian Barg
- Institute of Medical Cell Biology, Uppsala University, 75123 Uppsala, Sweden
| |
Collapse
|
19
|
Rizo J. Mechanism of neurotransmitter release coming into focus. Protein Sci 2018; 27:1364-1391. [PMID: 29893445 DOI: 10.1002/pro.3445] [Citation(s) in RCA: 125] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 05/10/2018] [Indexed: 12/11/2022]
Abstract
Research for three decades and major recent advances have provided crucial insights into how neurotransmitters are released by Ca2+ -triggered synaptic vesicle exocytosis, leading to reconstitution of basic steps that underlie Ca2+ -dependent membrane fusion and yielding a model that assigns defined functions for central components of the release machinery. The soluble N-ethyl maleimide sensitive factor attachment protein receptors (SNAREs) syntaxin-1, SNAP-25, and synaptobrevin-2 form a tight SNARE complex that brings the vesicle and plasma membranes together and is key for membrane fusion. N-ethyl maleimide sensitive factor (NSF) and soluble NSF attachment proteins (SNAPs) disassemble the SNARE complex to recycle the SNAREs for another round of fusion. Munc18-1 and Munc13-1 orchestrate SNARE complex formation in an NSF-SNAP-resistant manner by a mechanism whereby Munc18-1 binds to synaptobrevin and to a self-inhibited "closed" conformation of syntaxin-1, thus forming a template to assemble the SNARE complex, and Munc13-1 facilitates assembly by bridging the vesicle and plasma membranes and catalyzing opening of syntaxin-1. Synaptotagmin-1 functions as the major Ca2+ sensor that triggers release by binding to membrane phospholipids and to the SNAREs, in a tight interplay with complexins that accelerates membrane fusion. Many of these proteins act as both inhibitors and activators of exocytosis, which is critical for the exquisite regulation of neurotransmitter release. It is still unclear how the actions of these various proteins and multiple other components that control release are integrated and, in particular, how they induce membrane fusion, but it can be expected that these fundamental questions can be answered in the near future, building on the extensive knowledge already available.
Collapse
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, 75390
| |
Collapse
|
20
|
Simó A, Just-Borràs L, Cilleros-Mañé V, Hurtado E, Nadal L, Tomàs M, Garcia N, Lanuza MA, Tomàs J. BDNF-TrkB Signaling Coupled to nPKCε and cPKCβI Modulate the Phosphorylation of the Exocytotic Protein Munc18-1 During Synaptic Activity at the Neuromuscular Junction. Front Mol Neurosci 2018; 11:207. [PMID: 29946239 PMCID: PMC6007318 DOI: 10.3389/fnmol.2018.00207] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 05/25/2018] [Indexed: 11/13/2022] Open
Abstract
Munc18-1, a neuron-specific member of the Sec1/Munc18 family, is involved in neurotransmitter release by binding tightly to syntaxin. Munc18-1 is phosphorylated by PKC on Ser-306 and Ser-313 in vitro which reduces the amount of Munc18-1 able to bind syntaxin. We have previously identified that PKC is involved in neurotransmitter release when continuous electrical stimulation imposes a moderate activity on the NMJ and that muscle contraction through TrkB has an important impact on presynaptic PKC isoforms levels, specifically cPKCβI and nPKCε. Therefore, the present study was designed to understand how Munc18-1 phosphorylation is affected by (1) synaptic activity at the neuromuscular junction, (2) nPKCε and cPKCβI isoforms activity, (3) muscle contraction per se, and (4) the BDNF/TrkB signaling in a neuromuscular activity-dependent manner. We performed immunohistochemistry and confocal techniques to evidence the presynaptic location of Munc18-1 in the rat diaphragm muscle. To study synaptic activity, we stimulated the phrenic nerve (1 Hz, 30 min) with or without contraction (abolished by μ-conotoxin GIIIB). Specific inhibitory reagents were used to block nPKCε and cPKCβI activity and to modulate the tropomyosin receptor kinase B (TrkB). Main results obtained from Western blot experiments showed that phosphorylation of Munc18-1 at Ser-313 increases in response to a signaling mechanism initiated by synaptic activity and directly mediated by nPKCε. Otherwise, cPKCβI and TrkB activities work together to prevent this synaptic activity-induced Munc18-1 phosphorylation by a negative regulation of cPKCβI over nPKCε. Therefore, a balance between the activities of these PKC isoforms could be a relevant cue in the regulation of the exocytotic apparatus. The results also demonstrate that muscle contraction prevents the synaptic activity-induced Munc18-1 phosphorylation through a mechanism that opposes the TrkB/cPKCβI/nPKCε signaling.
Collapse
Affiliation(s)
- Anna Simó
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Laia Just-Borràs
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Víctor Cilleros-Mañé
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Erica Hurtado
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Laura Nadal
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Marta Tomàs
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Neus Garcia
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Maria A Lanuza
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| | - Josep Tomàs
- Unitat d'Histologia i Neurobiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain
| |
Collapse
|
21
|
Syntaxins on granules promote docking of granules via interactions with munc18. Sci Rep 2018; 8:193. [PMID: 29317735 PMCID: PMC5760731 DOI: 10.1038/s41598-017-18597-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Accepted: 12/13/2017] [Indexed: 01/02/2023] Open
Abstract
SNAREs and SNARE-binding accessory proteins are believed to be central molecular components of neurotransmitter release, although the precise sequence of molecular events corresponding to distinct physiological states is unclear. The mechanism of docking of vesicles to the plasma membrane remains elusive, as the anchoring protein residing on vesicles is unknown. Here I show that targeting small amounts of syntaxin to granules by transmembrane domain alteration leads to a substantial enhancement of syntaxin clustering beneath granules, as well as of morphological granule docking. The effect was abolished without munc18 and strongly reduced by removal of the N-terminal peptide in the syntaxin mutant. Thus, in contrast to the current paradigm, I demonstrate that syntaxin acts from the vesicular membrane, strongly facilitating docking of vesicles, likely via interaction of its N-peptide with munc18. Docking was assayed by quantifying the syntaxin clusters beneath granules, using two-color Total Internal Reflectance Fluorescence microscopy in live PC-12 cells and confirmed by electron microscopy. Hereby, I propose a new model of vesicle docking, wherein munc18 bridges the few syntaxin molecules residing on granules to the syntaxin cluster on the plasma membrane, suggesting that the number of syntaxins on vesicles determines docking and conceivably fusion probability.
Collapse
|
22
|
Christie MP, Hu SH, Whitten AE, Rehman A, Jarrott RJ, King GJ, Collins BM, Martin JL. Revisiting interaction specificity reveals neuronal and adipocyte Munc18 membrane fusion regulatory proteins differ in their binding interactions with partner SNARE Syntaxins. PLoS One 2017; 12:e0187302. [PMID: 29088285 PMCID: PMC5663490 DOI: 10.1371/journal.pone.0187302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 10/17/2017] [Indexed: 01/01/2023] Open
Abstract
The efficient delivery of cellular cargo relies on the fusion of cargo-carrying vesicles with the correct membrane at the correct time. These spatiotemporal fusion events occur when SNARE proteins on the vesicle interact with cognate SNARE proteins on the target membrane. Regulatory Munc18 proteins are thought to contribute to SNARE interaction specificity through interaction with the SNARE protein Syntaxin. Neuronal Munc18a interacts with Syntaxin1 but not Syntaxin4, and adipocyte Munc18c interacts with Syntaxin4 but not Syntaxin1. Here we show that this accepted view of specificity needs revision. We find that Munc18c interacts with both Syntaxin4 and Syntaxin1, and appears to bind “non-cognate” Syntaxin1 a little more tightly than Syntaxin4. Munc18a binds Syntaxin1 and Syntaxin4, though it interacts with its cognate Syntaxin1 much more tightly. We also observed that when bound to non-cognate Munc18c, Syntaxin1 captures its neuronal SNARE partners SNAP25 and VAMP2, and Munc18c can bind to pre-formed neuronal SNARE ternary complex. These findings reveal that Munc18a and Munc18c bind Syntaxins differently. Munc18c relies principally on the Syntaxin N-peptide interaction for binding Syntaxin4 or Syntaxin1, whereas Munc18a can bind Syntaxin1 tightly whether or not the Syntaxin1 N-peptide is present. We conclude that Munc18a and Munc18c differ in their binding interactions with Syntaxins: Munc18a has two tight binding modes/sites for Syntaxins as defined previously but Munc18c has just one that requires the N-peptide. These results indicate that the interactions between Munc18 and Syntaxin proteins, and the consequences for in vivo function, are more complex than can be accounted for by binding specificity alone.
Collapse
Affiliation(s)
- Michelle P. Christie
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
- * E-mail: (MPC); (JLM)
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Andrew E. Whitten
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Russell J. Jarrott
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Gordon J. King
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Brett M. Collins
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
- Griffith Institute for Drug Discovery, Griffith University, Nathan, Queensland, Australia
- * E-mail: (MPC); (JLM)
| |
Collapse
|
23
|
Rehman A, Hu SH, Tnimov Z, Whitten AE, King GJ, Jarrott RJ, Norwood SJ, Alexandrov K, Collins BM, Christie MP, Martin JL. The nature of the Syntaxin4 C-terminus affects Munc18c-supported SNARE assembly. PLoS One 2017; 12:e0183366. [PMID: 28841669 PMCID: PMC5571939 DOI: 10.1371/journal.pone.0183366] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 08/02/2017] [Indexed: 11/18/2022] Open
Abstract
Vesicular transport of cellular cargo requires targeted membrane fusion and formation of a SNARE protein complex that draws the two apposing fusing membranes together. Insulin-regulated delivery and fusion of glucose transporter-4 storage vesicles at the cell surface is dependent on two key proteins: the SNARE integral membrane protein Syntaxin4 (Sx4) and the soluble regulatory protein Munc18c. Many reported in vitro studies of Munc18c:Sx4 interactions and of SNARE complex formation have used soluble Sx4 constructs lacking the native transmembrane domain. As a consequence, the importance of the Sx4 C-terminal anchor remains poorly understood. Here we show that soluble C-terminally truncated Sx4 dissociates more rapidly from Munc18c than Sx4 where the C-terminal transmembrane domain is replaced with a T4-lysozyme fusion. We also show that Munc18c appears to inhibit SNARE complex formation when soluble C-terminally truncated Sx4 is used but does not inhibit SNARE complex formation when Sx4 is C-terminally anchored (by a C-terminal His-tag bound to resin, by a C-terminal T4L fusion or by the native C-terminal transmembrane domain in detergent micelles). We conclude that the C-terminus of Sx4 is critical for its interaction with Munc18c, and that the reported inhibitory role of Munc18c may be an artifact of experimental design. These results support the notion that a primary role of Munc18c is to support SNARE complex formation and membrane fusion.
Collapse
Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Zakir Tnimov
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Andrew E. Whitten
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Gordon J. King
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Russell J. Jarrott
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Suzanne J. Norwood
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Kirill Alexandrov
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Brett M. Collins
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Michelle P. Christie
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
- * E-mail: (MPC); (JLM)
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
- * E-mail: (MPC); (JLM)
| |
Collapse
|
24
|
UNC-18 and Tomosyn Antagonistically Control Synaptic Vesicle Priming Downstream of UNC-13 in Caenorhabditis elegans. J Neurosci 2017; 37:8797-8815. [PMID: 28821673 DOI: 10.1523/jneurosci.0338-17.2017] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Revised: 07/21/2017] [Accepted: 08/03/2017] [Indexed: 11/21/2022] Open
Abstract
Munc18-1/UNC-18 is believed to prime SNARE-mediated membrane fusion, yet the underlying mechanisms remain enigmatic. Here, we examine how potential gain-of-function mutations of Munc18-1/UNC-18 affect locomotory behavior and synaptic transmission, and how Munc18-1-mediated priming is related to Munc13-1/UNC-13 and Tomosyn/TOM-1, positive and negative SNARE regulators, respectively. We show that a Munc18-1(P335A)/UNC-18(P334A) mutation leads to significantly increased locomotory activity and acetylcholine release in Caenorhabditis elegans, as well as enhanced synaptic neurotransmission in cultured mammalian neurons. Importantly, similar to tom-1 null mutants, unc-18(P334A) mutants partially bypass the requirement of UNC-13. Moreover, unc-18(P334A) and tom-1 null mutations confer a strong synergy in suppressing the phenotypes of unc-13 mutants. Through biochemical experiments, we demonstrate that Munc18-1(P335A) exhibits enhanced activity in SNARE complex formation as well as in binding to the preformed SNARE complex, and partially bypasses the Munc13-1 requirement in liposome fusion assays. Our results indicate that Munc18-1/UNC-18 primes vesicle fusion downstream of Munc13-1/UNC-13 by templating SNARE complex assembly and acts antagonistically with Tomosyn/TOM-1.SIGNIFICANCE STATEMENT At presynaptic sites, SNARE-mediated membrane fusion is tightly regulated by several key proteins including Munc18/UNC-18, Munc13/UNC-13, and Tomosyn/TOM-1. However, how these proteins interact with each other to achieve the precise regulation of neurotransmitter release remains largely unclear. Using Caenorhabditis elegans as an in vivo model, we found that a gain-of-function mutant of UNC-18 increases locomotory activity and synaptic acetylcholine release, that it partially bypasses the requirement of UNC-13 for release, and that this bypass is synergistically augmented by the lack of TOM-1. We also elucidated the biochemical basis for the gain-of-function caused by this mutation. Thus, our study provides novel mechanistic insights into how Munc18/UNC-18 primes synaptic vesicle release and how this protein interacts functionally with Munc13/UNC-13 and Tomosyn/TOM-1.
Collapse
|
25
|
Suri M, Evers JMG, Laskowski RA, O'Brien S, Baker K, Clayton-Smith J, Dabir T, Josifova D, Joss S, Kerr B, Kraus A, McEntagart M, Morton J, Smith A, Splitt M, Thornton JM, Wright CF. Protein structure and phenotypic analysis of pathogenic and population missense variants in STXBP1. Mol Genet Genomic Med 2017; 5:495-507. [PMID: 28944233 PMCID: PMC5606886 DOI: 10.1002/mgg3.304] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 05/17/2017] [Accepted: 05/20/2017] [Indexed: 01/07/2023] Open
Abstract
Background Syntaxin‐binding protein 1, encoded by STXBP1, is highly expressed in the brain and involved in fusing synaptic vesicles with the plasma membrane. Studies have shown that pathogenic loss‐of‐function variants in this gene result in various types of epilepsies, mostly beginning early in life. We were interested to model pathogenic missense variants on the protein structure to investigate the mechanism of pathogenicity and genotype–phenotype correlations. Methods We report 11 patients with pathogenic de novo mutations in STXBP1 identified in the first 4293 trios of the Deciphering Developmental Disorder (DDD) study, including six missense variants. We analyzed the structural locations of the pathogenic missense variants from this study and the literature, as well as population missense variants extracted from Exome Aggregation Consortium (ExAC). Results Pathogenic variants are significantly more likely to occur at highly conserved locations than population variants, and be buried inside the protein domain. Pathogenic mutations are also more likely to destabilize the domain structure compared with population variants, increasing the proportion of (partially) unfolded domains that are prone to aggregation or degradation. We were unable to detect any genotype–phenotype correlation, but unlike previously reported cases, most of the DDD patients with STXBP1 pathogenic variants did not present with very early‐onset or severe epilepsy and encephalopathy, though all have developmental delay with intellectual disability and most display behavioral problems and suffered seizures in later childhood. Conclusion Variants across STXBP1 that cause loss of function can result in severe intellectual disability with or without seizures, consistent with a haploinsufficiency mechanism. Pathogenic missense mutations act through destabilization of the protein domain, making it prone to aggregation or degradation. The presence or absence of early seizures may reflect ascertainment bias in the literature as well as the broad recruitment strategy of the DDD study.
Collapse
Affiliation(s)
- Mohnish Suri
- Nottingham Regional Genetics ServiceNottingham University Hospitals NHS TrustCity Hospital Campus, The Gables, Hucknall RoadNottinghamNG5 1PBUK
| | - Jochem M G Evers
- European Bioinformatics Institute (EMBL-EBI)Wellcome Genome Campus, HinxtonCambridgeCB10 1SDUK
| | - Roman A Laskowski
- European Bioinformatics Institute (EMBL-EBI)Wellcome Genome Campus, HinxtonCambridgeCB10 1SDUK
| | - Sinead O'Brien
- MRC Cognition and Brain Sciences Unit15 Chaucer RoadCambridgeCB2 7EFUK
| | - Kate Baker
- MRC Cognition and Brain Sciences Unit15 Chaucer RoadCambridgeCB2 7EFUK.,Department of Medical GeneticsUniversity of CambridgeCambridge Biomedical CampusCambridgeCB2 0QQUK
| | - Jill Clayton-Smith
- Manchester Centre for Genomic MedicineSt Mary's Hospital, Central Manchester University Hospitals NHS Foundation TrustManchester Academic Health Science CentreManchesterM13 9WLUK
| | - Tabib Dabir
- Northern Ireland Regional Genetics CentreBelfast Health and Social Care TrustBelfast City HospitalLisburn RoadBelfastBT9 7ABUK
| | - Dragana Josifova
- South East Thames Regional Genetics CentreGuy's and St Thomas' NHS Foundation TrustGuy's HospitalGreat Maze PondLondonSE1 9RTUK
| | - Shelagh Joss
- West of Scotland Genetics ServiceQueen Elizabeth University HospitalLaboratory Medicine BuildingGlasgowG51 4TFUK
| | - Bronwyn Kerr
- Manchester Centre for Genomic MedicineSt Mary's Hospital, Central Manchester University Hospitals NHS Foundation TrustManchester Academic Health Science CentreManchesterM13 9WLUK
| | - Alison Kraus
- Yorkshire Regional Genetics ServiceDepartment of Clinical GeneticsLeeds Teaching Hospitals NHS TrustChapel Allerton HospitalChapeltown RoadLeedsLS7 4SAUK
| | - Meriel McEntagart
- South West Thames Regional Genetics CentreSt George's Healthcare NHS TrustSt George's University of LondonCranmer TerraceLondonSW17 0REUK
| | - Jenny Morton
- West Midlands Regional Clinical Genetics Service and Birmingham Health PartnersBirmingham Women's and Children's NHS Foundation TrustBirmingham Women's HospitalMindelsohn Way, EdgbastonBirminghamB15 2TGUK
| | - Audrey Smith
- Yorkshire Regional Genetics ServiceDepartment of Clinical GeneticsLeeds Teaching Hospitals NHS TrustChapel Allerton HospitalChapeltown RoadLeedsLS7 4SAUK
| | - Miranda Splitt
- Northern Genetics ServiceNewcastle upon Tyne Hospitals NHS Foundation TrustInstitute of Human GeneticsInternational Centre for LifeCentral ParkwayNewcastle upon TyneNE1 3BZUK
| | - Janet M Thornton
- European Bioinformatics Institute (EMBL-EBI)Wellcome Genome Campus, HinxtonCambridgeCB10 1SDUK
| | | | - Caroline F Wright
- Wellcome Trust Sanger InstituteWellcome Genome Campus, HinxtonCambridgeCB1 8RQUK.,University of Exeter Medical SchoolRoyal Devon & Exeter HospitalBarrack RoadExeterEX2 5DWUK
| |
Collapse
|
26
|
Qin T, Liang T, Zhu D, Kang Y, Xie L, Dolai S, Sugita S, Takahashi N, Ostenson CG, Banks K, Gaisano HY. Munc18b Increases Insulin Granule Fusion, Restoring Deficient Insulin Secretion in Type-2 Diabetes Human and Goto-Kakizaki Rat Islets with Improvement in Glucose Homeostasis. EBioMedicine 2017; 16:262-274. [PMID: 28163042 PMCID: PMC5474508 DOI: 10.1016/j.ebiom.2017.01.030] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 01/09/2017] [Accepted: 01/20/2017] [Indexed: 01/22/2023] Open
Abstract
Reduced pancreatic islet levels of Munc18a/SNARE complex proteins have been postulated to contribute to the deficient glucose-stimulated insulin secretion (GSIS) in type-2 diabetes (T2D). Whereas much previous work has purported Munc18a/SNARE complex (Syntaxin-1A/VAMP-2/SNAP25) to be primarily involved in predocked secretory granule (SG) fusion, less is known about newcomer SGs that undergo minimal docking time at the plasma membrane before fusion. Newcomer SG fusion has been postulated to involve a distinct SM/SNARE complex (Munc18b/Syntaxin-3/VAMP8/SNAP25), whose levels we find also reduced in islets of T2D humans and T2D Goto-Kakizaki (GK) rats. Munc18b overexpression by adenovirus infection (Ad-Munc18b), by increasing assembly of Munc18b/SNARE complexes, mediated increased fusion of not only newcomer SGs but also predocked SGs in T2D human and GK rat islets, resulting in rescue of the deficient biphasic GSIS. Infusion of Ad-Munc18b into GK rat pancreas led to sustained improvement in glucose homeostasis. However, Munc18b overexpression in normal islets increased only newcomer SG fusion. Therefore, Munc18b could potentially be deployed in human T2D to rescue the deficient GSIS. Human T2D islet β-cells exhibit reduced fusion of predocked & newcomer secretory granules (SGs). Munc18b increases SNARE complexes involved in fusions of both newcomer & predocked SGs. Munc18b rescue of newcomer & predocked SGs increased biphasic secretion in human T2D β-cells. Munc18b rescue of T2D Goto-Kakizaki rat β-cell secretion improves glucose homeostasis.
Deficient insulin secretion from pancreatic islet β-cells in type-2 diabetes (T2D) is partly due to reduced expression of many proteins that assemble into specific complexes that mediate fusion of insulin secretory granules (SGs) with plasma membrane, termed exocytosis. We here show we can infuse a virus that contains the construct of one of the SG fusion proteins, Munc18b, into pancreatic ducts of T2D rats to reach the islets, which restored insulin secretion and improved glycemic control. Munc18b acts to promote the assembly of SG fusion complexes. This strategy could potentially be applied to treat human T2D by endoscopic infusion.
Collapse
Affiliation(s)
- Tairan Qin
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Dan Zhu
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Youhou Kang
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Li Xie
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Subhankar Dolai
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Shuzo Sugita
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada; Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Noriko Takahashi
- Laboratory of Physiological Chemistry, Institute of Medicinal Chemistry, Hoshi University, Shinagawa, Tokyo 142-8501, Japan
| | - Claes-Goran Ostenson
- Department of Molecular Medicine and Surgery, Endocrinology and Diabetology Unit, Karolinska Institutet, Karolinska University Hospital, SE-171 76 Stockholm, Sweden
| | - Kate Banks
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada; Division of Comparative Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Herbert Y Gaisano
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada.
| |
Collapse
|
27
|
Dun AR, Lord GJ, Wilson RS, Kavanagh DM, Cialowicz KI, Sugita S, Park S, Yang L, Smyth AM, Papadopulos A, Rickman C, Duncan RR. Navigation through the Plasma Membrane Molecular Landscape Shapes Random Organelle Movement. Curr Biol 2017; 27:408-414. [PMID: 28089515 PMCID: PMC5300901 DOI: 10.1016/j.cub.2016.12.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 09/05/2016] [Accepted: 12/02/2016] [Indexed: 12/13/2022]
Abstract
Eukaryotic plasma membrane organization theory has long been controversial, in part due to a dearth of suitably high-resolution techniques to probe molecular architecture in situ and integrate information from diverse data streams [1]. Notably, clustered patterning of membrane proteins is a commonly conserved feature across diverse protein families (reviewed in [2]), including the SNAREs [3], SM proteins [4, 5], ion channels [6, 7], and receptors (e.g., [8]). Much effort has gone into analyzing the behavior of secretory organelles [9-13], and understanding the relationship between the membrane and proximal organelles [4, 5, 12, 14] is an essential goal for cell biology as broad concepts or rules may be established. Here we explore the generally accepted model that vesicles at the plasmalemma are guided by cytoskeletal tracks to specific sites on the membrane that have clustered molecular machinery for secretion [15], organized in part by the local lipid composition [16]. To increase our understanding of these fundamental processes, we integrated nanoscopy and spectroscopy of the secretory machinery with organelle tracking data in a mathematical model, iterating with knockdown cell models. We find that repeated routes followed by successive vesicles, the re-use of similar fusion sites, and the apparently distinct vesicle "pools" are all fashioned by the Brownian behavior of organelles overlaid on navigation between non-reactive secretory protein molecular depots patterned at the plasma membrane.
Collapse
Affiliation(s)
- Alison R Dun
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Gabriel J Lord
- Department of Mathematics, Maxwell Institute, MACS, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Rhodri S Wilson
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Deirdre M Kavanagh
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Katarzyna I Cialowicz
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Shuzo Sugita
- Toronto Western Research Institute, Room 11-432, McLaughlin Wing, 399 Bathurst St., Toronto, ON M5T 2S8, Canada
| | - Seungmee Park
- Toronto Western Research Institute, Room 11-432, McLaughlin Wing, 399 Bathurst St., Toronto, ON M5T 2S8, Canada
| | - Lei Yang
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Annya M Smyth
- Centre for Inflammation Research, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
| | - Andreas Papadopulos
- The Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Rory R Duncan
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium.
| |
Collapse
|
28
|
Kasula R, Chai YJ, Bademosi AT, Harper CB, Gormal RS, Morrow IC, Hosy E, Collins BM, Choquet D, Papadopulos A, Meunier FA. The Munc18-1 domain 3a hinge-loop controls syntaxin-1A nanodomain assembly and engagement with the SNARE complex during secretory vesicle priming. J Cell Biol 2016; 214:847-58. [PMID: 27646276 PMCID: PMC5037406 DOI: 10.1083/jcb.201508118] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2015] [Accepted: 08/24/2016] [Indexed: 12/12/2022] Open
Abstract
Kasula et al. use single-molecule imaging to reveal the diffusional signature for the SNARE proteins Munc18-1 and syntaxin-1A during secretory vesicle priming. The authors show that a conformational change in the Munc18-1 domain 3a hinge-loop regulates engagement of syntaxin-1A in the SNARE complex. Munc18-1 and syntaxin-1A control SNARE-dependent neuroexocytosis and are organized in nanodomains on the plasma membrane of neurons and neurosecretory cells. Deciphering the intra- and intermolecular steps via which they prepare secretory vesicles (SVs) for fusion is key to understanding neuronal and hormonal communication. Here, we demonstrate that expression of a priming-deficient mutant lacking 17 residues of the domain 3a hinge-loop (Munc18-1Δ317-333) in PC12 cells engineered to knockdown Munc18-1/2 markedly prolonged SV docking. Single-molecule analysis revealed nonhomogeneous diffusion of Munc18-1 and syntaxin-1A in and out of partially overlapping nanodomains. Whereas Munc18-1WT mobility increased in response to stimulation, syntaxin-1A became less mobile. These Munc18-1 and syntaxin-1A diffusional switches were blocked by the expression of Munc18-1Δ317-333, suggesting that a conformational change in the Munc18-1 hinge-loop controls syntaxin-1A and subsequent SNARE complex assembly. Accordingly, syntaxin-1A confinement was prevented by expression of botulinum neurotoxin type E. The Munc18-1 domain 3a hinge-loop therefore controls syntaxin-1A engagement into SNARE complex formation during priming.
Collapse
Affiliation(s)
- Ravikiran Kasula
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Ye Jin Chai
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Adekunle T Bademosi
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Callista B Harper
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Rachel S Gormal
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Isabel C Morrow
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Eric Hosy
- Interdisciplinary Institute for Neuroscience, University of Bordeaux, 33077 Bordeaux, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5297, 33077 Bordeaux, France
| | - Brett M Collins
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Daniel Choquet
- Interdisciplinary Institute for Neuroscience, University of Bordeaux, 33077 Bordeaux, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5297, 33077 Bordeaux, France Bordeaux Imaging Center, Unité Mixte de Service 3420, Centre National de la Recherche Scientifique, US4 Institut National de la Santé et de la Recherche Médicale, University of Bordeaux, 33077 Bordeaux, France
| | - Andreas Papadopulos
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Frédéric A Meunier
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland 4072, Australia
| |
Collapse
|
29
|
Chai YJ, Sierecki E, Tomatis VM, Gormal RS, Giles N, Morrow IC, Xia D, Götz J, Parton RG, Collins BM, Gambin Y, Meunier FA. Munc18-1 is a molecular chaperone for α-synuclein, controlling its self-replicating aggregation. J Cell Biol 2016; 214:705-18. [PMID: 27597756 PMCID: PMC5021092 DOI: 10.1083/jcb.201512016] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 08/03/2016] [Indexed: 01/06/2023] Open
Abstract
Munc18-1 heterozygous mutations are associated with developmental diseases, including early infantile epileptic encephalopathy (EIEE). Chai et al. report that Munc18-1 acts as a chaperone for α-synuclein and controls its aggregative propensity. Munc18-1 EIEE-associated mutations promote the aggregation of endogenous α-synuclein in neurons, leading to a neurodegenerative phenotype. Munc18-1 is a key component of the exocytic machinery that controls neurotransmitter release. Munc18-1 heterozygous mutations cause developmental defects and epileptic phenotypes, including infantile epileptic encephalopathy (EIEE), suggestive of a gain of pathological function. Here, we used single-molecule analysis, gene-edited cells, and neurons to demonstrate that Munc18-1 EIEE-causing mutants form large polymers that coaggregate wild-type Munc18-1 in vitro and in cells. Surprisingly, Munc18-1 EIEE mutants also form Lewy body–like structures that contain α-synuclein (α-Syn). We reveal that Munc18-1 binds α-Syn, and its EIEE mutants coaggregate α-Syn. Likewise, removal of endogenous Munc18-1 increases the aggregative propensity of α-SynWT and that of the Parkinson’s disease–causing α-SynA30P mutant, an effect rescued by Munc18-1WT expression, indicative of chaperone activity. Coexpression of the α-SynA30P mutant with Munc18-1 reduced the number of α-SynA30P aggregates. Munc18-1 mutations and haploinsufficiency may therefore trigger a pathogenic gain of function through both the corruption of native Munc18-1 and a perturbed chaperone activity for α-Syn leading to aggregation-induced neurodegeneration.
Collapse
Affiliation(s)
- Ye Jin Chai
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Emma Sierecki
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia Single Molecule Sciences Centre, European Molecular Biology Laboratory Australia, The University of New South Wales, Sydney 2052, Australia
| | - Vanesa M Tomatis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Rachel S Gormal
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Nichole Giles
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia Single Molecule Sciences Centre, European Molecular Biology Laboratory Australia, The University of New South Wales, Sydney 2052, Australia
| | - Isabel C Morrow
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Di Xia
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Jürgen Götz
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Robert G Parton
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Brett M Collins
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Yann Gambin
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia Single Molecule Sciences Centre, European Molecular Biology Laboratory Australia, The University of New South Wales, Sydney 2052, Australia
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| |
Collapse
|
30
|
Propofol-induced Inhibition of Catecholamine Release Is Reversed by Maintaining Calcium Influx. Anesthesiology 2016; 124:878-84. [PMID: 26808630 DOI: 10.1097/aln.0000000000001015] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
BACKGROUND Propofol (2,6-diisopropylphenol) is one of the most frequently used anesthetic agents. One of the main side effects of propofol is to reduce blood pressure, which is thought to occur by inhibiting the release of catecholamines from sympathetic neurons. Here, the authors hypothesized that propofol-induced hypotension is not simply the result of suppression of the release mechanisms for catecholamines. METHODS The authors simultaneously compared the effects of propofol on the release of norepinephrine triggered by high K-induced depolarization, as well as ionomycin, by using neuroendocrine PC12 cells and synaptosomes. Ionomycin, a Ca ionophore, directly induces Ca influx, thus bypassing the effect of ion channel modulation by propofol. RESULTS Propofol decreased depolarization (high K)-triggered norepinephrine release, whereas it increased ionomycin-triggered release from both PC12 cells and synaptosomes. The propofol (30 μM)-induced increase in norepinephrine release triggered by ionomycin was dependent on both the presence and the concentration of extracellular Ca (0.3 to 10 mM; n = 6). The enhancement of norepinephrine release by propofol was observed in all tested concentrations of ionomycin (0.1 to 5 μM; n = 6). CONCLUSIONS Propofol at clinically relevant concentrations promotes the catecholamine release as long as Ca influx is supported. This unexpected finding will allow for a better understanding in preventing propofol-induced hypotension.
Collapse
|
31
|
Abstract
Extensive research has yielded crucial insights into the mechanism of neurotransmitter release, and working models for the functions of key proteins involved in release. The SNAREs Syntaxin-1, Synaptobrevin, and SNAP-25 play a central role in membrane fusion, forming SNARE complexes that bridge the vesicle and plasma membranes and that are disassembled by NSF-SNAPs. Exocytosis likely starts with Syntaxin-1 folded into a self-inhibited closed conformation that binds to Munc18-1. Munc13s open Syntaxin-1, orchestrating SNARE complex assembly in an NSF-SNAP-resistant manner together with Munc18-1. In the resulting primed state, with partially assembled SNARE complexes, fusion is inhibited by Synaptotagmin-1 and Complexins, which also perform active functions in release. Upon influx of Ca(2+), Synaptotagmin-1 activates fast release, likely by relieving the inhibition caused by Complexins and cooperating with the SNAREs in bringing the membranes together. Although alternative models exist and fundamental questions remain unanswered, a definitive description of the basic release mechanism may be available soon.
Collapse
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry, and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390;
| | | |
Collapse
|
32
|
Park S, Bin NR, Rajah M, Kim B, Chou TC, Kang SYA, Sugita K, Parsaud L, Smith M, Monnier PP, Ikura M, Zhen M, Sugita S. Conformational states of syntaxin-1 govern the necessity of N-peptide binding in exocytosis of PC12 cells and Caenorhabditis elegans. Mol Biol Cell 2015; 27:669-85. [PMID: 26700321 PMCID: PMC4750926 DOI: 10.1091/mbc.e15-09-0638] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 12/18/2015] [Indexed: 11/11/2022] Open
Abstract
Syntaxin-1 is the central SNARE protein for neuronal exocytosis. It interacts with Munc18-1 through its cytoplasmic domains, including the N-terminal peptide (N-peptide). Here we examine the role of the N-peptide binding in two conformational states ("closed" vs. "open") of syntaxin-1 using PC12 cells and Caenorhabditis elegans. We show that expression of "closed" syntaxin-1A carrying N-terminal single point mutations (D3R, L8A) that perturb interaction with the hydrophobic pocket of Munc18-1 rescues impaired secretion in syntaxin-1-depleted PC12 cells and the lethality and lethargy of unc-64 (C. elegans orthologue of syntaxin-1)-null mutants. Conversely, expression of the "open" syntaxin-1A harboring the same mutations fails to rescue the impairments. Biochemically, the L8A mutation alone slightly weakens the binding between "closed" syntaxin-1A and Munc18-1, whereas the same mutation in the "open" syntaxin-1A disrupts it. Our results reveal a striking interplay between the syntaxin-1 N-peptide and the conformational state of the protein. We propose that the N-peptide plays a critical role in intracellular trafficking of syntaxin-1, which is dependent on the conformational state of this protein. Surprisingly, however, the N-peptide binding mode seems dispensable for SNARE-mediated exocytosis per se, as long as the protein is trafficked to the plasma membrane.
Collapse
Affiliation(s)
- Seungmee Park
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Na-Ryum Bin
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Maaran Rajah
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Byungjin Kim
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Ting-Chieh Chou
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Soo-Young Ann Kang
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Kyoko Sugita
- Division of Genetics and Development, Krembil Discovery Tower, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Leon Parsaud
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Matthew Smith
- Division of Signaling Biology, MaRS Toronto Medical Discovery Tower, Ontario Cancer Institute, University Health Network, Toronto, ON M5G 1L7, Canada Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 1L7, Canada
| | - Philippe P Monnier
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Division of Genetics and Development, Krembil Discovery Tower, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Mitsuhiko Ikura
- Division of Genetics and Development, Krembil Discovery Tower, University Health Network, Toronto, ON M5T 2S8, Canada Division of Signaling Biology, MaRS Toronto Medical Discovery Tower, Ontario Cancer Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Mei Zhen
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Shuzo Sugita
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| |
Collapse
|
33
|
Bin NR, Jung CH, Kim B, Chandrasegram P, Turlova E, Zhu D, Gaisano HY, Sun HS, Sugita S. Chaperoning of closed syntaxin-3 through Lys46 and Glu59 in domain 1 of Munc18 proteins is indispensable for mast cell exocytosis. J Cell Sci 2015; 128:1946-60. [PMID: 25795302 DOI: 10.1242/jcs.165662] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 03/16/2015] [Indexed: 11/20/2022] Open
Abstract
Understanding how Munc18 proteins govern exocytosis is crucial because mutations of this protein cause severe secretion deficits in neuronal and immune cells. Munc18-2 has indispensable roles in the degranulation of mast cell, partly by binding and chaperoning a subset of syntaxin isoforms. However, the key syntaxin that, crucially, participates in the degranulation – whose levels and intracellular localization are regulated by Munc18-2 – remains unknown. Here, we demonstrate that double knockdown of Munc18-1 and Munc-2 in mast cells results in greatly reduced degranulation accompanied with strikingly compromised expression levels and localization of syntaxin-3. This phenotype is fully rescued by wild-type Munc18 proteins but not by the K46E, E59K and K46E/E59K mutants of Munc-18 domain 1, each of which exhibits completely abolished binding to 'closed' syntaxin-3. Furthermore, knockdown of syntaxin-3 strongly impairs degranulation. Collectively, our data argue that residues Lys46 and Glu59 of Munc18 proteins are indispensable for mediating the interaction between Munc18 and closed syntaxin-3, which is essential for degranulation by chaperoning syntaxin-3. Our results also indicate that the functional contribution of these residues differs between immune cell degranulation and neuronal secretion.
Collapse
Affiliation(s)
- Na-Ryum Bin
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Chang Hun Jung
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Byungjin Kim
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada
| | - Prashanth Chandrasegram
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada
| | - Ekaterina Turlova
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Dan Zhu
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Herbert Y Gaisano
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Hong-Shuo Sun
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Shuzo Sugita
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| |
Collapse
|
34
|
Hemophagocytic lymphohistiocytosis caused by dominant-negative mutations in STXBP2 that inhibit SNARE-mediated membrane fusion. Blood 2015; 125:1566-77. [PMID: 25564401 DOI: 10.1182/blood-2014-11-610816] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Familial hemophagocytic lymphohistiocytosis (F-HLH) and Griscelli syndrome type 2 (GS) are life-threatening immunodeficiencies characterized by impaired cytotoxic T lymphocyte (CTL) and natural killer (NK) cell lytic activity. In the majority of cases, these disorders are caused by biallelic inactivating germline mutations in genes such as RAB27A (GS) and PRF1, UNC13D, STX11, and STXBP2 (F-HLH). Although monoallelic (ie, heterozygous) mutations have been identified in certain patients, the clinical significance and molecular mechanisms by which these mutations influence CTL and NK cell function remain poorly understood. Here, we characterize 2 novel monoallelic hemophagocytic lymphohistiocytosis (HLH)-associated mutations affecting codon 65 of STXPB2, the gene encoding Munc18-2, a member of the SEC/MUNC18 family. Unlike previously described Munc18-2 mutants, Munc18-2(R65Q) and Munc18-2(R65W) retain the ability to interact with and stabilize syntaxin 11. However, presence of Munc18-2(R65Q/W) in patient-derived lymphocytes and forced expression in control CTLs and NK cells diminishes degranulation and cytotoxic activity. Mechanistic studies reveal that mutations affecting R65 hinder membrane fusion in vitro by arresting the late steps of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-complex assembly. Collectively, these results reveal a direct role for SEC/MUNC18 proteins in promoting SNARE-complex assembly in vivo and suggest that STXBP2 R65 mutations operate in a novel dominant-negative fashion to impair lytic granule fusion and contribute to HLH.
Collapse
|
35
|
Rehman A, Archbold JK, Hu SH, Norwood SJ, Collins BM, Martin JL. Reconciling the regulatory role of Munc18 proteins in SNARE-complex assembly. IUCRJ 2014; 1:505-513. [PMID: 25485130 PMCID: PMC4224468 DOI: 10.1107/s2052252514020727] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/15/2014] [Indexed: 06/04/2023]
Abstract
Membrane fusion is essential for human health, playing a vital role in processes as diverse as neurotransmission and blood glucose control. Two protein families are key: (1) the Sec1p/Munc18 (SM) and (2) the soluble N-ethylmaleimide-sensitive attachment protein receptor (SNARE) proteins. Whilst the essential nature of these proteins is irrefutable, their exact regulatory roles in membrane fusion remain controversial. In particular, whether SM proteins promote and/or inhibit the SNARE-complex formation required for membrane fusion is not resolved. Crystal structures of SM proteins alone and in complex with their cognate SNARE proteins have provided some insight, however, these structures lack the transmembrane spanning regions of the SNARE proteins and may not accurately reflect the native state. Here, we review the literature surrounding the regulatory role of mammalian Munc18 SM proteins required for exocytosis in eukaryotes. Our analysis suggests that the conflicting roles reported for these SM proteins may reflect differences in experimental design. SNARE proteins appear to require C-terminal immobilization or anchoring, for example through a transmembrane domain, to form a functional fusion complex in the presence of Munc18 proteins.
Collapse
Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Julia K. Archbold
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Suzanne J. Norwood
- Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Brett M. Collins
- Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| |
Collapse
|
36
|
Han GA, Park S, Bin NR, Jung CH, Kim B, Chandrasegaram P, Matsuda M, Riadi I, Han L, Sugita S. A pivotal role for pro-335 in balancing the dual functions of Munc18-1 domain-3a in regulated exocytosis. J Biol Chem 2014; 289:33617-28. [PMID: 25326390 DOI: 10.1074/jbc.m114.584805] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Munc18-1 plays essential dual roles in exocytosis: (i) stabilizing and trafficking the central SNARE protein, syntaxin-1 (i.e. chaperoning function), by its domain-1; and (ii) priming/stimulating exocytosis by its domain-3a. Here, we examine whether or not domain-3a also plays a significant role in the chaperoning of syntaxin-1 and, if so, how these dual functions of domain-3a are regulated. We demonstrate that introduction of quintuple mutations (K332E/K333E/P335A/Q336A/Y337L) in domain-3a of Munc18-1 abolishes its ability to bind syntaxin-1 and fails to rescue the level and trafficking of syntaxin-1 as well as to restore exocytosis in Munc18-1/2 double knockdown cells. By contrast, a quadruple mutant (K332E/K333E/Q336A/Y337L) sparing the Pro-335 residue retains all of these capabilities. A single point mutant of P335A reduces the ability to bind syntaxin-1 and rescue syntaxin-1 levels. Nonetheless, it surprisingly outperforms the wild type in the rescue of exocytosis. However, when additional mutations in the neighboring residues are combined with P335A mutation (K332E/K333E/P335A, P335A/Q336A/Y337L), the ability of the Munc18-1 variants to chaperone syntaxin-1 and to rescue exocytosis is strongly impaired. Our results indicate that residues from Lys-332 to Tyr-337 of domain-3a are intimately tied to the chaperoning function of Munc18-1. We also propose that Pro-335 plays a pivotal role in regulating the balance between the dual functions of domain-3a. The hinged conformation of the α-helix containing Pro-335 promotes the syntaxin-1 chaperoning function, whereas the P335A mutation promotes its priming function by facilitating the α-helix to adopt an extended conformation.
Collapse
Affiliation(s)
- Gayoung Anna Han
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Seungmee Park
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Na-Ryum Bin
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Chang Hun Jung
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Byungjin Kim
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Prashanth Chandrasegaram
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Maiko Matsuda
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Indira Riadi
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Liping Han
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Shuzo Sugita
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| |
Collapse
|
37
|
Martin S, Papadopulos A, Tomatis VM, Sierecki E, Malintan NT, Gormal RS, Giles N, Johnston WA, Alexandrov K, Gambin Y, Collins BM, Meunier FA. Increased polyubiquitination and proteasomal degradation of a Munc18-1 disease-linked mutant causes temperature-sensitive defect in exocytosis. Cell Rep 2014; 9:206-218. [PMID: 25284778 DOI: 10.1016/j.celrep.2014.08.059] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 07/31/2014] [Accepted: 08/23/2014] [Indexed: 12/23/2022] Open
Abstract
Munc18-1 is a critical component of the core machinery controlling neuroexocytosis. Recently, mutations in Munc18-1 leading to the development of early infantile epileptic encephalopathy have been discovered. However, which degradative pathway controls Munc18-1 levels and how it impacts on neuroexocytosis in this pathology is unknown. Using neurosecretory cells deficient in Munc18, we show that a disease-linked mutation, C180Y, renders the protein unstable at 37°C. Although the mutated protein retains its function as t-SNARE chaperone, neuroexocytosis is impaired, a defect that can be rescued at a lower permissive temperature. We reveal that Munc18-1 undergoes K48-linked polyubiquitination, which is highly increased by the mutation, leading to proteasomal, but not lysosomal, degradation. Our data demonstrate that functional Munc18-1 levels are controlled through polyubiquitination and proteasomal degradation. The C180Y disease-causing mutation greatly potentiates this degradative pathway, rendering Munc18-1 unable to facilitate neuroexocytosis, a phenotype that is reversed at a permissive temperature.
Collapse
Affiliation(s)
- Sally Martin
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
| | - Andreas Papadopulos
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Vanesa M Tomatis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Emma Sierecki
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Nancy T Malintan
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Rachel S Gormal
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Nichole Giles
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Wayne A Johnston
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Kirill Alexandrov
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yann Gambin
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Brett M Collins
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Frederic A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia.
| |
Collapse
|
38
|
Hellewell AL, Foresti O, Gover N, Porter MY, Hewitt EW. Analysis of familial hemophagocytic lymphohistiocytosis type 4 (FHL-4) mutant proteins reveals that S-acylation is required for the function of syntaxin 11 in natural killer cells. PLoS One 2014; 9:e98900. [PMID: 24910990 PMCID: PMC4049605 DOI: 10.1371/journal.pone.0098900] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 05/08/2014] [Indexed: 11/25/2022] Open
Abstract
Natural killer (NK) cell secretory lysosome exocytosis and cytotoxicity are impaired in familial hemophagocytic lymphohistiocytosis type 4 (FHL-4), a disorder caused by mutations in the gene encoding the SNARE protein syntaxin 11. We show that syntaxin 11 binds to SNAP23 in NK cells and that this interaction is reduced by FHL-4 truncation and frameshift mutation proteins that delete all or part of the SNARE domain of syntaxin 11. In contrast the FHL-4 mutant proteins bound to the Sec-1/Munc18-like (SM) protein Munc18-2. We demonstrate that the C-terminal cysteine rich region of syntaxin 11, which is deleted in the FHL-4 mutants, is S-acylated. This posttranslational modification is required for the membrane association of syntaxin 11 and for its polarization to the immunological synapse in NK cells conjugated to target cells. Moreover, we show that Munc18-2 is recruited by syntaxin 11 to intracellular membranes in resting NK cells and to the immunological synapse in activated NK cells. This recruitment of Munc18-2 is abolished by deletion of the C-terminal cysteine rich region of syntaxin 11. These results suggest a pivotal role for S-acylation in the function of syntaxin 11 in NK cells.
Collapse
Affiliation(s)
- Andrew L. Hellewell
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Ombretta Foresti
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Nicola Gover
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Morwenna Y. Porter
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Eric W. Hewitt
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
- * E-mail:
| |
Collapse
|
39
|
Parisotto D, Pfau M, Scheutzow A, Wild K, Mayer MP, Malsam J, Sinning I, Söllner TH. An extended helical conformation in domain 3a of Munc18-1 provides a template for SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex assembly. J Biol Chem 2014; 289:9639-50. [PMID: 24532794 DOI: 10.1074/jbc.m113.514273] [Citation(s) in RCA: 94] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Munc18-1, a SEC1/Munc18 protein and key regulatory protein in synaptic transmission, can either promote or inhibit SNARE complex assembly. Although the binary inhibitory interaction between Munc18-1 and closed syntaxin 1 is well described, the mechanism of how Munc18-1 stimulates membrane fusion remains elusive. Using a reconstituted assay that resolves vesicle docking, priming, clamping, and fusion during synaptic exocytosis, we show that helix 12 in domain 3a of Munc18-1 stimulates SNAREpin assembly and membrane fusion. A single point mutation (L348R) within helix 12 selectively abolishes VAMP2 binding and the stimulatory function of Munc18-1 in membrane fusion. In contrast, targeting a natural switch site (P335A) at the start of helix 12, which can result in an extended α-helical conformation, further accelerates lipid-mixing. Together with structural modeling, the data suggest that helix 12 provides a folding template for VAMP2, accelerating SNAREpin assembly and membrane fusion. Analogous SEC1/Munc18-SNARE interactions at other transport steps may provide a general mechanism to drive lipid bilayer merger. At the neuronal synapse, Munc18-1 may convert docked synaptic vesicles into a readily releasable pool.
Collapse
Affiliation(s)
- Daniel Parisotto
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany and
| | | | | | | | | | | | | | | |
Collapse
|
40
|
Secretagogue stimulation of neurosecretory cells elicits filopodial extensions uncovering new functional release sites. J Neurosci 2014; 33:19143-53. [PMID: 24305811 DOI: 10.1523/jneurosci.2634-13.2013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Regulated exocytosis in neurosecretory cells relies on the timely fusion of secretory granules (SGs) with the plasma membrane. Secretagogue stimulation leads to an enlargement of the cell footprint (surface area in contact with the coverslip), an effect previously attributed to exocytic fusion of SGs with the plasma membrane. Using total internal reflection fluorescence microscopy, we reveal the formation of filopodia-like structures in bovine chromaffin and PC12 cells driving the footprint expansion, suggesting the involvement of cortical actin network remodeling in this process. Using exocytosis-incompetent PC12 cells, we demonstrate that footprint enlargement is largely independent of SG fusion, suggesting that vesicular exocytic fusion plays a relatively minor role in filopodial expansion. The footprint periphery, including filopodia, undergoes extensive F-actin remodeling, an effect abolished by the actomyosin inhibitors cytochalasin D and blebbistatin. Imaging of both Lifeact-GFP and the SG marker protein neuropeptide Y-mCherry reveals that SGs actively translocate along newly forming actin tracks before undergoing fusion. Together, these data demonstrate that neurosecretory cells regulate the number of SGs undergoing exocytosis during sustained stimulation by controlling vesicular mobilization and translocation to the plasma membrane through actin remodeling. Such remodeling facilitates the de novo formation of fusion sites.
Collapse
|
41
|
Martin S, Tomatis VM, Papadopulos A, Christie MP, Malintan NT, Gormal RS, Sugita S, Martin JL, Collins BM, Meunier FA. The Munc18-1 domain 3a loop is essential for neuroexocytosis but not for syntaxin-1A transport to the plasma membrane. J Cell Sci 2013; 126:2353-60. [PMID: 23761923 DOI: 10.1242/jcs.126813] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Munc18-1 plays a dual role in transporting syntaxin-1A (Sx1a) to the plasma membrane and regulating SNARE-mediated membrane fusion. As impairment of either function leads to a common exocytic defect, assigning specific roles for various Munc18-1 domains has proved difficult. Structural analyses predict that a loop region in Munc18-1 domain 3a could catalyse the conversion of Sx1a from a 'closed', fusion-incompetent to an 'open', fusion-competent conformation. As this conversion occurs at the plasma membrane, mutations in this loop could potentially separate the chaperone and exocytic functions of Munc18-1. Expression of a Munc18-1 deletion mutant lacking 17 residues of the domain 3a loop (Munc18-1(Δ317-333)) in PC12 cells deficient in endogenous Munc18 (DKD-PC12 cells) fully rescued transport of Sx1a to the plasma membrane, but not exocytic secretory granule fusion. In vitro binding of Munc18-1(Δ317-333) to Sx1a was indistinguishable from that of full-length Munc18-1, consistent with the critical role of the closed conformation in Sx1a transport. However, in DKD-PC12 cells, Munc18-1(Δ317-333) binding to Sx1a was greatly reduced compared to that of full-length Munc18-1, suggesting that closed conformation binding contributes little to the overall interaction at the cell surface. Furthermore, we found that Munc18-1(Δ317-333) could bind SNARE complexes in vitro, suggesting that additional regulatory factors underpin the exocytic function of Munc18-1 in vivo. Together, these results point to a defined role for Munc18-1 in facilitating exocytosis linked to the loop region of domain 3a that is clearly distinct from its function in Sx1a transport.
Collapse
Affiliation(s)
- Sally Martin
- Queensland Brain Institute, The University of Queensland, Brisbane QLD 4072, Australia
| | | | | | | | | | | | | | | | | | | |
Collapse
|
42
|
Chua JJE, Jahn R, Klopfenstein DR. Managing intracellular transport. WORM 2013; 2:e21564. [PMID: 24058857 PMCID: PMC3670458 DOI: 10.4161/worm.21564] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 07/18/2012] [Accepted: 07/20/2012] [Indexed: 11/19/2022]
Abstract
Formation and normal function of neuronal synapses are intimately dependent on the delivery to and removal of biological materials from synapses by the intracellular transport machinery. Indeed, defects in intracellular transport contribute to the development and aggravation of neurodegenerative disorders. Despite its importance, regulatory mechanisms underlying this machinery remain poorly defined. We recently uncovered a phosphorylation-regulated mechanism that controls FEZ1-mediated Kinesin-1-based delivery of Stx1 into neuronal axons. Using C. elegans as a model organism to investigate transport defects, we show that FEZ1 mutations resulted in abnormal Stx1 aggregation in neuronal cell bodies and axons. This phenomenon closely resembles transport defects observed in neurodegenerative disorders. Importantly, diminished transport due to mutations of FEZ1 and Kinesin-1 were concomitant with increased accumulation of autophagosomes. Here, we discuss the significance of our findings in a broader context in relation to regulation of Kinesin-mediated transport and neurodegenerative disorders.
Collapse
Affiliation(s)
- John J E Chua
- Department of Neurobiology; Max-Planck-Institute for Biophysical Chemistry; Germany
| | | | | |
Collapse
|
43
|
Lam PP, Ohno M, Dolai S, He Y, Qin T, Liang T, Zhu D, Kang Y, Liu Y, Kauppi M, Xie L, Wan WC, Bin NR, Sugita S, Olkkonen VM, Takahashi N, Kasai H, Gaisano HY. Munc18b is a major mediator of insulin exocytosis in rat pancreatic β-cells. Diabetes 2013; 62:2416-28. [PMID: 23423569 PMCID: PMC3712044 DOI: 10.2337/db12-1380] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Sec1/Munc18 proteins facilitate the formation of trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes that mediate fusion of secretory granule (SG) with plasma membrane (PM). The capacity of pancreatic β-cells to exocytose insulin becomes compromised in diabetes. β-Cells express three Munc18 isoforms of which the role of Munc18b is unknown. We found that Munc18b depletion in rat islets disabled SNARE complex formation formed by syntaxin (Syn)-2 and Syn-3. Two-photon imaging analysis revealed in Munc18b-depleted β-cells a 40% reduction in primary exocytosis (SG-PM fusion) and abrogation of almost all sequential SG-SG fusion, together accounting for a 50% reduction in glucose-stimulated insulin secretion (GSIS). In contrast, gain-of-function expression of Munc18b wild-type and, more so, dominant-positive K314L/R315L mutant promoted the assembly of cognate SNARE complexes, which caused potentiation of biphasic GSIS. We found that this was attributed to a more than threefold enhancement of both primary exocytosis and sequential SG-SG fusion, including long-chain fusion (6-8 SGs) not normally (2-3 SG fusion) observed. Thus, Munc18b-mediated exocytosis may be deployed to increase secretory efficiency of SGs in deeper cytosolic layers of β-cells as well as additional primary exocytosis, which may open new avenues of therapy development for diabetes.
Collapse
Affiliation(s)
- Patrick P.L. Lam
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Mitsuyo Ohno
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Tokyo, Japan
| | - Subhankar Dolai
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yu He
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tairan Qin
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Dan Zhu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Youhou Kang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yunfeng Liu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Maria Kauppi
- National Institute for Health and Welfare, Biomedicum, Helsinki, Finland
| | - Li Xie
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Wilson C.Y. Wan
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Na-Rhum Bin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Division of Fundamental Neurobiology, University Health Network, Toronto, Ontario, Canada
| | - Shuzo Sugita
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Division of Fundamental Neurobiology, University Health Network, Toronto, Ontario, Canada
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum, Helsinki, Finland
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Tokyo, Japan
| | - Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Tokyo, Japan
- Corresponding authors: Haruo Kasai, , and Herbert Y. Gaisano,
| | - Herbert Y. Gaisano
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Corresponding authors: Haruo Kasai, , and Herbert Y. Gaisano,
| |
Collapse
|
44
|
Parsaud L, Li L, Jung CH, Park S, Saw NMN, Park S, Kim MY, Sugita S. Calcium-dependent activator protein for secretion 1 (CAPS1) binds to syntaxin-1 in a distinct mode from Munc13-1. J Biol Chem 2013; 288:23050-63. [PMID: 23801330 DOI: 10.1074/jbc.m113.494088] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium-dependent activator protein for secretion 1 (CAPS1) is a multidomain protein containing a Munc13 homology domain 1 (MHD1). Although CAPS1 and Munc13-1 play crucial roles in the priming stage of secretion, their functions are non-redundant. Similar to Munc13-1, CAPS1 binds to syntaxin-1, a key t-SNARE protein in neurosecretion. However, whether CAPS1 interacts with syntaxin-1 in a similar mode to Munc13-1 remains unclear. Here, using yeast two-hybrid assays followed by biochemical binding experiments, we show that the region in CAPS1 consisting of the C-terminal half of the MHD1 with the corresponding C-terminal region can bind to syntaxin-1. Importantly, the binding mode of CAPS1 to syntaxin-1 is distinct from that of Munc13-1; CAPS1 binds to the full-length of cytoplasmic syntaxin-1 with preference to its "open" conformation, whereas Munc13-1 binds to the first 80 N-terminal residues of syntaxin-1. Unexpectedly, the majority of the MHD1 of CAPS1 is dispensable, whereas the C-terminal 69 residues are crucial for the binding to syntaxin-1. Functionally, a C-terminal truncation of 69 or 134 residues in CAPS1 abolishes its ability to reconstitute secretion in permeabilized PC12 cells. Our results reveal a novel mode of binding between CAPS1 and syntaxin-1, which play a crucial role in neurosecretion. We suggest that the distinct binding modes between CAPS1 and Munc13-1 can account for their non-redundant functions in neurosecretion. We also propose that the preferential binding of CAPS1 to open syntaxin-1 can contribute to the stabilization of the open state of syntaxin-1 during its transition from "closed" state to the SNARE complex formation.
Collapse
Affiliation(s)
- Leon Parsaud
- Division of Fundamental Neurobiology, University Health Network, Toronto, Ontario M5T 2S8, Canada
| | | | | | | | | | | | | | | |
Collapse
|
45
|
Han GA, Bin NR, Kang SYA, Han L, Sugita S. Domain 3a of Munc18-1 plays a crucial role at the priming stage of exocytosis. J Cell Sci 2013; 126:2361-71. [PMID: 23525015 DOI: 10.1242/jcs.126862] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Munc18-1 is believed to prime or stimulate SNARE-mediated membrane fusion/exocytosis through binding to the SNARE complex, in addition to chaperoning its cognate syntaxins. Nevertheless, a Munc18-1 mutant that selectively loses the priming function while retaining the syntaxin chaperoning activity has not been identified. As a consequence, the mechanism that mediates Munc18-1-dependent priming remains unclear. In the course of analyzing the functional outcomes of a variety of point mutations in domain 3a of Munc18-1, we discovered insertion mutants (K332E/K333E with insertions of 5 or 39 residues). These mutants completely lose their ability to rescue secretion whereas they effectively restore syntaxin-1 expression at the plasma membrane as well as dense-core vesicle docking in Munc18-1 and Munc18-2 double-knockdown PC12 cells. The mutants can bind syntaxin-1A in a stoichiometric manner. However, binding to the SNARE complex is impaired compared with the wild type or the hydrophobic pocket mutant (F115E). Our results suggest that the domain 3a of Munc18-1 plays a crucial role in priming of exocytosis, which is independent of its syntaxin-1 chaperoning activity and is downstream of dense-core vesicle docking. We also suggest that the priming mechanism of Munc18-1 involves its domain-3a-dependent interaction with the SNARE complex.
Collapse
Affiliation(s)
- Gayoung Anna Han
- Division of Fundamental Neurobiology, University Health Network, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada
| | | | | | | | | |
Collapse
|
46
|
Wu Z, MacNeil AJ, Berman JN, Lin TJ. Syntaxin binding protein 1 is not required for allergic inflammation via IgE-mediated mast cell activation. PLoS One 2013; 8:e58560. [PMID: 23484036 PMCID: PMC3590206 DOI: 10.1371/journal.pone.0058560] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2012] [Accepted: 02/05/2013] [Indexed: 11/18/2022] Open
Abstract
Mast cells play a central role in both innate and acquired immunity. When activated by IgE-dependent FcεRI cross-linking, mast cells rapidly initiate a signaling cascade and undergo an extensive release of their granule contents, including inflammatory mediators. Some SNARE (soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor) proteins and SM (Sec1/Munc18) family proteins are involved in mast cell degranulation. However, the function of syntaxin binding protein 1 (STXBP1), a member of SM family, in mast cell degranulation is currently unknown. In this study, we examined the role of STXBP1 in IgE-dependent mast cell activation. Liver-derived mast cells (LMCs) from wild-type and STXBP1-deficient mice were cultured in vitro for the study of mast cell maturation, degranulation, cytokine and chemokine production, as well as MAPK, IκB-NFκB, and NFAT signaling pathways. In addition, in vivo models of passive cutaneous anaphylaxis and late-phase IgE-dependent inflammation were conducted in mast cell deficient W(sh) mice that had been reconstituted with wild-type or STXBP1-deficient mast cells. Our findings indicate that STXBP1 is not required for any of these important functional mechanisms in mast cells both in vitro and in vivo. Our results demonstrate that STXBP1 is dispensable during IgE-mediated mast cell activation and in IgE-dependent allergic inflammatory reactions.
Collapse
Affiliation(s)
- Zhengli Wu
- Department of Microbiology and Immunology and Department of Pediatrics, Dalhousie University and IWK Health Centre, Halifax, Nova Scotia, Canada
| | - Adam J. MacNeil
- Department of Microbiology and Immunology and Department of Pediatrics, Dalhousie University and IWK Health Centre, Halifax, Nova Scotia, Canada
| | - Jason N. Berman
- Department of Microbiology and Immunology and Department of Pediatrics, Dalhousie University and IWK Health Centre, Halifax, Nova Scotia, Canada
| | - Tong-Jun Lin
- Department of Microbiology and Immunology and Department of Pediatrics, Dalhousie University and IWK Health Centre, Halifax, Nova Scotia, Canada
| |
Collapse
|
47
|
Crucial role of the hydrophobic pocket region of Munc18 protein in mast cell degranulation. Proc Natl Acad Sci U S A 2013; 110:4610-5. [PMID: 23487749 DOI: 10.1073/pnas.1214887110] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The function of the Munc18-1 protein hydrophobic pocket, which interacts with the syntaxin-1 N-terminal peptide, has been highly controversial in neurosecretion. Recent analysis of patients with familial hemophagocytic lymphohistiocytosis type 5 has identified the E132A mutation in the hydrophobic pocket of Munc18-2, prompting us to examine the role of this region in the context of immune cell secretion. Double knockdown of Munc18-1 and Munc18-2 in RBL-2H3 mast cells eliminates both IgE-dependent and ionomycin-induced degranulation and causes a significant reduction in syntaxin-11 without altering expressions of the other syntaxin isoforms examined. These phenotypes were effectively rescued on reexpression of wild-type Munc18-1 or Munc18-2 but not the mutants (F115E, E132A, and F115E/E132A) in the hydrophobic pocket of Munc18. In addition, these mutants show that they are unable to directly interact with syntaxin-11, as tested through protein interaction experiments. Our results demonstrate the crucial roles of the hydrophobic pocket of Munc18 in mast cell degranulation, which include the regulation of syntaxin-11. We also suggest that the functional importance of this region is significantly different between neuronal and immune cell exocytosis.
Collapse
|
48
|
Rizo J, Südhof TC. The Membrane Fusion Enigma: SNAREs, Sec1/Munc18 Proteins, and Their Accomplices—Guilty as Charged? Annu Rev Cell Dev Biol 2012; 28:279-308. [DOI: 10.1146/annurev-cellbio-101011-155818] [Citation(s) in RCA: 318] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390;
| | - Thomas C. Südhof
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305;
| |
Collapse
|
49
|
Park JH, Jung MS, Kim YS, Song WJ, Chung SH. Phosphorylation of Munc18-1 by Dyrk1A regulates its interaction with Syntaxin 1 and X11α. J Neurochem 2012; 122:1081-91. [PMID: 22765017 DOI: 10.1111/j.1471-4159.2012.07861.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Dual-specificity tyrosine(Y)-phosphorylation-regulated kinase 1A (Dyrk1A) is a protein kinase that might be responsible for mental retardation and early onset of Alzheimer's disease in Down's syndrome patients. Dyrk1A plays a role in many cellular pathways through phosphorylation of diverse substrate proteins; however, its role in synaptic vesicle exocytosis is poorly understood. Munc18-1, a central regulator of neurotransmitter release, interacts with Syntaxin 1 and X11α. Syntaxin 1 is a key soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein involved in synaptic vesicle docking/fusion events, and X11α modulates amyloid precursor protein processing and β amyloid generation. In this study, we demonstrate that Dyrk1A interacts with and phosphorylates Munc18-1 at the Thr(479) residue. The phosphorylation of Munc18-1 at Thr(479) by Dyrk1A stimulated binding of Munc18-1 to Syntaxin 1 and X11α. Furthermore, the levels of phospho-Thr(479) -Munc18-1 were enhanced in the brains of transgenic mice over-expressing Dyrk1A protein, providing in vivo evidence of Munc18-1 phosphorylation by Dyrk1A. These results reveal a link between Munc18-1 and Dyrk1A in synaptic vesicle trafficking and amyloid precursor protein processing, suggesting that up-regulated Dyrk1A in Down's syndrome and Alzheimer's disease brains may contribute to some pathological features, including synaptic dysfunction and cognitive defect through abnormal phosphorylation of Munc18-1.
Collapse
Affiliation(s)
- Jung-Hwa Park
- Graduate Program in Neuroscience, Institute for Brain Science and Technology (IBST), FIRST Research Group, Inje University, Busan, South Korea
| | | | | | | | | |
Collapse
|
50
|
Neurotransmitter release mechanisms studied in Caenorhabditis elegans. Cell Calcium 2012; 52:289-95. [DOI: 10.1016/j.ceca.2012.03.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Revised: 03/19/2012] [Accepted: 03/25/2012] [Indexed: 01/15/2023]
|