151
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Gruget C, Coleman J, Bello O, Krishnakumar SS, Perez E, Rothman JE, Pincet F, Donaldson SH. Rearrangements under confinement lead to increased binding energy of Synaptotagmin‐1 with anionic membranes in Mg
2+
and Ca
2+. FEBS Lett 2018; 592:1497-1506. [DOI: 10.1002/1873-3468.13040] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 03/05/2018] [Accepted: 03/16/2018] [Indexed: 11/09/2022]
Affiliation(s)
- Clémence Gruget
- Laboratoire de Physique Statistique Ecole Normale Supérieure PSL Research University Paris France
| | - Jeff Coleman
- Department of Cell Biology Yale University School of Medicine New Haven CT USA
| | - Oscar Bello
- Department of Clinical and Experimental Epilepsy Institute of Neurology University College London UK
| | - Shyam S. Krishnakumar
- Department of Cell Biology Yale University School of Medicine New Haven CT USA
- Department of Clinical and Experimental Epilepsy Institute of Neurology University College London UK
| | - Eric Perez
- Laboratoire de Physique Statistique Ecole Normale Supérieure PSL Research University Paris France
| | - James E. Rothman
- Department of Cell Biology Yale University School of Medicine New Haven CT USA
- Department of Clinical and Experimental Epilepsy Institute of Neurology University College London UK
| | - Frederic Pincet
- Laboratoire de Physique Statistique Ecole Normale Supérieure PSL Research University Paris France
- Department of Cell Biology Yale University School of Medicine New Haven CT USA
| | - Stephen H. Donaldson
- Département de Physique Ecole Normale Supérieure PSL Research University, CNRS Paris France
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152
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Liang B, Tamm LK. Solution NMR of SNAREs, complexin and α-synuclein in association with membrane-mimetics. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2018; 105:41-53. [PMID: 29548366 PMCID: PMC5863748 DOI: 10.1016/j.pnmrs.2018.02.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Revised: 02/06/2018] [Accepted: 02/06/2018] [Indexed: 06/08/2023]
Abstract
SNARE-mediated membrane fusion is a ubiquitous process responsible for intracellular vesicle trafficking, including membrane fusion in exocytosis that leads to hormone and neurotransmitter release. The proteins that facilitate this process are highly dynamic and adopt multiple conformations when they interact with other proteins and lipids as they form highly regulated molecular machines that operate on membranes. Solution NMR is an ideal method to capture high-resolution glimpses of the molecular transformations that take place when these proteins come together and work on membranes. Since solution NMR has limitations on the size of proteins and complexes that can be studied, lipid bilayer model membranes cannot be used in these approaches, so the relevant interactions are typically studied in various types of membrane-mimetics that are tractable by solution NMR methods. In this review we therefore first summarize different membrane-mimetic systems that are commonly used or that show promise for solution NMR studies of membrane-interacting proteins. We then summarize recent NMR studies on two SNARE proteins, syntaxin and synaptobrevin, and two related regulatory proteins, complexin and α-synuclein, and their interactions with membrane lipids. These studies provide a structural and dynamical framework for how these proteins might carry out their functions in the vicinity of lipid membranes. The common theme throughout these studies is that membrane interactions have major influences on the structural dynamics of these proteins that cannot be ignored when attempting to explain their functions in contemporary models of SNARE-mediated membrane fusion.
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Affiliation(s)
- Binyong Liang
- Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
| | - Lukas K Tamm
- Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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153
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Barnes CO, Gristick HB, Freund NT, Escolano A, Lyubimov AY, Hartweger H, West AP, Cohen AE, Nussenzweig MC, Bjorkman PJ. Structural characterization of a highly-potent V3-glycan broadly neutralizing antibody bound to natively-glycosylated HIV-1 envelope. Nat Commun 2018; 9:1251. [PMID: 29593217 PMCID: PMC5871869 DOI: 10.1038/s41467-018-03632-y] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 03/01/2018] [Indexed: 01/16/2023] Open
Abstract
Broadly neutralizing antibodies (bNAbs) isolated from HIV-1-infected individuals inform HIV-1 vaccine design efforts. Developing bNAbs with increased efficacy requires understanding how antibodies interact with the native oligomannose and complex-type N-glycan shield that hides most protein epitopes on HIV-1 envelope (Env). Here we present crystal structures, including a 3.8-Å X-ray free electron laser dataset, of natively glycosylated Env trimers complexed with BG18, the most potent V3/N332gp120 glycan-targeting bNAb reported to date. Our structures show conserved contacts mediated by common D gene-encoded residues with the N332gp120 glycan and the gp120 GDIR peptide motif, but a distinct Env-binding orientation relative to PGT121/10-1074 bNAbs. BG18's binding orientation provides additional contacts with N392gp120 and N386gp120 glycans near the V3-loop base and engages protein components of the V1-loop. The BG18-natively-glycosylated Env structures facilitate understanding of bNAb-glycan interactions critical for using V3/N332gp120 bNAbs therapeutically and targeting their epitope for immunogen design.
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Affiliation(s)
- Christopher O Barnes
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Harry B Gristick
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Natalia T Freund
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY, 10065, USA
- Department of Clinical Immunology and Microbiology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel
| | - Amelia Escolano
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY, 10065, USA
| | - Artem Y Lyubimov
- Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - Harald Hartweger
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY, 10065, USA
| | - Anthony P West
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Aina E Cohen
- Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - Michel C Nussenzweig
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY, 10065, USA
- Howard Hughes Medical Institute, The Rockefeller University, New York, NY, 10065, USA
| | - Pamela J Bjorkman
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.
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154
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Kou X, Xu X, Chen C, Sanmillan ML, Cai T, Zhou Y, Giraudo C, Le A, Shi S. The Fas/Fap-1/Cav-1 complex regulates IL-1RA secretion in mesenchymal stem cells to accelerate wound healing. Sci Transl Med 2018; 10:eaai8524. [PMID: 29540618 PMCID: PMC6310133 DOI: 10.1126/scitranslmed.aai8524] [Citation(s) in RCA: 119] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 03/06/2017] [Accepted: 02/13/2018] [Indexed: 12/16/2022]
Abstract
Mesenchymal stem cells (MSCs) are capable of secreting exosomes, extracellular vesicles, and cytokines to regulate cell and tissue homeostasis. However, it is unknown whether MSCs use a specific exocytotic fusion mechanism to secrete exosomes and cytokines. We show that Fas binds with Fas-associated phosphatase-1 (Fap-1) and caveolin-1 (Cav-1) to activate a common soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor (SNARE)-mediated membrane fusion mechanism to release small extracellular vesicles (sEVs) in MSCs. Moreover, we reveal that MSCs produce and secrete interleukin-1 receptor antagonist (IL-1RA) associated with sEVs to maintain rapid wound healing in the gingiva via the Fas/Fap-1/Cav-1 cascade. Tumor necrosis factor-α (TNF-α) serves as an activator to up-regulate Fas and Fap-1 expression via the nuclear factor κB pathway to promote IL-1RA release. This study identifies a previously unknown Fas/Fap-1/Cav-1 axis that regulates SNARE-mediated sEV and IL-1RA secretion in stem cells, which contributes to accelerated wound healing.
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Affiliation(s)
- Xiaoxing Kou
- Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA
- Department of Orthodontics, Peking University School and Hospital of Stomatology, #22 Zhongguancun South Avenue, Beijing 100081, China
| | - Xingtian Xu
- Center for Craniofacial Molecular Biology, Ostrow School of Dentistry, University of Southern California, 2250 Alcazar Street, CSA 103, Los Angeles, CA 90033, USA
| | - Chider Chen
- Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA
| | - Maria Laura Sanmillan
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Tao Cai
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20982, USA
| | - Yanheng Zhou
- Department of Orthodontics, Peking University School and Hospital of Stomatology, #22 Zhongguancun South Avenue, Beijing 100081, China
| | - Claudio Giraudo
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Anh Le
- Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA
| | - Songtao Shi
- Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104, USA.
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155
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Houy S, Groffen AJ, Ziomkiewicz I, Verhage M, Pinheiro PS, Sørensen JB. Doc2B acts as a calcium sensor for vesicle priming requiring synaptotagmin-1, Munc13-2 and SNAREs. eLife 2017; 6:27000. [PMID: 29274147 PMCID: PMC5758110 DOI: 10.7554/elife.27000] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Accepted: 12/21/2017] [Indexed: 01/08/2023] Open
Abstract
Doc2B is a cytosolic protein with binding sites for Munc13 and Tctex-1 (dynein light chain), and two C2-domains that bind to phospholipids, Ca2+ and SNAREs. Whether Doc2B functions as a calcium sensor akin to synaptotagmins, or in other calcium-independent or calcium-dependent capacities is debated. We here show by mutation and overexpression that Doc2B plays distinct roles in two sequential priming steps in mouse adrenal chromaffin cells. Mutating Ca2+-coordinating aspartates in the C2A-domain localizes Doc2B permanently at the plasma membrane, and renders an upstream priming step Ca2+-independent, whereas a separate function in downstream priming depends on SNARE-binding, Ca2+-binding to the C2B-domain of Doc2B, interaction with ubMunc13-2 and the presence of synaptotagmin-1. Another function of Doc2B – inhibition of release during sustained calcium elevations – depends on an overlapping protein domain (the MID-domain), but is separate from its Ca2+-dependent priming function. We conclude that Doc2B acts as a vesicle priming protein.
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Affiliation(s)
- Sébastien Houy
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark
| | - Alexander J Groffen
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU Medical Center, Amsterdam, Netherlands
| | - Iwona Ziomkiewicz
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark.,Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Cambridge, United Kingdom
| | - Matthijs Verhage
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU Medical Center, Amsterdam, Netherlands.,Department of Functional Genomics, Faculty of Science, Center for Neurogenomics and Cognitive Research, VrijeUniversiteit, Amsterdam, Netherlands
| | - Paulo S Pinheiro
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark
| | - Jakob Balslev Sørensen
- Neuronal Secretion Group, Department of Neuroscience, University of Copenhagen, København, Denmark
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156
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Synaptotagmin-1 drives synchronous Ca 2+-triggered fusion by C 2B-domain-mediated synaptic-vesicle-membrane attachment. Nat Neurosci 2017; 21:33-40. [PMID: 29230057 PMCID: PMC5742540 DOI: 10.1038/s41593-017-0037-5] [Citation(s) in RCA: 101] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 10/14/2017] [Indexed: 12/19/2022]
Abstract
The synaptic vesicle (SV) protein Synaptotagmin-1 (Syt1) is the Ca2+ sensor for fast synchronous release. Biochemical and structural data suggest that Syt1 interacts with phospholipids and SNARE complex, but how these interactions translate into SV fusion remains poorly understood. Utilizing flash-and-freeze electron microscopy, which triggers action potentials (AP) with light and coordinately arrests synaptic structures with rapid freezing, we found synchronous release-impairing mutations in the Syt1 C2B domain (K325, 327; R398, 399) to also disrupt SV-active zone plasma membrane attachment. Single AP induction rescued membrane attachment in these mutants within <10ms through activation of the Syt1 Ca2+ binding site. The rapid SV membrane translocation temporarily correlates with resynchronization of release and paired pulse facilitation. Based on these findings, we redefine the role of Syt1 as part of Ca2+-dependent vesicle translocation machinery, and propose that Syt1 enables fast neurotransmitter release by means of its dynamic membrane attachment activities.
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157
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Armed for destruction: formation, function and trafficking of neutrophil granules. Cell Tissue Res 2017; 371:455-471. [PMID: 29185068 DOI: 10.1007/s00441-017-2731-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/02/2017] [Indexed: 12/21/2022]
Abstract
Neutrophils respond nearly instantly to infection, rapidly deploying a potent enzymatic and chemical arsenal immediately upon entering an infected site. This capacity for rapid and potent responses is endowed by stores of antimicrobial proteins contained in readily mobilizable granules. These granules contain the proteins necessary to mediate the recruitment, chemotaxis, antimicrobial function and NET formation of neutrophils. Four granule types exist, and are sequentially deployed as neutrophils enter infected sites. Secretory vesicles are released first, enabling recruitment of neutrophils out of the blood. Next, specific and gelatinase granules are released to enable neutrophil migration and begin the formation of an antimicrobial environment. Finally, azurophilic granules release potent antimicrobial proteins at the site of infection and into phagosomes. The step-wise mobilization of these granules is regulated by calcium signaling, while specific trafficking regulators and membrane fusion complexes ensure the delivery of granules to the correct subcellular site. In this review, we describe neutrophil granules from their formation through to their deployment at the site of infection, focusing on recent developments in our understanding of the signaling pathways and vesicular trafficking mechanisms which mediate neutrophil degranulation.
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158
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Use-dependent potentiation of voltage-gated calcium channels rescues neurotransmission in nerve terminals intoxicated by botulinum neurotoxin serotype A. Sci Rep 2017; 7:15862. [PMID: 29158500 PMCID: PMC5696531 DOI: 10.1038/s41598-017-16064-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 11/06/2017] [Indexed: 01/27/2023] Open
Abstract
Botulinum neurotoxins (BoNTs) are highly potent toxins that cleave neuronal SNARE proteins required for neurotransmission, causing flaccid paralysis and death by asphyxiation. Currently, there are no clinical treatments to delay or reverse BoNT-induced blockade of neuromuscular transmission. While aminopyridines have demonstrated varying efficacy in transiently reducing paralysis following BoNT poisoning, the precise mechanisms by which aminopyridines symptomatically treat botulism are not understood. Here we found that activity-dependent potentiation of presynaptic voltage-gated calcium channels (VGCCs) underlies 3,4-diaminopyridine (3,4-DAP)-mediated rescue of neurotransmission in central nervous system synapses and mouse diaphragm neuromuscular junctions fully intoxicated by BoNT serotype A. Combinatorial treatments with 3,4-DAP and VGCC agonists proved synergistic in restoring suprathreshold endplate potentials in mouse diaphragms fully intoxicated by BoNT/A. In contrast, synapses fully intoxicated by BoNT serotypes D or E were refractory to synaptic rescue by any treatment. We interpret these data to propose that increasing the duration or extent of VGCC activation prolongs the opportunity for low-efficiency fusion by fusogenic complexes incorporating BoNT/A-cleaved SNAP-25. The identification of VGCC agonists that rescue neurotransmission in BoNT/A-intoxicated synapses provides compelling evidence for potential therapeutic utility in some cases of human botulism.
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159
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Kim J, Shin YK. Productive and Non-productive Pathways for Synaptotagmin 1 to Support Ca 2+-Triggered Fast Exocytosis. Front Mol Neurosci 2017; 10:380. [PMID: 29187811 PMCID: PMC5695160 DOI: 10.3389/fnmol.2017.00380] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 11/01/2017] [Indexed: 12/17/2022] Open
Abstract
Ca2+-triggered SNARE-mediated membrane fusion is essential for neuronal communication. The speed of this process is of particular importance because it sets a time limit to cognitive and physical activities. In this work, we expand the proteoliposome-to-supported bilayer (SBL) fusion assay by successfully incorporating synaptotagmin 1 (Syt1), a major Ca2+ sensor. We report that Syt1 and Ca2+ together can elicit more than a 50-fold increase in the number of membrane fusion events when compared with membrane fusion mediated by SNAREs only. What is remarkable is that ~55% of all vesicle fusion events occurs within 20 ms upon vesicle docking. Furthermore, pre-binding of Syt1 to SNAREs prior to Ca2+ inhibits spontaneous fusion, but intriguingly, this leads to a complete loss of the Ca2+ responsiveness. Thus, our results suggest that there is a productive and a non-productive pathway for Syt1, depending on whether there is a premature interaction between Syt1 and SNAREs. Our results show that Ca2+ binding to Syt1 prior to Syt1's binding to SNAREs may be a prerequisite for the productive pathway. The successful reconstitution of Syt1 activities in the physiological time scale provides new opportunities to test the current mechanistic models for Ca2+-triggered exocytosis.
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Affiliation(s)
| | - Yeon-Kyun Shin
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, United States
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160
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The Dual Function of the Polybasic Juxtamembrane Region of Syntaxin 1A in Clamping Spontaneous Release and Stimulating Ca 2+-Triggered Release in Neuroendocrine Cells. J Neurosci 2017; 38:220-231. [PMID: 29133430 DOI: 10.1523/jneurosci.1541-17.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2017] [Revised: 09/07/2017] [Accepted: 10/07/2017] [Indexed: 11/21/2022] Open
Abstract
The exact function of the polybasic juxtamembrane region (5RK) of the plasma membrane neuronal SNARE, syntaxin 1A (Syx), in vesicle exocytosis, although widely studied, is currently not clear. Here, we addressed the role of 5RK in Ca2+-triggered release, using our Syx-based intramolecular fluorescence resonance energy transfer (FRET) probe, which previously allowed us to resolve a depolarization-induced Ca2+-dependent close-to-open transition (CDO) of Syx that occurs concomitant with evoked release, both in PC12 cells and hippocampal neurons and was abolished upon charge neutralization of 5RK. First, using dynamic FRET analysis in PC12 cells, we show that CDO occurs following assembly of SNARE complexes that include the vesicular SNARE, synaptobrevin 2, and that the participation of 5RK in CDO goes beyond its participation in the final zippering of the complex, because mutations of residues adjacent to 5RK, believed to be crucial for final zippering, do not abolish this transition. In addition, we show that CDO is contingent on membrane phosphatidylinositol 4,5-bisphosphate (PIP2), which is fundamental for maintaining regulated exocytosis, as depletion of membranal PIP2 abolishes CDO. Prompted by these results, which underscore a potentially significant role of 5RK in exocytosis, we next amperometrically analyzed catecholamine release from PC12 cells, revealing that charge neutralization of 5RK promotes spontaneous and inhibits Ca2+-triggered release events. Namely, 5RK acts as a fusion clamp, making release dependent on stimulation by Ca2+SIGNIFICANCE STATEMENT Syntaxin 1A (Syx) is a central protein component of the SNARE complex, which underlies neurotransmitter release. Although widely studied in relation to its participation in SNARE complex formation and its interaction with phosphoinositides, the function of Syx's polybasic juxtamembrane region (5RK) remains unclear. Previously, we showed that a conformational transition of Syx, related to calcium-triggered release, reported by a Syx-based FRET probe, is abolished upon charge neutralization of 5RK (5RK/A). Here we show that this conformational transition is dependent on phosphatidylinositol 4,5-bisphosphate (PIP2) and is related to SNARE complex formation. Subsequently, we show that the 5RK/A mutation enhances spontaneous release and inhibits calcium-triggered release in neuroendocrine cells, indicating a previously unrecognized role of 5RK in neurotransmitter release.
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161
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Rothman JE, Krishnakumar SS, Grushin K, Pincet F. Hypothesis - buttressed rings assemble, clamp, and release SNAREpins for synaptic transmission. FEBS Lett 2017; 591:3459-3480. [PMID: 28983915 PMCID: PMC5698743 DOI: 10.1002/1873-3468.12874] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 10/02/2017] [Accepted: 10/02/2017] [Indexed: 11/21/2022]
Abstract
Neural networks are optimized to detect temporal coincidence on the millisecond timescale. Here, we offer a synthetic hypothesis based on recent structural insights into SNAREs and the C2 domain proteins to explain how synaptic transmission can keep this pace. We suggest that an outer ring of up to six curved Munc13 ‘MUN’ domains transiently anchored to the plasma membrane via its flanking domains surrounds a stable inner ring comprised of synaptotagmin C2 domains to serve as a work‐bench on which SNAREpins are templated. This ‘buttressed‐ring hypothesis’ affords straightforward answers to many principal and long‐standing questions concerning how SNAREpins can be assembled, clamped, and then released synchronously with an action potential.
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Affiliation(s)
- James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Kirill Grushin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Frederic Pincet
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Laboratoire de Physique Statistique, Ecole Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris Cité, Sorbonne Universités UPMC Univ, CNRS, Paris, France
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162
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Walter AM, Müller R, Tawfik B, Wierda KD, Pinheiro PS, Nadler A, McCarthy AW, Ziomkiewicz I, Kruse M, Reither G, Rettig J, Lehmann M, Haucke V, Hille B, Schultz C, Sørensen JB. Phosphatidylinositol 4,5-bisphosphate optical uncaging potentiates exocytosis. eLife 2017; 6:30203. [PMID: 29068313 PMCID: PMC5711374 DOI: 10.7554/elife.30203] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 10/24/2017] [Indexed: 12/14/2022] Open
Abstract
Phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] is essential for exocytosis. Classical ways of manipulating PI(4,5)P2 levels are slower than its metabolism, making it difficult to distinguish effects of PI(4,5)P2 from those of its metabolites. We developed a membrane-permeant, photoactivatable PI(4,5)P2, which is loaded into cells in an inactive form and activated by light, allowing sub-second increases in PI(4,5)P2 levels. By combining this compound with electrophysiological measurements in mouse adrenal chromaffin cells, we show that PI(4,5)P2 uncaging potentiates exocytosis and identify synaptotagmin-1 (the Ca2+ sensor for exocytosis) and Munc13-2 (a vesicle priming protein) as the relevant effector proteins. PI(4,5)P2 activation of exocytosis did not depend on the PI(4,5)P2-binding CAPS-proteins, suggesting that PI(4,5)P2 uncaging may bypass CAPS-function. Finally, PI(4,5)P2 uncaging triggered the rapid fusion of a subset of readily-releasable vesicles, revealing a rapid role of PI(4,5)P2 in fusion triggering. Thus, optical uncaging of signaling lipids can uncover their rapid effects on cellular processes and identify lipid effectors. Cells in our body communicate by releasing compounds called transmitters that carry signals from one cell to the next. Packages called vesicles store transmitters within the signaling cell. When the cell needs to send a signal, the vesicles fuse with the cell's membrane and release their cargo. For many signaling processes, such as those used by neurons, this fusion is regulated, fast, and coupled to the signal that the cell receives to activate release. Specialized molecular machines made up of proteins and fatty acid molecules called signaling lipids enable this to happen. One signaling lipid called PI(4,5)P2 (short for phosphatidylinositol 4,5-bisphosphate) is essential for vesicle fusion as well as for other processes in cells. It interacts with several proteins that help it control fusion and the release of transmitter. While it is possible to study the role of these proteins using genetic tools to inactivate them, the signaling lipids are more difficult to manipulate. Existing methods result in slow changes in PI(4,5)P2 levels, making it hard to directly attribute later changes to PI(4,5)P2. Walter, Müller, Tawfik et al. developed a new method to measure how PI(4,5)P2 affects transmitter release in living mammalian cells, which causes a rapid increase in PI(4,5)P2 levels. The method uses a chemical compound called “caged PI(4,5)P2” that can be loaded into cells but remains undetected until ultraviolet light is shone on it. The ultraviolet light uncages the compound, generating active PI(4,5)P2 in less than one second. Walter et al. found that when they uncaged PI(4,5)P2 in this way, the amount of transmitter released by cells increased. Combining this with genetic tools, it was possible to investigate which proteins of the release machinery were required for this effect. The results suggest that two different types of proteins that interact with PI(4,5)P2 are needed: one must bind PI(4,5)P2 to carry out its role and the other helps PI(4,5)P2 accumulate at the site of vesicle fusion. The new method also allowed Walter et al. to show that a fast increase in PI(4,5)P2 triggers a subset of vesicles to fuse very rapidly. This shows that PI(4,5)P2 rapidly regulates the release of transmitter. Caged PI(4,5)P2 will be useful to study other processes in cells that need PI(4,5)P2, helping scientists understand more about how signaling lipids control many different events at cellular membranes.
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Affiliation(s)
- Alexander M Walter
- Neurosecretion group, Center for Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Rainer Müller
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Bassam Tawfik
- Neurosecretion group, Center for Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Keimpe Db Wierda
- Neurosecretion group, Center for Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Paulo S Pinheiro
- Neurosecretion group, Center for Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - André Nadler
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany.,Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Anthony W McCarthy
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Iwona Ziomkiewicz
- Neurosecretion group, Center for Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Discovery Sciences, AstraZeneca, Cambridge, United Kingdom
| | - Martin Kruse
- Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle, United States
| | - Gregor Reither
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Jens Rettig
- Cellular Neurophysiology, Center for Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Martin Lehmann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Volker Haucke
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Bertil Hille
- Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle, United States
| | - Carsten Schultz
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Jakob Balslev Sørensen
- Neurosecretion group, Center for Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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163
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Wu Z, Thiyagarajan S, O'Shaughnessy B, Karatekin E. Regulation of Exocytotic Fusion Pores by SNARE Protein Transmembrane Domains. Front Mol Neurosci 2017; 10:315. [PMID: 29066949 PMCID: PMC5641348 DOI: 10.3389/fnmol.2017.00315] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Accepted: 09/19/2017] [Indexed: 12/26/2022] Open
Abstract
Calcium-triggered exocytotic release of neurotransmitters and hormones from neurons and neuroendocrine cells underlies neuronal communication, motor activity and endocrine functions. The core of the neuronal exocytotic machinery is composed of soluble N-ethyl maleimide sensitive factor attachment protein receptors (SNAREs). Formation of complexes between vesicle-attached v- and plasma-membrane anchored t-SNAREs in a highly regulated fashion brings the membranes into close apposition. Small, soluble proteins called Complexins (Cpx) and calcium-sensing Synaptotagmins cooperate to block fusion at low resting calcium concentrations, but trigger release upon calcium increase. A growing body of evidence suggests that the transmembrane domains (TMDs) of SNARE proteins play important roles in regulating the processes of fusion and release, but the mechanisms involved are only starting to be uncovered. Here we review recent evidence that SNARE TMDs exert influence by regulating the dynamics of the fusion pore, the initial aqueous connection between the vesicular lumen and the extracellular space. Even after the fusion pore is established, hormone release by neuroendocrine cells is tightly controlled, and the same may be true of neurotransmitter release by neurons. The dynamics of the fusion pore can regulate the kinetics of cargo release and the net amount released, and can determine the mode of vesicle recycling. Manipulations of SNARE TMDs were found to affect fusion pore properties profoundly, both during exocytosis and in biochemical reconstitutions. To explain these effects, TMD flexibility, and interactions among TMDs or between TMDs and lipids have been invoked. Exocytosis has provided the best setting in which to unravel the underlying mechanisms, being unique among membrane fusion reactions in that single fusion pores can be probed using high-resolution methods. An important role will likely be played by methods that can probe single fusion pores in a biochemically defined setting which have recently become available. Finally, computer simulations are valuable mechanistic tools because they have the power to access small length scales and very short times that are experimentally inaccessible.
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Affiliation(s)
- Zhenyong Wu
- Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, CT, United States.,Nanobiology Institute, Yale University, West Haven, CT, United States
| | | | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, NY, United States
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, CT, United States.,Nanobiology Institute, Yale University, West Haven, CT, United States.,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States.,Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique (CNRS), Paris, France
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164
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Wickner W, Rizo J. A cascade of multiple proteins and lipids catalyzes membrane fusion. Mol Biol Cell 2017; 28:707-711. [PMID: 28292915 PMCID: PMC5349777 DOI: 10.1091/mbc.e16-07-0517] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 01/05/2017] [Accepted: 01/10/2017] [Indexed: 11/11/2022] Open
Abstract
Recent studies suggest revisions to the SNARE paradigm of membrane fusion. Membrane tethers and/or SNAREs recruit proteins of the Sec 1/Munc18 family to catalyze SNARE assembly into trans-complexes. SNARE-domain zippering draws the bilayers into immediate apposition and provides a platform to position fusion triggers such as Sec 17/α-SNAP and/or synaptotagmin, which insert their apolar "wedge" domains into the bilayers, initiating the lipid rearrangements of fusion.
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Affiliation(s)
- William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755 )
| | - Josep Rizo
- Departments of Biophysics, Biochemistry, and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390 )
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165
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Exceptionally tight membrane-binding may explain the key role of the synaptotagmin-7 C 2A domain in asynchronous neurotransmitter release. Proc Natl Acad Sci U S A 2017; 114:E8518-E8527. [PMID: 28923929 DOI: 10.1073/pnas.1710708114] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptotagmins (Syts) act as Ca2+ sensors in neurotransmitter release by virtue of Ca2+-binding to their two C2 domains, but their mechanisms of action remain unclear. Puzzlingly, Ca2+-binding to the C2B domain appears to dominate Syt1 function in synchronous release, whereas Ca2+-binding to the C2A domain mediates Syt7 function in asynchronous release. Here we show that crystal structures of the Syt7 C2A domain and C2AB region, and analyses of intrinsic Ca2+-binding to the Syt7 C2 domains using isothermal titration calorimetry, did not reveal major differences that could explain functional differentiation between Syt7 and Syt1. However, using liposome titrations under Ca2+ saturating conditions, we show that the Syt7 C2A domain has a very high membrane affinity and dominates phospholipid binding to Syt7 in the presence or absence of l-α-phosphatidylinositol 4,5-diphosphate (PIP2). For Syt1, the two Ca2+-saturated C2 domains have similar affinities for membranes lacking PIP2, but the C2B domain dominates binding to PIP2-containing membranes. Mutagenesis revealed that the dramatic differences in membrane affinity between the Syt1 and Syt7 C2A domains arise in part from apparently conservative residue substitutions, showing how striking biochemical and functional differences can result from the cumulative effects of subtle residue substitutions. Viewed together, our results suggest that membrane affinity may be a key determinant of the functions of Syt C2 domains in neurotransmitter release.
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166
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Lai Y, Choi UB, Leitz J, Rhee HJ, Lee C, Altas B, Zhao M, Pfuetzner RA, Wang AL, Brose N, Rhee J, Brunger AT. Molecular Mechanisms of Synaptic Vesicle Priming by Munc13 and Munc18. Neuron 2017; 95:591-607.e10. [PMID: 28772123 DOI: 10.1016/j.neuron.2017.07.004] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 05/08/2017] [Accepted: 07/06/2017] [Indexed: 11/18/2022]
Abstract
Munc13 catalyzes the transit of syntaxin from a closed complex with Munc18 into the ternary SNARE complex. Here we report a new function of Munc13, independent of Munc18: it promotes the proper syntaxin/synaptobrevin subconfiguration during assembly of the ternary SNARE complex. In cooperation with Munc18, Munc13 additionally ensures the proper syntaxin/SNAP-25 subconfiguration. In a reconstituted fusion assay with SNAREs, complexin, and synaptotagmin, inclusion of both Munc13 and Munc18 quadruples the Ca2+-triggered amplitude and achieves Ca2+ sensitivity at near-physiological concentrations. In Munc13-1/2 double-knockout neurons, expression of a constitutively open mutant of syntaxin could only minimally restore neurotransmitter release relative to Munc13-1 rescue. Together, the physiological functions of Munc13 may be related to regulation of proper SNARE complex assembly.
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Affiliation(s)
- Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Hong Jun Rhee
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
| | - Choongku Lee
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
| | - Bekir Altas
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
| | - Minglei Zhao
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Richard A Pfuetzner
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Austin L Wang
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
| | - JeongSeop Rhee
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
| | - Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305, USA; Department of Structural Biology, Stanford University, Stanford, CA 94305, USA; Department of Photon Science, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA.
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167
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Guan Z, Bykhovskaia M, Jorquera RA, Sutton RB, Akbergenova Y, Littleton JT. A synaptotagmin suppressor screen indicates SNARE binding controls the timing and Ca 2+ cooperativity of vesicle fusion. eLife 2017; 6:28409. [PMID: 28895532 PMCID: PMC5617632 DOI: 10.7554/elife.28409] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 09/11/2017] [Indexed: 01/05/2023] Open
Abstract
The synaptic vesicle Ca2+ sensor Synaptotagmin binds Ca2+ through its two C2 domains to trigger membrane interactions. Beyond membrane insertion by the C2 domains, other requirements for Synaptotagmin activity are still being elucidated. To identify key residues within Synaptotagmin required for vesicle cycling, we took advantage of observations that mutations in the C2B domain Ca2+-binding pocket dominantly disrupt release from invertebrates to humans. We performed an intragenic screen for suppressors of lethality induced by expression of Synaptotagmin C2B Ca2+-binding mutants in Drosophila. This screen uncovered essential residues within Synaptotagmin that suggest a structural basis for several activities required for fusion, including a C2B surface implicated in SNARE complex interaction that is required for rapid synchronization and Ca2+ cooperativity of vesicle release. Using electrophysiological, morphological and computational characterization of these mutants, we propose a sequence of molecular interactions mediated by Synaptotagmin that promote Ca2+ activation of the synaptic vesicle fusion machinery.
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Affiliation(s)
- Zhuo Guan
- Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Maria Bykhovskaia
- Department of Neurology, School of Medicine, Wayne State University, Detroit, United States
| | - Ramon A Jorquera
- Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico
| | - Roger Bryan Sutton
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, United States
| | - Yulia Akbergenova
- Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - J Troy Littleton
- Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
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168
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Liu X, Seven AB, Xu J, Esser V, Su L, Ma C, Rizo J. Simultaneous lipid and content mixing assays for in vitro reconstitution studies of synaptic vesicle fusion. Nat Protoc 2017; 12:2014-2028. [PMID: 28858288 PMCID: PMC6163043 DOI: 10.1038/nprot.2017.068] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
This protocol describes reconstitution assays to study how the neurotransmitter release machinery triggers Ca2+-dependent synaptic vesicle fusion. The assays monitor fusion between proteoliposomes containing the synaptic vesicle SNARE synaptobrevin (with or without the Ca2+ sensor synaptotagmin-1) and proteoliposomes initially containing the plasma membrane SNAREs syntaxin-1 and soluble NSF attachment protein (SNAP)-25. Lipid mixing (from fluorescence de-quenching of Marina-Blue-labeled lipids) and content mixing (from development of fluorescence resonance energy transfer (FRET) between phycoerythrin-biotin (PhycoE-Biotin) and Cy5-streptavidin trapped in the two proteoliposome populations) are measured simultaneously to ensure that true, nonleaky membrane fusion is monitored. This protocol is based on a method developed to study yeast vacuolar fusion. In contrast to other protocols used to study the release machinery, this assay incorporates N-ethylmaleimide sensitive factor (NSF) and α-SNAP, which disassemble syntaxin-1 and SNAP-25 heterodimers. As a result, fusion requires Munc18-1, which binds to the released syntaxin-1, and Munc13-1, which, together with Munc18-1, orchestrates SNARE complex assembly. The protocol can be readily adapted to investigation of other types of intracellular membrane fusion by using appropriate alternative proteins. Total time required for one round of the assay is 4 d.
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Affiliation(s)
- Xiaoxia Liu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Alpay Burak Seven
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Victoria Esser
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Lijing Su
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - 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
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
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169
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Reddy-Alla S, Böhme MA, Reynolds E, Beis C, Grasskamp AT, Mampell MM, Maglione M, Jusyte M, Rey U, Babikir H, McCarthy AW, Quentin C, Matkovic T, Bergeron DD, Mushtaq Z, Göttfert F, Owald D, Mielke T, Hell SW, Sigrist SJ, Walter AM. Stable Positioning of Unc13 Restricts Synaptic Vesicle Fusion to Defined Release Sites to Promote Synchronous Neurotransmission. Neuron 2017; 95:1350-1364.e12. [DOI: 10.1016/j.neuron.2017.08.016] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 05/10/2017] [Accepted: 08/09/2017] [Indexed: 12/24/2022]
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170
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Yamamoto M, Hirata K, Yamashita K, Hasegawa K, Ueno G, Ago H, Kumasaka T. Protein microcrystallography using synchrotron radiation. IUCRJ 2017; 4:529-539. [PMID: 28989710 PMCID: PMC5619846 DOI: 10.1107/s2052252517008193] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Accepted: 06/02/2017] [Indexed: 05/21/2023]
Abstract
The progress in X-ray microbeam applications using synchrotron radiation is beneficial to structure determination from macromolecular microcrystals such as small in meso crystals. However, the high intensity of microbeams causes severe radiation damage, which worsens both the statistical quality of diffraction data and their resolution, and in the worst cases results in the failure of structure determination. Even in the event of successful structure determination, site-specific damage can lead to the misinterpretation of structural features. In order to overcome this issue, technological developments in sample handling and delivery, data-collection strategy and data processing have been made. For a few crystals with dimensions of the order of 10 µm, an elegant two-step scanning strategy works well. For smaller samples, the development of a novel method to analyze multiple isomorphous microcrystals was motivated by the success of serial femtosecond crystallography with X-ray free-electron lasers. This method overcame the radiation-dose limit in diffraction data collection by using a sufficient number of crystals. Here, important technologies and the future prospects for microcrystallography are discussed.
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Affiliation(s)
- Masaki Yamamoto
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Kunio Hirata
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Keitaro Yamashita
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Kazuya Hasegawa
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Go Ueno
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Hideo Ago
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Takashi Kumasaka
- Advanced Photon Technology Division, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
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171
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How does the stimulus define exocytosis in adrenal chromaffin cells? Pflugers Arch 2017; 470:155-167. [DOI: 10.1007/s00424-017-2052-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 07/28/2017] [Accepted: 08/01/2017] [Indexed: 12/28/2022]
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172
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Wang J, Li F, Bello OD, Sindelar CV, Pincet F, Krishnakumar SS, Rothman JE. Circular oligomerization is an intrinsic property of synaptotagmin. eLife 2017; 6. [PMID: 28850328 PMCID: PMC5576491 DOI: 10.7554/elife.27441] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Accepted: 08/11/2017] [Indexed: 11/13/2022] Open
Abstract
Previously, we showed that synaptotagmin1 (Syt1) forms Ca2+-sensitive ring-like oligomers on membranes containing acidic lipids and proposed a potential role in regulating neurotransmitter release (Zanetti et al., 2016). Here, we report that Syt1 assembles into similar ring-like oligomers in solution when triggered by naturally occurring polyphosphates (PIP2 and ATP) and magnesium ions (Mg2+). These soluble Syt1 rings were observed by electron microscopy and independently demonstrated and quantified using fluorescence correlation spectroscopy. Oligomerization is triggered when polyphosphates bind to the polylysine patch in C2B domain and is stabilized by Mg2+, which neutralizes the Ca2+-binding aspartic acids that likely contribute to the C2B interface in the oligomer. Overall, our data show that ring-like polymerization is an intrinsic property of Syt1 with reasonable affinity that can be triggered by the vesicle docking C2B-PIP2 interaction and raise the possibility that Syt1 rings could pre-form on the synaptic vesicle to facilitate docking.
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Affiliation(s)
- Jing Wang
- Departments of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Feng Li
- Departments of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Oscar D Bello
- Departments of Cell Biology, Yale University School of Medicine, New Haven, United States.,Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, United Kingdom
| | - Charles Vaughn Sindelar
- Departments of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, United States
| | - Frédéric Pincet
- Departments of Cell Biology, Yale University School of Medicine, New Haven, United States.,Laboratoire de Physique Statistique, UMR CNRS 8550 Associée aux Universités Paris 6 et Paris 7, Paris, France
| | - Shyam S Krishnakumar
- Departments of Cell Biology, Yale University School of Medicine, New Haven, United States.,Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, United Kingdom
| | - James E Rothman
- Departments of Cell Biology, Yale University School of Medicine, New Haven, United States.,Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, United Kingdom
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173
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Gipson P, Fukuda Y, Danev R, Lai Y, Chen DH, Baumeister W, Brunger AT. Morphologies of synaptic protein membrane fusion interfaces. Proc Natl Acad Sci U S A 2017; 114:9110-9115. [PMID: 28739947 PMCID: PMC5576828 DOI: 10.1073/pnas.1708492114] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurotransmitter release is orchestrated by synaptic proteins, such as SNAREs, synaptotagmin, and complexin, but the molecular mechanisms remain unclear. We visualized functionally active synaptic proteins reconstituted into proteoliposomes and their interactions in a native membrane environment by electron cryotomography with a Volta phase plate for improved resolvability. The images revealed individual synaptic proteins and synaptic protein complex densities at prefusion contact sites between membranes. We observed distinct morphologies of individual synaptic proteins and their complexes. The minimal system, consisting of neuronal SNAREs and synaptotagmin-1, produced point and long-contact prefusion states. Morphologies and populations of these states changed as the regulatory factors complexin and Munc13 were added. Complexin increased the membrane separation, along with a higher propensity of point contacts. Further inclusion of the priming factor Munc13 exclusively restricted prefusion states to point contacts, all of which efficiently fused upon Ca2+ triggering. We conclude that synaptic proteins have evolved to limit possible contact site assemblies and morphologies to those that promote fast Ca2+-triggered release.
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Affiliation(s)
- Preeti Gipson
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Department of Photon Science, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
| | - Yoshiyuki Fukuda
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Radostin Danev
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Department of Photon Science, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
| | - Dong-Hua Chen
- Department of Structural Biology, Stanford University, Stanford, CA 94305
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305;
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Department of Photon Science, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
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174
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Interactions Between SNAP-25 and Synaptotagmin-1 Are Involved in Vesicle Priming, Clamping Spontaneous and Stimulating Evoked Neurotransmission. J Neurosci 2017; 36:11865-11880. [PMID: 27881774 DOI: 10.1523/jneurosci.1011-16.2016] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2016] [Revised: 09/29/2016] [Accepted: 09/29/2016] [Indexed: 01/20/2023] Open
Abstract
Whether interactions between synaptotagmin-1 (syt-1) and the soluble NSF attachment protein receptors (SNAREs) are required during neurotransmission is debated. We examined five SNAP-25 mutations designed to interfere with syt-1 interactions. One mutation, D51/E52/E55A, targeted negative charges within region II of the primary interface (Zhou et al., 2015); two mutations targeted region I (D166A and D166/E170A) and one mutation targeted both (D51/E52/E55/D166A). The final mutation (D186/D193A) targeted C-terminal residues not expected to interact with syt-1. An in vitro assay showed that the region I, region II, and region I+II (D51/E52/E55/D166A) mutants markedly reduced the attachment between syt-1 and t-SNARE-carrying vesicles in the absence of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. In the presence of PI(4,5)P2, vesicle attachment was unaffected by mutation. When expressed in Snap-25-null mouse autaptic neurons, region I mutations reduced the size of the readily releasable pool of vesicles, whereas the region II mutation reduced vesicular release probability. Combining both in the D51/E52/E55/D166A mutation abrogated evoked release. These data point to a division of labor between region I (vesicle priming) and region II (evoked release). Spontaneous release was disinhibited by region I mutations and found to correlate with defective complexin (Cpx) clamping in an in vitro fusion assay, pointing to an interdependent role of synaptotagmin and Cpx in release clamping. Mutation in region II (D51/E52/E55A) also unclamped release, but this effect could be overcome by synaptotagmin overexpression, arguing against an obligatory role in clamping. We conclude that three synaptic release functions of syt-1, vesicle priming, spontaneous release clamping, and evoked release triggering, depend on direct SNARE complex interaction. SIGNIFICANCE STATEMENT The function of synaptotagmin-1 (syt-1):soluble NSF attachment protein receptor (SNARE) interactions during neurotransmission remains unclear. We mutated SNAP-25 within the recently identified region I and region II of the primary synaptotagmin:SNARE interface. Using in vitro assays and rescue experiments in autaptic neurons, we show that interactions within region II of the primary interface are necessary for synchronized calcium-triggered release, whereas region I is involved in vesicle priming. Spontaneous release was disinhibited by region I mutation and found to correlate with defective complexin (Cpx) clamping in vitro, pointing to an interdependent role of synaptotagmin and Cpx in release clamping. Therefore, vesicle priming, clamping spontaneous release, and eliciting evoked release are three different functions of syt-1 that involve different interaction modes with the SNARE complex.
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175
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The primed SNARE-complexin-synaptotagmin complex for neuronal exocytosis. Nature 2017; 548:420-425. [PMID: 28813412 DOI: 10.1038/nature23484] [Citation(s) in RCA: 181] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 07/14/2017] [Indexed: 12/17/2022]
Abstract
Synaptotagmin, complexin, and neuronal SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins mediate evoked synchronous neurotransmitter release, but the molecular mechanisms mediating the cooperation between these molecules remain unclear. Here we determine crystal structures of the primed pre-fusion SNARE-complexin-synaptotagmin-1 complex. These structures reveal an unexpected tripartite interface between synaptotagmin-1 and both the SNARE complex and complexin. Simultaneously, a second synaptotagmin-1 molecule interacts with the other side of the SNARE complex via the previously identified primary interface. Mutations that disrupt either interface in solution also severely impair evoked synchronous release in neurons, suggesting that both interfaces are essential for the primed pre-fusion state. Ca2+ binding to the synaptotagmin-1 molecules unlocks the complex, allows full zippering of the SNARE complex, and triggers membrane fusion. The tripartite SNARE-complexin-synaptotagmin-1 complex at a synaptic vesicle docking site has to be unlocked for triggered fusion to start, explaining the cooperation between complexin and synaptotagmin-1 in synchronizing evoked release on the sub-millisecond timescale.
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176
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Li Y, Wang S, Li T, Zhu L, Xu Y, Ma C. A Stimulation Function of Synaptotagmin-1 in Ternary SNARE Complex Formation Dependent on Munc18 and Munc13. Front Mol Neurosci 2017; 10:256. [PMID: 28860966 PMCID: PMC5559510 DOI: 10.3389/fnmol.2017.00256] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2017] [Accepted: 07/28/2017] [Indexed: 12/12/2022] Open
Abstract
The Ca2+ sensor synaptotagmin-1 (Syt1) plays an essential function in synaptic exocytosis. Recently, Syt1 has been implicated in synaptic vesicle priming, a maturation step prior to Ca2+-triggered membrane fusion that is believed to involve formation of the ternary SNARE complex and require priming proteins Munc18-1 and Munc13-1. However, the mechanisms of Syt1 in synaptic vesicle priming are still unclear. In this study, we found that Syt1 stimulates the transition from the Munc18-1/syntaxin-1 complex to the ternary SNARE complex catalyzed by Munc13-1. This stimulation can be further enhanced in a membrane-containing environment. Further, we showed that Syt1, together with Munc18-1 and Munc13-1, stimulates trans ternary SNARE complex formation on membranes in a manner resistant to disassembly factors NSF and α-SNAP. Disruption of a proposed Syt1/SNARE binding interface strongly abrogated the stimulation function of Syt1. Our results suggest that binding of Syt1 to an intermediate SNARE assembly with Munc18-1 and Munc13-1 is critical for the stimulation function of Syt1 in ternary SNARE complex formation, and this stimulation may underlie the priming function of Syt1 in synaptic exocytosis.
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Affiliation(s)
- Yun Li
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Tianzhi Li
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Le Zhu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Yuanyuan Xu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
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177
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Jackman SL, Regehr WG. The Mechanisms and Functions of Synaptic Facilitation. Neuron 2017; 94:447-464. [PMID: 28472650 DOI: 10.1016/j.neuron.2017.02.047] [Citation(s) in RCA: 224] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 02/23/2017] [Accepted: 02/28/2017] [Indexed: 12/22/2022]
Abstract
The ability of the brain to store and process information relies on changing the strength of connections between neurons. Synaptic facilitation is a form of short-term plasticity that enhances synaptic transmission for less than a second. Facilitation is a ubiquitous phenomenon thought to play critical roles in information transfer and neural processing. Yet our understanding of the function of facilitation remains largely theoretical. Here we review proposed roles for facilitation and discuss how recent progress in uncovering the underlying molecular mechanisms could enable experiments that elucidate how facilitation, and short-term plasticity in general, contributes to circuit function and animal behavior.
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Affiliation(s)
- Skyler L Jackman
- Department of Neurobiology, Harvard Medical School, Boston, MA 02118, USA
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, Boston, MA 02118, USA.
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178
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Dynamic Partitioning of Synaptic Vesicle Pools by the SNARE-Binding Protein Tomosyn. J Neurosci 2017; 36:11208-11222. [PMID: 27807164 DOI: 10.1523/jneurosci.1297-16.2016] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 09/13/2016] [Indexed: 12/13/2022] Open
Abstract
Neural networks engaged in high-frequency activity rely on sustained synaptic vesicle recycling and coordinated recruitment from functionally distinct synaptic vesicle (SV) pools. However, the molecular pathways matching neural activity to SV dynamics and release requirements remain unclear. Here we identify unique roles of SNARE-binding Tomosyn1 (Tomo1) proteins as activity-dependent substrates that regulate dynamics of SV pool partitioning at rat hippocampal synapses. Our analysis is based on monitoring changes in distinct functionally defined SV pools via V-Glut1-pHluorin fluorescence in cultured hippocampal neurons in response to alterations in presynaptic protein expression. Specifically, we find knockdown of Tomo1 facilitates release efficacy from the Readily Releasable Pool (RRP), and regulates SV distribution to the Total Recycling Pool (TRP), which is matched by a decrease in the SV Resting Pool. Notably, these effects were reversed by Tomo1 rescue and overexpression. Further, we identify that these actions of Tomo1 are regulated via activity-dependent phosphorylation by cyclin-dependent kinase 5 (Cdk5). Assessment of molecular interactions that may contribute to these actions identified Tomo1 interaction with the GTP-bound state of Rab3A, an SV GTPase involved in SV targeting and presynaptic membrane tethering. In addition, Tomo1 via Rab3A-GTP was also observed to interact with Synapsin 1a/b cytoskeletal interacting proteins. Finally, our data indicate that Tomo1 regulation of SV pool sizes serves to adapt presynaptic neurotransmitter release to chronic silencing of network activity. Overall, the results establish Tomo1 proteins as central mediators in neural activity-dependent changes in SV distribution among SV pools. SIGNIFICANCE STATEMENT Although information transfer at central synapses via sustained high-frequency neural activity requires coordinated synaptic vesicle (SV) recycling, the mechanism(s) by which synapses sense and dynamically modify SV pools to match network demands remains poorly defined. To advance understanding, we quantified SV pool sizes and their sensitivity to neural activity while altering Tomo1 expression, a putative regulator of the presynaptic Readily Releasable Pool. Remarkably, we find Tomo1 actions to extend beyond the Readily Releasable Pool to mediate the Total Recycling Pool and SV Resting Pool distribution, and this action is sensitive to neural activity through Cdk5 phosphorylation of Tomo1. Moreover, Tomo1 appears to exert these actions through interaction with Rab3A-GTP and synapsin proteins. Together, our results argue that Tomo1 is a central mediator of SV availability for neurotransmission.
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179
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Wang F, Wu Z, Zha X, Cai Y, Wu B, Jia X, Zhu D. Concurrent administration of thyroxine and donepezil induces plastic changes in the prefrontal cortex of adult hypothyroid rats. Mol Med Rep 2017; 16:3233-3241. [PMID: 28713915 PMCID: PMC5548062 DOI: 10.3892/mmr.2017.6977] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Accepted: 04/19/2017] [Indexed: 01/22/2023] Open
Abstract
The aim of the present study was to observe the effects of the concurrent administration of thyroxine (T4) and an acetylcholinesterase (AChE) inhibitor, donepezil (DON), on the hypothyroidism-induced ultrastructural changes of the prefrontal cortex (PFC) in adult rats. The acetylcholine (ACh) content and AChE activity was assessed, as well as the expressions of synaptotagmin-1 (syt-1) and SNAP-25 were analyzed in the rats. Adding 0.05% propylthiouracil to rats' drinking water induced a hypothyroid rat model. The animals were treated with T4 and DON administered separately or in combination from the fifth week. Transmission electron microscope analysis revealed that hypothyroidism induced marked ultrastructural changes, including the neurons, the synapses and the myelin sheath in the PFC. T4 or DON treatment improved the morphologic features of the PFC, and the performance of the T4 combined DON group was the closest to the control group. Moreover, hypothyroidism significantly decreased the content of ACh (29.8%) and activity of AChE (27.8%), which were restored to control values by T4 administration. In addition, DON treatment restored ACh content to normal. At the protein level, hypothyroidism increased the levels of syt-1 and SNAP-25 in the PFC, both of which were not restored to control values following T4 administration, while concurrent administration of T4 and DON was able to induce this effect. These results suggested that adult-onset hypothyroidism induce morphological, biochemical and molecular alterations in the PFC, combined administration of T4 and DON induce plastic changes in the PFC, different from that of the standard T4 therapy, and that the DON treatment may facilitate the recovery of synaptic protein impairments induced by hypothyroidism.
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Affiliation(s)
- Fen Wang
- Department of Endocrinology, Anhui Geriatric Institute, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
| | - Zhangbi Wu
- Department of Endocrinology, Anhui Geriatric Institute, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
| | - Xiaoxue Zha
- Department of Endocrinology, Anhui Geriatric Institute, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
| | - Yaojun Cai
- Department of Endocrinology, Anhui Geriatric Institute, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
| | - Bo Wu
- Department of Endocrinology, Anhui Geriatric Institute, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
| | - Xuemei Jia
- Comprehensive Laboratory, College of Basic Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China
| | - Defa Zhu
- Department of Endocrinology, Anhui Geriatric Institute, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230022, P.R. China
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Ferrer-Orta C, Pérez-Sánchez MD, Coronado-Parra T, Silva C, López-Martínez D, Baltanás-Copado J, Gómez-Fernández JC, Corbalán-García S, Verdaguer N. Structural characterization of the Rabphilin-3A-SNAP25 interaction. Proc Natl Acad Sci U S A 2017; 114:E5343-E5351. [PMID: 28634303 PMCID: PMC5502619 DOI: 10.1073/pnas.1702542114] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membrane fusion is essential in a myriad of eukaryotic cell biological processes, including the synaptic transmission. Rabphilin-3A is a membrane trafficking protein involved in the calcium-dependent regulation of secretory vesicle exocytosis in neurons and neuroendocrine cells, but the underlying mechanism remains poorly understood. Here, we report the crystal structures and biochemical analyses of Rabphilin-3A C2B-SNAP25 and C2B-phosphatidylinositol 4,5-bisphosphate (PIP2) complexes, revealing how Rabphilin-3A C2 domains operate in cooperation with PIP2/Ca2+ and SNAP25 to bind the plasma membrane, adopting a conformation compatible to interact with the complete SNARE complex. Comparisons with the synaptotagmin1-SNARE show that both proteins contact the same SNAP25 surface, but Rabphilin-3A uses a unique structural element. Data obtained here suggest a model to explain the Ca2+-dependent fusion process by membrane bending with a myriad of variations depending on the properties of the C2 domain-bearing protein, shedding light to understand the fine-tuning control of the different vesicle fusion events.
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Affiliation(s)
- Cristina Ferrer-Orta
- Structural Biology Unit, Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Cientificas, 08028 Barcelona, Spain;
| | - María Dolores Pérez-Sánchez
- Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, Instituto Murciano de Investigación Biosanitaria Virgen de la Arrixaca, 30100 Murcia, Spain
| | - Teresa Coronado-Parra
- Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, Instituto Murciano de Investigación Biosanitaria Virgen de la Arrixaca, 30100 Murcia, Spain
| | - Cristina Silva
- Structural Biology Unit, Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Cientificas, 08028 Barcelona, Spain
| | - David López-Martínez
- Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, Instituto Murciano de Investigación Biosanitaria Virgen de la Arrixaca, 30100 Murcia, Spain
| | - Jesús Baltanás-Copado
- Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, Instituto Murciano de Investigación Biosanitaria Virgen de la Arrixaca, 30100 Murcia, Spain
| | - Juan Carmelo Gómez-Fernández
- Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, Instituto Murciano de Investigación Biosanitaria Virgen de la Arrixaca, 30100 Murcia, Spain
| | - Senena Corbalán-García
- Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, Instituto Murciano de Investigación Biosanitaria Virgen de la Arrixaca, 30100 Murcia, Spain
| | - Núria Verdaguer
- Structural Biology Unit, Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Cientificas, 08028 Barcelona, Spain;
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181
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Molecular regulation of insulin granule biogenesis and exocytosis. Biochem J 2017; 473:2737-56. [PMID: 27621482 DOI: 10.1042/bcj20160291] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 04/19/2016] [Indexed: 12/15/2022]
Abstract
Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by hyperglycemia, insulin resistance and hyperinsulinemia in early disease stages but a relative insulin insufficiency in later stages. Insulin, a peptide hormone, is produced in and secreted from pancreatic β-cells following elevated blood glucose levels. Upon its release, insulin induces the removal of excessive exogenous glucose from the bloodstream primarily by stimulating glucose uptake into insulin-dependent tissues as well as promoting hepatic glycogenesis. Given the increasing prevalence of T2DM worldwide, elucidating the underlying mechanisms and identifying the various players involved in the synthesis and exocytosis of insulin from β-cells is of utmost importance. This review summarizes our current understanding of the route insulin takes through the cell after its synthesis in the endoplasmic reticulum as well as our knowledge of the highly elaborate network that controls insulin release from the β-cell. This network harbors potential targets for anti-diabetic drugs and is regulated by signaling cascades from several endocrine systems.
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182
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Katti S, Nyenhuis SB, Her B, Srivastava AK, Taylor AB, Hart PJ, Cafiso DS, Igumenova TI. Non-Native Metal Ion Reveals the Role of Electrostatics in Synaptotagmin 1-Membrane Interactions. Biochemistry 2017; 56:3283-3295. [PMID: 28574251 DOI: 10.1021/acs.biochem.7b00188] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
C2 domains are independently folded modules that often target their host proteins to anionic membranes in a Ca2+-dependent manner. In these cases, membrane association is triggered by Ca2+ binding to the negatively charged loop region of the C2 domain. Here, we used a non-native metal ion, Cd2+, in lieu of Ca2+ to gain insight into the contributions made by long-range Coulombic interactions and direct metal ion-lipid bridging to membrane binding. Using X-ray crystallography, NMR, Förster resonance energy transfer, and vesicle cosedimentation assays, we demonstrate that, although Cd2+ binds to the loop region of C2A/B domains of synaptotagmin 1 with high affinity, long-range Coulombic interactions are too weak to support membrane binding of individual domains. We attribute this behavior to two factors: the stoichiometry of Cd2+ binding to the loop regions of the C2A and C2B domains and the impaired ability of Cd2+ to directly coordinate the lipids. In contrast, electron paramagnetic resonance experiments revealed that Cd2+ does support membrane binding of the C2 domains in full-length synaptotagmin 1, where the high local lipid concentrations that result from membrane tethering can partially compensate for lack of a full complement of divalent metal ions and specific lipid coordination in Cd2+-complexed C2A/B domains. Our data suggest that long-range Coulombic interactions alone can drive the initial association of C2A/B with anionic membranes and that Ca2+ further augments membrane binding by the formation of metal ion-lipid coordination bonds and additional Ca2+ ion binding to the C2 domain loop regions.
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Affiliation(s)
- Sachin Katti
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Sarah B Nyenhuis
- Department of Chemistry and Biophysics Program, University of Virginia , Charlottesville, Virginia 22904, United States
| | - Bin Her
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Atul K Srivastava
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Alexander B Taylor
- Department of Biochemistry and Structural Biology and the X-ray Crystallography Core Laboratory, University of Texas Health Science Center at San Antonio , San Antonio, Texas 78229, United States
| | - P John Hart
- Department of Biochemistry and Structural Biology and the X-ray Crystallography Core Laboratory, University of Texas Health Science Center at San Antonio , San Antonio, Texas 78229, United States
| | - David S Cafiso
- Department of Chemistry and Biophysics Program, University of Virginia , Charlottesville, Virginia 22904, United States
| | - Tatyana I Igumenova
- Department of Biochemistry and Biophysics, Texas A&M University , 300 Olsen Boulevard, College Station, Texas 77843, United States
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183
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Zurawski Z, Page B, Chicka MC, Brindley RL, Wells CA, Preininger AM, Hyde K, Gilbert JA, Cruz-Rodriguez O, Currie KPM, Chapman ER, Alford S, Hamm HE. Gβγ directly modulates vesicle fusion by competing with synaptotagmin for binding to neuronal SNARE proteins embedded in membranes. J Biol Chem 2017; 292:12165-12177. [PMID: 28515322 DOI: 10.1074/jbc.m116.773523] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Revised: 05/10/2017] [Indexed: 01/11/2023] Open
Abstract
Gi/o-coupled G protein-coupled receptors can inhibit neurotransmitter release at synapses via multiple mechanisms. In addition to Gβγ-mediated modulation of voltage-gated calcium channels (VGCC), inhibition can also be mediated through the direct interaction of Gβγ subunits with the soluble N-ethylmaleimide attachment protein receptor (SNARE) complex of the vesicle fusion apparatus. Binding studies with soluble SNARE complexes have shown that Gβγ binds to both ternary SNARE complexes, t-SNARE heterodimers, and monomeric SNAREs, competing with synaptotagmin 1(syt1) for binding sites on t-SNARE. However, in secretory cells, Gβγ, SNAREs, and synaptotagmin interact in the lipid environment of a vesicle at the plasma membrane. To approximate this environment, we show that fluorescently labeled Gβγ interacts specifically with lipid-embedded t-SNAREs consisting of full-length syntaxin 1 and SNAP-25B at the membrane, as measured by fluorescence polarization. Fluorescently labeled syt1 undergoes competition with Gβγ for SNARE-binding sites in lipid environments. Mutant Gβγ subunits that were previously shown to be more efficacious at inhibiting Ca2+-triggered exocytotic release than wild-type Gβγ were also shown to bind SNAREs at a higher affinity than wild type in a lipid environment. These mutant Gβγ subunits were unable to inhibit VGCC currents. Specific peptides corresponding to regions on Gβ and Gγ shown to be important for the interaction disrupt the interaction in a concentration-dependent manner. In in vitro fusion assays using full-length t- and v-SNAREs embedded in liposomes, Gβγ inhibited Ca2+/synaptotagmin-dependent fusion. Together, these studies demonstrate the importance of these regions for the Gβγ-SNARE interaction and show that the target of Gβγ, downstream of VGCC, is the membrane-embedded SNARE complex.
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Affiliation(s)
- Zack Zurawski
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600
| | - Brian Page
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612-7308
| | - Michael C Chicka
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, 53705
| | - Rebecca L Brindley
- Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600
| | - Christopher A Wells
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600
| | - Anita M Preininger
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600
| | - Karren Hyde
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600
| | - James A Gilbert
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600
| | - Osvaldo Cruz-Rodriguez
- Departments of Pharmacology and Biological Chemistry, Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
| | - Kevin P M Currie
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600; Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600
| | - Edwin R Chapman
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, 53705
| | - Simon Alford
- Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612-7308
| | - Heidi E Hamm
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600.
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184
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Shi Y, Zhang Y, Lou J. The influence of cell membrane and SNAP25 linker loop on the dynamics and unzipping of SNARE complex. PLoS One 2017; 12:e0176235. [PMID: 28426820 PMCID: PMC5398687 DOI: 10.1371/journal.pone.0176235] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 04/08/2017] [Indexed: 11/29/2022] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is composed of three neuronal proteins VAMP2, Syntaxin and SNAP25, which plays a core role during the process of membrane fusion. The zipping assembly of the SNARE complex releases energies and drives the vesicle and cell membrane into close proximity. In this study, we use all-atom molecular dynamics simulations to probe the dynamics of SNARE and its unzipping process in the context of membrane at the atomistic details. Our results indicated that the NTD of SNARE core domain is relatively more stable than CTD, which is in agreement with previous experiments. More importantly, possible interactions between the linker loop (LL) region of SNAP25 and VAMP2 are observed, suggests that the LL region may facilitate VAMP2 binding and SNARE initiation. The forced unzipping of SNARE in the presence of membrane and LL of SNAP25 reveals the possible pathway for energy generation of SNARE zipping, provides information to understand how force may regulate the cooperativity between the membrane and the SNARE complex.
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Affiliation(s)
- Yi Shi
- School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, China
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Yong Zhang
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Jizhong Lou
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- * E-mail:
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185
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Sugahara M, Nakane T, Masuda T, Suzuki M, Inoue S, Song C, Tanaka R, Nakatsu T, Mizohata E, Yumoto F, Tono K, Joti Y, Kameshima T, Hatsui T, Yabashi M, Nureki O, Numata K, Nango E, Iwata S. Hydroxyethyl cellulose matrix applied to serial crystallography. Sci Rep 2017; 7:703. [PMID: 28386083 PMCID: PMC5429652 DOI: 10.1038/s41598-017-00761-0] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 03/13/2017] [Indexed: 11/24/2022] Open
Abstract
Serial femtosecond crystallography (SFX) allows structures of proteins to be determined at room temperature with minimal radiation damage. A highly viscous matrix acts as a crystal carrier for serial sample loading at a low flow rate that enables the determination of the structure, while requiring consumption of less than 1 mg of the sample. However, a reliable and versatile carrier matrix for a wide variety of protein samples is still elusive. Here we introduce a hydroxyethyl cellulose-matrix carrier, to determine the structure of three proteins. The de novo structure determination of proteinase K from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of the praseodymium atom was demonstrated using 3,000 diffraction images.
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Affiliation(s)
- Michihiro Sugahara
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.
| | - Takanori Nakane
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Tetsuya Masuda
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.,Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
| | - Mamoru Suzuki
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.,Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Shigeyuki Inoue
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.,Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Changyong Song
- Department of Physics, POSTECH, Pohang, 37673, Republic of Korea
| | - Rie Tanaka
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan
| | - Toru Nakatsu
- Department of Structural Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida Shimoadachi-cho, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Eiichi Mizohata
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Fumiaki Yumoto
- Structural Biology Research Center, KEK High Energy Accelerator Research Organization, Tsukuba, Ibaraki, 305-0801, Japan
| | - Kensuke Tono
- Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan
| | - Yasumasa Joti
- Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan
| | - Takashi Kameshima
- Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan
| | - Takaki Hatsui
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan
| | - Makina Yabashi
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan
| | - Osamu Nureki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Keiji Numata
- Enzyme Research Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science, Hirosawa, Wako-shi, Saitama, 351-0198, Japan
| | - Eriko Nango
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan
| | - So Iwata
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.,Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
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186
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Synaptotagmin2 (Syt2) Drives Fast Release Redundantly with Syt1 at the Output Synapses of Parvalbumin-Expressing Inhibitory Neurons. J Neurosci 2017; 37:4604-4617. [PMID: 28363983 DOI: 10.1523/jneurosci.3736-16.2017] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 03/22/2017] [Accepted: 03/27/2017] [Indexed: 12/16/2022] Open
Abstract
Parvalbumin-expressing inhibitory neurons in the mammalian CNS are specialized for fast transmitter release at their output synapses. However, the Ca2+ sensor(s) used by identified inhibitory synapses, including the output synapses of parvalbumin-expressing inhibitory neurons, have only recently started to be addressed. Here, we investigated the roles of Syt1 and Syt2 at two types of fast-releasing inhibitory connections in the mammalian CNS: the medial nucleus of the trapezoid body to lateral superior olive glycinergic synapse, and the basket/stellate cell-Purkinje GABAergic synapse in the cerebellum. We used conditional and conventional knock-out (KO) mouse lines, with viral expression of Cre-recombinase and a light-activated ion channel for optical stimulation of the transduced fibers, to produce Syt1-Syt2 double KO synapses in vivo Surprisingly, we found that KO of Syt2 alone had only minor effects on evoked transmitter release, despite the clear presence of the protein in inhibitory nerve terminals revealed by immunohistochemistry. We show that Syt1 is weakly coexpressed at these inhibitory synapses and must be genetically inactivated together with Syt2 to achieve a significant reduction and desynchronization of fast release. Thus, our work identifies the functionally relevant Ca2+ sensor(s) at fast-releasing inhibitory synapses and shows that two major Syt isoforms can cooperate to mediate release at a given synaptic connection.SIGNIFICANCE STATEMENT During synaptic transmission, the influx of Ca2+ into the presynaptic nerve terminal activates a Ca2+ sensor for vesicle fusion, a crucial step in the activity-dependent release of neurotransmitter. Synaptotagmin (Syt) proteins, and especially Syt1 and Syt2, have been identified as the Ca2+ sensor at excitatory synapses, but the Ca2+ sensor(s) at inhibitory synapses in native brain tissue are not well known. We found that both Syt1 and Syt2 need to be genetically inactivated to cause a significant reduction of activity-evoked release at two types of fast inhibitory synapses in mouse brain. Thus, we identify Syt2 as a functionally important Ca2+ sensor at fast-releasing inhibitory synapses, and show that Syt1 and Syt2 can redundantly control transmitter release at specific brain synapses.
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187
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Wu D, Bacaj T, Morishita W, Goswami D, Arendt KL, Xu W, Chen L, Malenka RC, Südhof TC. Postsynaptic synaptotagmins mediate AMPA receptor exocytosis during LTP. Nature 2017; 544:316-321. [PMID: 28355182 PMCID: PMC5734942 DOI: 10.1038/nature21720] [Citation(s) in RCA: 131] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 02/22/2017] [Indexed: 12/19/2022]
Abstract
Strengthening of synaptic connections by NMDA-receptor-dependent long-term potentiation (LTP) shapes neural circuits and mediates learning and memory. During NMDA-receptor-dependent LTP induction, Ca2+-influx stimulates recruitment of synaptic AMPA-receptors, thereby strengthening synapses. How Ca2+ induces AMPA-receptor recruitment, however, remains unclear. Here we show that, in pyramidal neurons of the hippocampal CA1-region, blocking postsynaptic expression of both synaptotagmin-1 and synaptotagmin-7, but not of synaptotagmin-1 or synaptotagmin-7 alone, abolished LTP. LTP was rescued by wild-type but not by Ca2+-binding-deficient mutant synaptotagmin-7. Blocking postsynaptic synaptotagmin-1/7 expression did not impair basal synaptic transmission, synaptic or extrasynaptic AMPA-receptor levels, or other AMPA-receptor trafficking events. Moreover, expression of dominant-negative mutant synaptotagmin-1 that inhibited Ca2+-dependent presynaptic vesicle exocytosis also blocked Ca2+-dependent postsynaptic AMPA-receptor exocytosis, thereby abolishing LTP. Our results suggest that postsynaptic synaptotagmin-1 and synaptotagmin-7 act as redundant Ca2+-sensors for Ca2+-dependent exocytosis of AMPA-receptors during LTP, thus delineating a simple mechanism for the recruitment of AMPA-receptors that mediates LTP.
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Affiliation(s)
- Dick Wu
- Department of Molecular &Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305, USA.,Nancy Pritzker Laboratory, Stanford University Medical School, Stanford, California 94305, USA.,Department of Psychiatry &Behavioral Sciences, Stanford University Medical School, Stanford, California 94305, USA
| | - Taulant Bacaj
- Department of Molecular &Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305, USA
| | - Wade Morishita
- Nancy Pritzker Laboratory, Stanford University Medical School, Stanford, California 94305, USA.,Department of Psychiatry &Behavioral Sciences, Stanford University Medical School, Stanford, California 94305, USA
| | - Debanjan Goswami
- Nancy Pritzker Laboratory, Stanford University Medical School, Stanford, California 94305, USA.,Department of Psychiatry &Behavioral Sciences, Stanford University Medical School, Stanford, California 94305, USA
| | - Kristin L Arendt
- Department of Neurosurgery, Stanford University Medical School, Stanford, California 94305, USA
| | - Wei Xu
- Department of Molecular &Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305, USA
| | - Lu Chen
- Department of Neurosurgery, Stanford University Medical School, Stanford, California 94305, USA
| | - Robert C Malenka
- Nancy Pritzker Laboratory, Stanford University Medical School, Stanford, California 94305, USA.,Department of Psychiatry &Behavioral Sciences, Stanford University Medical School, Stanford, California 94305, USA
| | - Thomas C Südhof
- Department of Molecular &Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305, USA
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188
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Gundersen CB. The Structure of the Synaptic Vesicle-Plasma Membrane Interface Constrains SNARE Models of Rapid, Synchronous Exocytosis at Nerve Terminals. Front Mol Neurosci 2017; 10:48. [PMID: 28280457 PMCID: PMC5321675 DOI: 10.3389/fnmol.2017.00048] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2016] [Accepted: 02/13/2017] [Indexed: 12/27/2022] Open
Abstract
Contemporary models of neurotransmitter release invoke direct or indirect interactions between the Ca2+ sensor, synaptotagmin and the incompletely zippered soluble, N-ethyl-maleimide-sensitive factor attachment protein receptor (SNARE) complex. However, recent electron microscopic (EM) investigations have raised pragmatic issues concerning the mechanism by which SNAREs trigger membrane fusion at nerve terminals. The first issue is related to the finding that the area of contact between a “fully primed” synaptic vesicle and the plasma membrane can exceed 600 nm2. Approximately four-thousands lipid molecules can inhabit this contact zone. Thus, renewed efforts will be needed to explain how the zippering of as few as two SNARE complexes mobilizes these lipids to achieve membrane fusion. The second issue emerges from the finding that “docking filaments” are sandwiched within the area of vesicle-plasma membrane contact. It is challenging to reconcile the location of these filaments with SNARE models of exocytosis. Instead, this commentary outlines how these data are more compatible with a model in which a cluster of synaptotagmins catalyzes exocytotic membrane fusion.
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Affiliation(s)
- Cameron B Gundersen
- Department of Molecular and Medical Pharmacology, David Geffen UCLA School of Medicine Los Angeles, CA, USA
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189
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Guo T, Duan Z, Chen J, Xie C, Wang Y, Chen P, Wang X. Pull-down combined with proteomic strategy reveals functional diversity of synaptotagmin I. PeerJ 2017; 5:e2973. [PMID: 28194317 PMCID: PMC5301975 DOI: 10.7717/peerj.2973] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Accepted: 01/10/2017] [Indexed: 12/05/2022] Open
Abstract
Synaptotagmin I (Syt I) is most abundant in the brain and is involved in multiple cellular processes. Its two C2 domains, C2A and C2B, are the main functional regions. Our present study employed a pull-down combined with proteomic strategy to identify the C2 domain-interacting proteins to comprehensively understand the biological roles of the C2 domains and thus the functional diversity of Syt I. A total of 135 non-redundant proteins interacting with the C2 domains of Syt I were identified. Out of them, 32 and 64 proteins only bound to C2A or C2B domains, respectively, and 39 proteins bound to both of them. Compared with C2A, C2B could bind to many more proteins particularly those involved in synaptic transmission and metabolic regulation. Functional analysis indicated that Syt I may exert impacts by interacting with other proteins on multiple cellular processes, including vesicular membrane trafficking, synaptic transmission, metabolic regulation, catalysis, transmembrane transport and structure formation, etc. These results demonstrate that the functional diversity of Syt I is higher than previously expected, that its two domains may mediate the same and different cellular processes cooperatively or independently, and that C2B domain may play even more important roles than C2A in the functioning of Syt I. This work not only further deepened our understanding of the functional diversity of Syt I and the functional differences between its two C2 domains, but also provided important clues for the further related researches.
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Affiliation(s)
- Tianyao Guo
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
| | - Zhigui Duan
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
| | - Jia Chen
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
| | - Chunliang Xie
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
| | - Ying Wang
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
| | - Ping Chen
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
| | - Xianchun Wang
- Key Laboratory of Protein Chemistry and Developmental Biology of Ministry of Education, College of Life Sciences, Hunan Normal University , Changsha , Hunan , P. R. of China
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190
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Kennedy MB. Biochemistry and neuroscience: the twain need to meet. Curr Opin Neurobiol 2017; 43:79-86. [PMID: 28160757 DOI: 10.1016/j.conb.2017.01.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Revised: 01/12/2017] [Accepted: 01/12/2017] [Indexed: 10/20/2022]
Abstract
Neuroscience has come to mean the study of electrophysiology of neurons and synapses, micro and macro-scale neuroanatomy, and the functional organization of brain areas. The molecular axis of the field, as reflected in textbooks, often includes only descriptions of the structure and function of individual channels and receptor proteins, and the extracellular signals that guide development and repair. Studies of cytosolic 'molecular machines', large assemblies of proteins that orchestrate regulation of neuronal functions, have been neglected. However, a complete understanding of brain function that will enable new strategies for treatment of the most intractable neural disorders will require that in vitro biochemical studies of molecular machines be reintegrated into the field of neuroscience.
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Affiliation(s)
- Mary B Kennedy
- Division of Biology and Biochemical Engineering, Mail Code 216-76, California Institute of Technology, Pasadena, CA 91125, United States.
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191
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Han J, Pluhackova K, Böckmann RA. The Multifaceted Role of SNARE Proteins in Membrane Fusion. Front Physiol 2017; 8:5. [PMID: 28163686 PMCID: PMC5247469 DOI: 10.3389/fphys.2017.00005] [Citation(s) in RCA: 178] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 01/04/2017] [Indexed: 12/28/2022] Open
Abstract
Membrane fusion is a key process in all living organisms that contributes to a variety of biological processes including viral infection, cell fertilization, as well as intracellular transport, and neurotransmitter release. In particular, the various membrane-enclosed compartments in eukaryotic cells need to exchange their contents and communicate across membranes. Efficient and controllable fusion of biological membranes is known to be driven by cooperative action of SNARE proteins, which constitute the central components of the eukaryotic fusion machinery responsible for fusion of synaptic vesicles with the plasma membrane. During exocytosis, vesicle-associated v-SNARE (synaptobrevin) and target cell-associated t-SNAREs (syntaxin and SNAP-25) assemble into a core trans-SNARE complex. This complex plays a versatile role at various stages of exocytosis ranging from the priming to fusion pore formation and expansion, finally resulting in the release or exchange of the vesicle content. This review summarizes current knowledge on the intricate molecular mechanisms underlying exocytosis triggered and catalyzed by SNARE proteins. Particular attention is given to the function of the peptidic SNARE membrane anchors and the role of SNARE-lipid interactions in fusion. Moreover, the regulatory mechanisms by synaptic auxiliary proteins in SNARE-driven membrane fusion are briefly outlined.
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Affiliation(s)
- Jing Han
- Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science CenterXi'an, China; Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-NürnbergErlangen, Germany
| | - Kristyna Pluhackova
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
| | - Rainer A Böckmann
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
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192
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Kaeser PS, Regehr WG. The readily releasable pool of synaptic vesicles. Curr Opin Neurobiol 2017; 43:63-70. [PMID: 28103533 DOI: 10.1016/j.conb.2016.12.012] [Citation(s) in RCA: 143] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 11/26/2016] [Accepted: 12/31/2016] [Indexed: 10/20/2022]
Abstract
Each presynaptic bouton is densely packed with many vesicles, only a small fraction of which are available for immediate release. These vesicles constitute the readily releasable pool (RRP). The RRP size, and the probability of release of each vesicle within the RRP, together determine synaptic strength. Here, we discuss complications and recent advances in determining the size of the physiologically relevant RRP. We consider molecular mechanisms to generate and regulate the RRP, and discuss the relationship between vesicle docking and the RRP. We conclude that many RRP vesicles are docked, that some docked vesicles may not be part of the RRP, and that undocked vesicles can contribute to the RRP by rapid recruitment to unoccupied, molecularly activated ready-to-release sites.
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Affiliation(s)
- Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, United States.
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, United States.
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193
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Abstract
The intense X-ray pulses from free-electron lasers, of only femtoseconds duration, outrun most of the processes that lead to structural degradation in X-ray exposures of macromolecules. Using these sources it is therefore possible to increase the dose to macromolecular crystals by several orders of magnitude higher than usually tolerable in conventional measurements, allowing crystal size to be decreased dramatically in diffraction measurements and without the need to cool the sample. Such pulses lead to the eventual vaporization of the sample, which has required a measurement approach, called serial crystallography, of consolidating snapshot diffraction patterns of many individual crystals. This in turn has further separated the connection between dose and obtainable diffraction information, with the only requirement from a single pattern being that to give enough information to place it, in three-dimensional reciprocal space, in relation to other patterns. Millions of extremely weak patterns can be collected and combined in this way, requiring methods to rapidly replenish the sample into the beam while generating the lowest possible background . The method is suited to time-resolved measurements over timescales below 1 ps to several seconds, and opens new opportunities for phasing. Some straightforward considerations of achievable signal levels are discussed and compared with a wide variety of recent experiments carried out at XFEL, synchrotron, and even laboratory sources, to discuss the capabilities of these new approaches and give some perspectives on their further development.
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Affiliation(s)
- Henry N Chapman
- Center for Free-Electron Laser Science, DESY, Hamburg, 22607, Germany.
- Department of Physics, University of Hamburg, Hamburg, 22607, Germany.
- The Centre for Ultrafast Imaging, University of Hamburg, Hamburg, 22607, Germany.
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194
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Abstract
Coiled coils appear in countless structural contexts, as appendages to small proteins, as parts of multi-domain proteins, and as building blocks of filaments. Although their structure is unpretentious and their basic properties are understood in great detail, the spectrum of functional properties they provide in different proteins has become increasingly complex. This chapter aims to depict this functional spectrum, to identify common themes and their molecular basis, with an emphasis on new insights gained into dynamic aspects.
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Affiliation(s)
- Marcus D Hartmann
- Max Planck Institute for Developmental Biology, Spemannstraße 35, 72076, Tübingen, Germany.
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195
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Pan YZ, Quade B, Brewer KD, Szabo M, Swarbrick JD, Graham B, Rizo J. Sequence-specific assignment of methyl groups from the neuronal SNARE complex using lanthanide-induced pseudocontact shifts. JOURNAL OF BIOMOLECULAR NMR 2016; 66:281-293. [PMID: 27988858 PMCID: PMC5216067 DOI: 10.1007/s10858-016-0078-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Accepted: 11/24/2016] [Indexed: 05/03/2023]
Abstract
Neurotransmitter release depends critically on the neuronal SNARE complex formed by syntaxin-1, SNAP-25 and synaptobrevin, as well as on other proteins such as Munc18-1, Munc13-1 and synaptotagmin-1. Although three-dimensional structures are available for these components, it is still unclear how they are assembled between the synaptic vesicle and plasma membranes to trigger fast, Ca2+-dependent membrane fusion. Methyl TROSY NMR experiments provide a powerful tool to study complexes between these proteins, but assignment of the methyl groups of the SNARE complex is hindered by its limited solubility. Here we report the assignment of the isoleucine, leucine, methionine and valine methyl groups of the four SNARE motifs of syntaxin-1, SNAP-25 and synaptobrevin within the SNARE complex based solely on measurements of lanthanide-induced pseudocontact shifts. Our results illustrate the power of this approach to assign protein resonances without the need of triple resonance experiments and provide an invaluable tool for future structural studies of how the SNARE complex binds to other components of the release machinery.
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Affiliation(s)
- Yun-Zu Pan
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Bradley Quade
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Kyle D Brewer
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Monika Szabo
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, Australia
| | - James D Swarbrick
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, Australia
| | - Bim Graham
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, Australia
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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196
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Stability, folding dynamics, and long-range conformational transition of the synaptic t-SNARE complex. Proc Natl Acad Sci U S A 2016; 113:E8031-E8040. [PMID: 27911771 DOI: 10.1073/pnas.1605748113] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Synaptic soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) couple their stepwise folding to fusion of synaptic vesicles with plasma membranes. In this process, three SNAREs assemble into a stable four-helix bundle. Arguably, the first and rate-limiting step of SNARE assembly is the formation of an activated binary target (t)-SNARE complex on the target plasma membrane, which then zippers with the vesicle (v)-SNARE on the vesicle to drive membrane fusion. However, the t-SNARE complex readily misfolds, and its structure, stability, and dynamics are elusive. Using single-molecule force spectroscopy, we modeled the synaptic t-SNARE complex as a parallel three-helix bundle with a small frayed C terminus. The helical bundle sequentially folded in an N-terminal domain (NTD) and a C-terminal domain (CTD) separated by a central ionic layer, with total unfolding energy of ∼17 kBT, where kB is the Boltzmann constant and T is 300 K. Peptide binding to the CTD activated the t-SNARE complex to initiate NTD zippering with the v-SNARE, a mechanism likely shared by the mammalian uncoordinated-18-1 protein (Munc18-1). The NTD zippering then dramatically stabilized the CTD, facilitating further SNARE zippering. The subtle bidirectional t-SNARE conformational switch was mediated by the ionic layer. Thus, the t-SNARE complex acted as a switch to enable fast and controlled SNARE zippering required for synaptic vesicle fusion and neurotransmission.
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197
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Pinheiro PS, Houy S, Sørensen JB. C2-domain containing calcium sensors in neuroendocrine secretion. J Neurochem 2016; 139:943-958. [DOI: 10.1111/jnc.13865] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/17/2016] [Accepted: 10/05/2016] [Indexed: 12/11/2022]
Affiliation(s)
- Paulo S. Pinheiro
- Center for Neuroscience and Cell Biology; University of Coimbra; Coimbra Portugal
| | - Sébastien Houy
- Department of Neuroscience and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Jakob B. Sørensen
- Department of Neuroscience and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
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198
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C-terminal domain of mammalian complexin-1 localizes to highly curved membranes. Proc Natl Acad Sci U S A 2016; 113:E7590-E7599. [PMID: 27821736 DOI: 10.1073/pnas.1609917113] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In presynaptic nerve terminals, complexin regulates spontaneous "mini" neurotransmitter release and activates Ca2+-triggered synchronized neurotransmitter release. We studied the role of the C-terminal domain of mammalian complexin in these processes using single-particle optical imaging and electrophysiology. The C-terminal domain is important for regulating spontaneous release in neuronal cultures and suppressing Ca2+-independent fusion in vitro, but it is not essential for evoked release in neuronal cultures and in vitro. This domain interacts with membranes in a curvature-dependent fashion similar to a previous study with worm complexin [Snead D, Wragg RT, Dittman JS, Eliezer D (2014) Membrane curvature sensing by the C-terminal domain of complexin. Nat Commun 5:4955]. The curvature-sensing value of the C-terminal domain is comparable to that of α-synuclein. Upon replacement of the C-terminal domain with membrane-localizing elements, preferential localization to the synaptic vesicle membrane, but not to the plasma membrane, results in suppression of spontaneous release in neurons. Membrane localization had no measurable effect on evoked postsynaptic currents of AMPA-type glutamate receptors, but mislocalization to the plasma membrane increases both the variability and the mean of the synchronous decay time constant of NMDA-type glutamate receptor evoked postsynaptic currents.
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Pérez-Lara Á, Thapa A, Nyenhuis SB, Nyenhuis DA, Halder P, Tietzel M, Tittmann K, Cafiso DS, Jahn R. PtdInsP 2 and PtdSer cooperate to trap synaptotagmin-1 to the plasma membrane in the presence of calcium. eLife 2016; 5. [PMID: 27791979 PMCID: PMC5123861 DOI: 10.7554/elife.15886] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Accepted: 10/25/2016] [Indexed: 12/16/2022] Open
Abstract
The Ca2+-sensor synaptotagmin-1 that triggers neuronal exocytosis binds to negatively charged membrane lipids (mainly phosphatidylserine (PtdSer) and phosphoinositides (PtdIns)) but the molecular details of this process are not fully understood. Using quantitative thermodynamic, kinetic and structural methods, we show that synaptotagmin-1 (from Rattus norvegicus and expressed in Escherichia coli) binds to PtdIns(4,5)P2 via a polybasic lysine patch in the C2B domain, which may promote the priming or docking of synaptic vesicles. Ca2+ neutralizes the negative charges of the Ca2+-binding sites, resulting in the penetration of synaptotagmin-1 into the membrane, via binding of PtdSer, and an increase in the affinity of the polybasic lysine patch to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2). These Ca2+-induced events decrease the dissociation rate of synaptotagmin-1 membrane binding while the association rate remains unchanged. We conclude that both membrane penetration and the increased residence time of synaptotagmin-1 at the plasma membrane are crucial for triggering exocytotic membrane fusion. DOI:http://dx.doi.org/10.7554/eLife.15886.001 The human nervous system contains billions of neurons that communicate with each other across junctions called synapses. When a neuron is activated, the levels of calcium ions inside the cell rise. This causes molecules called neurotransmitters to be released from the neuron at a synapse to make contact with the second neuron. The neurotransmitters are stored inside cells within compartments known as synaptic vesicles and are released when these vesicles fuse with the membrane surrounding the cell. Proteins called SNAREs regulate the membrane fusion process. These proteins assemble into bundles that help to drive vesicle and cell membranes together. Another protein called synaptotagmin-1 sticks out from the vesicle membrane and senses the levels of calcium ions in the cell to trigger membrane fusion at the right time. Synaptotagmin-1 has two regions that can bind to calcium ions, known as the C2 domains. When calcium ion levels rise, these domains insert into the cell membrane by binding to two fat molecules in the membrane called phosphatidylserine (PtdSer) and phosphatidylinositol 4,5-bisphosphate (PtdInsP2). Synaptotagmin-1 also interacts with the SNARE proteins, but it is not known whether synaptotagmin-1 triggers fusion by binding directly to SNAREs, or by the way it inserts into the cell membrane. Pérez-Lara et al. used several biophysical methods to investigate how synaptotagmin-1 binds to PtdSer and PtdInsP2. The experiments show that these molecules bind to different regions of synaptotagmin-1 and work together to attach the protein to the cell membrane and insert the C2 domains. Calcium ions increase the affinity of synaptotagmin-1 binding to the cell membrane by making it harder for synaptotagmin-1 to separate from the membrane, rather than by increasing its ability to bind to it. Further experiments show that synaptotagmin-1 prefers to bind to membranes that contain PtdInsP2 over binding to the SNARE proteins. Together, the findings of Pérez-Lara et al. suggest that calcium ions may trigger the release of neurotransmitters by trapping synaptotagmin-1 at the cell membrane rather than by directly affecting how it interacts with SNARE proteins. Further work will be needed to establish exactly how the SNARE proteins, PtdInsP2 and synaptotagmin-1 interact. DOI:http://dx.doi.org/10.7554/eLife.15886.002
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Affiliation(s)
- Ángel Pérez-Lara
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Anusa Thapa
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
| | - Sarah B Nyenhuis
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
| | - David A Nyenhuis
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
| | - Partho Halder
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Michael Tietzel
- Department of Molecular Enzymology, Göttingen Center for Molecular Biosciences, Georg-August University Göttingen, Göttingen, Germany
| | - Kai Tittmann
- Department of Molecular Enzymology, Göttingen Center for Molecular Biosciences, Georg-August University Göttingen, Göttingen, Germany
| | - David S Cafiso
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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Lyubimov AY, Uervirojnangkoorn M, Zeldin OB, Zhou Q, Zhao M, Brewster AS, Michels-Clark T, Holton JM, Sauter NK, Weis WI, Brunger AT. Advances in X-ray free electron laser (XFEL) diffraction data processing applied to the crystal structure of the synaptotagmin-1 / SNARE complex. eLife 2016; 5. [PMID: 27731796 PMCID: PMC5094853 DOI: 10.7554/elife.18740] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Accepted: 10/11/2016] [Indexed: 12/03/2022] Open
Abstract
X-ray free electron lasers (XFELs) reduce the effects of radiation damage on macromolecular diffraction data and thereby extend the limiting resolution. Previously, we adapted classical post-refinement techniques to XFEL diffraction data to produce accurate diffraction data sets from a limited number of diffraction images (Uervirojnangkoorn et al., 2015), and went on to use these techniques to obtain a complete data set from crystals of the synaptotagmin-1 / SNARE complex and to determine the structure at 3.5 Å resolution (Zhou et al., 2015). Here, we describe new advances in our methods and present a reprocessed XFEL data set of the synaptotagmin-1 / SNARE complex. The reprocessing produced small improvements in electron density maps and the refined atomic model. The maps also contained more information than those of a lower resolution (4.1 Å) synchrotron data set. Processing a set of simulated XFEL diffraction images revealed that our methods yield accurate data and atomic models. DOI:http://dx.doi.org/10.7554/eLife.18740.001
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Affiliation(s)
- Artem Y Lyubimov
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Neurology and Neurological Science, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States.,Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Monarin Uervirojnangkoorn
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Neurology and Neurological Science, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Oliver B Zeldin
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Neurology and Neurological Science, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Neurology and Neurological Science, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Minglei Zhao
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Neurology and Neurological Science, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Aaron S Brewster
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States
| | - Tara Michels-Clark
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States
| | - James M Holton
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States.,Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, United States.,Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | - Nicholas K Sauter
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States
| | - William I Weis
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States
| | - Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States.,Neurology and Neurological Science, Stanford University, Stanford, United States.,Photon Science, Stanford University, Stanford, United States.,Structural Biology, Stanford University, Stanford, United States.,Howard Hughes Medical Institute, Stanford University, Stanford, United States
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