1
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Tammareddy T, Keyrouz W, Sriram RD, Pant HC, Cardone A, Klauda JB. Investigation of the Effect of Peptide p5 Targeting CDK5-p25 Hyperactivity on Munc18-1 (P67) Regulating Neuronal Exocytosis Using Molecular Simulations. Biochemistry 2024; 63:1837-1857. [PMID: 38953497 DOI: 10.1021/acs.biochem.4c00148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/04/2024]
Abstract
Munc18-1 is an SM (sec1/munc-like) family protein involved in vesicle fusion and neuronal exocytosis. Munc18-1 is known to regulate the exocytosis process by binding with closed- and open-state conformations of Syntaxin1, a protein belonging to the SNARE family established to be central to the exocytosis process. Our previous work studied peptide p5 as a promising drug candidate for CDK5-p25 complex, an Alzheimer's disease (AD) pathological target. Experimental in vivo and in vitro studies suggest that Munc18-1 promotes p5 to selectively inhibit the CDK5-p25 complex without affecting the endogenous CDK5 activity, a characteristic of remarkable therapeutic implications. In this paper, we identify several binding modes of p5 with Munc18-1 that could potentially affect the Munc18-1 binding with SNARE proteins and lead to off-target effects on neuronal communication using molecular dynamics simulations. Recent studies indicate that disruption of Munc18-1 function not only disrupts neurotransmitter release but also results in neurodegeneration, exhibiting clinical resemblance to other neurodegenerative conditions such as AD, causing diagnostic and treatment challenges. We characterize such interactions between p5 and Munc18-1, define the corresponding pharmacophores, and provide guidance for the in vitro validation of our findings to improve therapeutic efficacy and safety of p5.
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Affiliation(s)
- Tejaswi Tammareddy
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
| | | | | | - Harish C Pant
- Neuronal Cytoskeletal Protein Regulation Section, Laboratory of Neurochemistry, NINDS, Bethesda, Maryland 20892, United States
| | | | - Jeffery B Klauda
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States
- Institute for Physical Science & Technology, Biophysics Graduate Program, University of Maryland, College Park, Maryland 20742, United States
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2
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Duan M, Plemel RL, Takenaka T, Lin A, Delgado BM, Nattermann U, Nickerson DP, Mima J, Miller EA, Merz AJ. SNARE chaperone Sly1 directly mediates close-range vesicle tethering. J Cell Biol 2024; 223:e202001032. [PMID: 38478018 PMCID: PMC10943277 DOI: 10.1083/jcb.202001032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 12/20/2023] [Accepted: 02/22/2024] [Indexed: 03/17/2024] Open
Abstract
The essential Golgi protein Sly1 is a member of the Sec1/mammalian Unc-18 (SM) family of SNARE chaperones. Sly1 was originally identified through remarkable gain-of-function alleles that bypass requirements for diverse vesicle tethering factors. Employing genetic analyses and chemically defined reconstitutions of ER-Golgi fusion, we discovered that a loop conserved among Sly1 family members is not only autoinhibitory but also acts as a positive effector. An amphipathic lipid packing sensor (ALPS)-like helix within the loop directly binds high-curvature membranes. Membrane binding is required for relief of Sly1 autoinhibition and also allows Sly1 to directly tether incoming vesicles to the Qa-SNARE on the target organelle. The SLY1-20 mutation bypasses requirements for diverse tethering factors but loses this ability if the tethering activity is impaired. We propose that long-range tethers, including Golgins and multisubunit tethering complexes, hand off vesicles to Sly1, which then tethers at close range to initiate trans-SNARE complex assembly and fusion in the early secretory pathway.
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Affiliation(s)
- Mengtong Duan
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - Rachael L. Plemel
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | | | - Ariel Lin
- Department of Biochemistry, University of Washington, Seattle, WA, USA
- Department of Biology, California State University, San Bernardino, CA, USA
| | | | - Una Nattermann
- Department of Biochemistry, University of Washington, Seattle, WA, USA
- Biophysics, Structure, and Design Graduate Program, University of Washington, Seattle, WA, USA
- Institute for Protein Design, University of Washington, Seattle, WA, USA
| | | | - Joji Mima
- Institute for Protein Research, Osaka University, Osaka, Japan
| | | | - Alexey J. Merz
- Department of Biochemistry, University of Washington, Seattle, WA, USA
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3
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Jahn R, Cafiso DC, Tamm LK. Mechanisms of SNARE proteins in membrane fusion. Nat Rev Mol Cell Biol 2024; 25:101-118. [PMID: 37848589 DOI: 10.1038/s41580-023-00668-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2023] [Indexed: 10/19/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of small conserved eukaryotic proteins that mediate membrane fusion between organelles and with the plasma membrane. SNAREs are directly or indirectly anchored to membranes. Prior to fusion, complementary SNAREs assemble between membranes with the aid of accessory proteins that provide a scaffold to initiate SNARE zippering, pulling the membranes together and mediating fusion. Recent advances have enabled the construction of detailed models describing bilayer transitions and energy barriers along the fusion pathway and have elucidated the structures of SNAREs complexed in various states with regulatory proteins. In this Review, we discuss how these advances are yielding an increasingly detailed picture of the SNARE-mediated fusion pathway, leading from first contact between the membranes via metastable non-bilayer intermediates towards the opening and expansion of a fusion pore. We describe how SNARE proteins assemble into complexes, how this assembly is regulated by accessory proteins and how SNARE complexes overcome the free energy barriers that prevent spontaneous membrane fusion.
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Affiliation(s)
- Reinhard Jahn
- Laboratory of Neurobiology, Max-Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - David C Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
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4
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Ru Y, Dong S, Liu J, Liu J, Eyden B. Structural characterization and origin of surface vesicles in monocytes: another membranous pathway from cytoplasm to cell surface. Ultrastruct Pathol 2024; 48:56-65. [PMID: 38037244 DOI: 10.1080/01913123.2023.2286972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2023] [Accepted: 11/20/2023] [Indexed: 12/02/2023]
Abstract
The monocytes in acute monocytic leukemia (AML-M5b) were analyzed by scanning and transmission electron microscopy (SEM and TEM) to understand more fully their structure and origin. By SEM, monocytes exhibited localized expansions of the surface, some of which appeared to bud off as surface vesicles (SVs). Filopodial processes and pseudopodia were also present. TEM demonstrated that the SVs were composed of a double-membrane at the pole away from the cell body, and a single membrane nearer to the cell body. In the peripheral cytoplasm, intracellular vesicles (IVs) had the appearance of vacuoles and were enclosed by single membranes. Most SVs were characterized by a notch as a rER edge and an expanded head. Filopodial processes had the same thickness of 40 nm as the SV walls, which suggested a close developmental relationship between the two. Pseudopodia between SVs were irregular in size. Rod-like rER cisternae were prominent in the peripheral cytoplasm and some showed a close physical juxtaposition as to suggest a transition from rER to IVs to SVs. Ultrastructural cytochemistry demonstrated activity of 5'-nucleotidase over rER, SVs, filopodial processes and pseudopodia, and a patchy reaction over other areas of plasma membrane. Overall, the results indicated that rER transforms into SVs, filopodial processes and pseudopodia, as a way of integrating cytoplasmic membranes into the plasma membrane.
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Affiliation(s)
- Yongxin Ru
- State Key Laboratory of Experimental Hematology, National Clinical Research Center for Blood Diseases, Haihe Laboratory of the Cell Ecosystem, Institute of Hematology&Blood Diseases Hospital, Chinese Academy of Medical Sciences &Peking Union Medical College, Tianjin, China
- Tianjin Institutes of Health Science, Tianjin, China
| | - Shuxu Dong
- State Key Laboratory of Experimental Hematology, National Clinical Research Center for Blood Diseases, Haihe Laboratory of the Cell Ecosystem, Institute of Hematology&Blood Diseases Hospital, Chinese Academy of Medical Sciences &Peking Union Medical College, Tianjin, China
- Tianjin Institutes of Health Science, Tianjin, China
| | - Jing Liu
- State Key Laboratory of Experimental Hematology, National Clinical Research Center for Blood Diseases, Haihe Laboratory of the Cell Ecosystem, Institute of Hematology&Blood Diseases Hospital, Chinese Academy of Medical Sciences &Peking Union Medical College, Tianjin, China
- Tianjin Institutes of Health Science, Tianjin, China
| | - Jinhua Liu
- State Key Laboratory of Experimental Hematology, National Clinical Research Center for Blood Diseases, Haihe Laboratory of the Cell Ecosystem, Institute of Hematology&Blood Diseases Hospital, Chinese Academy of Medical Sciences &Peking Union Medical College, Tianjin, China
- Tianjin Institutes of Health Science, Tianjin, China
| | - Brian Eyden
- Department of Histopathology, Christie NHS Foundation Trust, Manchester, UK
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5
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Karal MAS, Sultana S, Billah MM, Moniruzzaman M, Wadud MA, Gosh RC. Effects of polyethylene glycol-grafted phospholipid on the anionic magnetite nanoparticles-induced deformation and poration in giant lipid vesicles. PLoS One 2023; 18:e0289087. [PMID: 37523403 PMCID: PMC10389724 DOI: 10.1371/journal.pone.0289087] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 07/11/2023] [Indexed: 08/02/2023] Open
Abstract
The hydrophilic polymer polyethylene glycol-grafted phospholipid has been used extensively in the study of artificial vesicles, nanomedicine, and antimicrobial peptides/proteins. In this research, the effects of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N- [methoxy (polyethylene glycol)-2000] (abbreviated PEG-DOPE) on the deformation and poration of giant unilamellar vesicles (GUVs)-induced by anionic magnetite nanoparticles (NPs) have been investigated. For this, the size of the NPs used was 18 nm, and their concentration in the physiological solution was 2.00 μg/mL. GUVs were prepared using the natural swelling method comprising 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and PEG-DOPE. The mole% of PEG-DOPE in the membranes were 0, 2, and 5%. The degree of deformation of the GUVs was quantified by the parameter compactness (Com), which is 1.0 for the spherical-shaped GUVs. The value of Com increases with time during the interactions of NPs with GUVs for any concentration of PEG-DOPE, but the rate of increase is significantly influenced by the PEG-DOPE concentration in the membranes. The average compactness increases with the increase of PEG-DOPE%, and after 60 min of NPs interaction, the values of average compactness for 0, 2, and 5% PEG-DOPE were 1.19 ± 0.02, 1.26 ± 0.03 and 1.35 ± 0.05, respectively. The fraction of deformation (Frd) also increased with the increase of PEG-DOPE%, and at 60 min, the values of Frd for 0 and 5% PEG-DOPE were 0.47 ± 0.02 and 0.63 ± 0.02, respectively. The fraction of poration (Frp) increased with the increase of PEG-DOPE, and at 60 min, the values of Frp for 0 and 5% PEG-DOPE were 0.25 ± 0.02 and 0.48 ± 0.02, respectively. Hence, the presence of PEG-grafted phospholipid in the membranes greatly enhances the anionic magnetite NPs-induced deformation and poration of giant vesicles.
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Affiliation(s)
| | - Sharmin Sultana
- Department of Physics, University of Dhaka, Dhaka, Bangladesh
| | - Md Masum Billah
- Department of Physics, Jashore University of Science and Technology, Jashore, Bangladesh
| | - Md Moniruzzaman
- Department of Physics, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
| | - Md Abdul Wadud
- Department of Physics, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
| | - R C Gosh
- Department of Physics, University of Dhaka, Dhaka, Bangladesh
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6
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Frey F, Idema T. Membrane area gain and loss during cytokinesis. Phys Rev E 2022; 106:024401. [PMID: 36110005 DOI: 10.1103/physreve.106.024401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 07/19/2022] [Indexed: 06/15/2023]
Abstract
In cytokinesis of animal cells, the cell is symmetrically divided into two. Since the cell's volume is conserved, the projected area has to increase to allow for the change of shape. Here we aim to predict how membrane gain and loss adapt during cytokinesis. We work with a kinetic model in which membrane turnover depends on membrane tension and cell shape. We apply this model to a series of calculated vesicle shapes as a proxy for the shape of dividing cells. We find that the ratio of kinetic turnover parameters changes nonmonotonically with cell shape, determined by the dependence of exocytosis and endocytosis on membrane curvature. Our results imply that controlling membrane turnover will be crucial for the successful division of artificial cells.
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Affiliation(s)
- Felix Frey
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Timon Idema
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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7
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Single-molecule manipulation of macromolecules on GUV or SUV membranes using optical tweezers. Biophys J 2021; 120:5454-5465. [PMID: 34813728 DOI: 10.1016/j.bpj.2021.11.2884] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 10/16/2021] [Accepted: 11/19/2021] [Indexed: 11/23/2022] Open
Abstract
Despite their wide applications in soluble macromolecules, optical tweezers have rarely been used to characterize the dynamics of membrane proteins, mainly due to the lack of model membranes compatible with optical trapping. Here, we examined optical trapping and mechanical properties of two potential model membranes, giant and small unilamellar vesicles (GUVs and SUVs, respectively) for studies of membrane protein dynamics. We found that optical tweezers can stably trap GUVs containing iodixanol with controlled membrane tension. The trapped GUVs with high membrane tension can serve as a force sensor to accurately detect reversible folding of a DNA hairpin or membrane binding of synaptotagmin-1 C2AB domain attached to the GUV. We also observed that SUVs are rigid enough to resist large pulling forces and are suitable for detecting protein conformational changes induced by force. Our methodologies may facilitate single-molecule manipulation studies of membrane proteins using optical tweezers.
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8
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Uwaguchi Y, Fujiwara K, Doi N. Switching ON of Transcription-Translation System Using GUV Fusion by Co-supplementation of Calcium with Long-Chain Polyethylene Glycol. Chembiochem 2021; 22:2319-2324. [PMID: 33971077 DOI: 10.1002/cbic.202100100] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 04/28/2021] [Indexed: 11/09/2022]
Abstract
Giant unilamellar vesicles (GUVs) have been used as a material for bottom-up synthetic biology. However, due to the semi-permeability of the membrane, the need for methods to fuse GUVs has increased. To this aim, methods that are simple and show low leakage during fusion are important. In this study, we report a method of GUV fusion by a divalent cation (Ca2+ ) enhanced with a long chain polyethylene glycol (PEG20k). The methods showed significant GUV fusion without leakage of internal components of GUVs and maintained cell-free transcription-translation ability inside the GUVs without external supplementation of macromolecules. We demonstrate that the Ca-PEG method can be applied for switching ON of transcription-translation in GUVs in a fusion-dependent manner. The method developed here can be applied to extend bottom-up synthetic biology and molecular robotics that use GUVs as a chassis.
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Affiliation(s)
- Yusuke Uwaguchi
- Department of Biosciences & Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
| | - Kei Fujiwara
- Department of Biosciences & Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
| | - Nobuhide Doi
- Department of Biosciences & Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
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9
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Abstract
Giant unilamellar vesicles (GUVs) have gained great popularity as mimicries for cellular membranes. As their sizes are comfortably above the optical resolution limit, and their lipid composition is easily controlled, they are ideal for quantitative light microscopic investigation of dynamic processes in and on membranes. However, reconstitution of functional proteins into the lumen or the GUV membrane itself has proven technically challenging. In recent years, a selection of techniques has been introduced that tremendously improve GUV-assay development and enable the precise investigation of protein-membrane interactions under well-controlled conditions. Moreover, due to these methodological advances, GUVs are considered important candidates as protocells in bottom-up synthetic biology. In this review, we discuss the state of the art of the most important vesicle production and protein encapsulation methods and highlight some key protein systems whose functional reconstitution has advanced the field.
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Affiliation(s)
- Thomas Litschel
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried 82152, Germany; ,
| | - Petra Schwille
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried 82152, Germany; ,
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10
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Bone marrow mesenchymal cells: polymorphism associated with transformation of rough endoplasmic reticulum. BLOOD SCIENCE 2020; 3:6-13. [PMID: 35399204 PMCID: PMC8975078 DOI: 10.1097/bs9.0000000000000062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 10/08/2020] [Indexed: 11/27/2022] Open
Abstract
To understand the behavior and function of bone-marrow mesenchymal cells (BMMCs), we overviewed the morphological presentation of BMMCs in bone-marrow granules (b-BMMCs), isolated BMMCs (i-BMMCs), and BMMCs (c-BMMCs) cultured in H4434 methylcellulose semisolid and MEM media. All samples were derived from bone-marrow aspirates of 30 patients with hematocytopenia. Light microscopy exhibited b-BMMCs and i-BMMCs characterized by abundant cytoplasm and irregular shape in bone-marrow smears, as well as c-BMMCs in culture conditions. Scanning electron microscopy demonstrated cultured c-BMMCs with a sheet-like feature enveloping hematopoietic cells. Transmission electron microscopy revealed b-BMMCs constructing a honeycomb-like structure by thin bifurcate processes among hematopoietic cells. Furthermore, i-BMMCs had bifurcate parapodiums on the surface and prominent rough endoplasmic reticulum (rER) connected with the plasmalemma of the parapodiums. The detailed images suggested that rER may serve as a membrane resource for plasmalemmal expansion in BMMCs in bone marrow.
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11
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Schmid YRF, Scheller L, Buchmann S, Dittrich PS. Calcium-Mediated Liposome Fusion to Engineer Giant Lipid Vesicles with Cytosolic Proteins and Reconstituted Mammalian Proteins. ACTA ACUST UNITED AC 2020; 4:e2000153. [PMID: 33084207 DOI: 10.1002/adbi.202000153] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 09/25/2020] [Indexed: 12/16/2022]
Abstract
Giant unilamellar lipid vesicles (GUVs) are widely used as model membrane systems and provide an excellent basis to construct artificial cells. To construct more sophisticated artificial cells, proteins-in particular membrane proteins-need to be incorporated in GUVs. However, current methods for protein reconstitution have limited throughput or are not generally applicable for all proteins because they depend on detergent solubilization. This limitation is addressed here by introducing calcium-mediated membrane fusion to transfer proteins between negatively charged GUVs and cell-derived plasma membrane vesicles (CDVs), derived from HEK293T cells overexpressing a membrane receptor protein. Fusion conditions are optimized using large unilamellar vesicles and GUVs containing phosphatidylserines and fusogenic lipids. The approach is then applied to induce lipid mixing and subsequent transfer of the overexpressed membrane receptor from CDVs into GUVs. The membrane receptor is detected by immunofluorescence on GUVs that underwent lipid mixing with CDVs. Those GUVs also exhibit esterase activity because cytosolic esterases entrapped in the CDVs are transferred during membrane fusion. Thus, content mixing is demonstrated. Using CDVs circumvents the need to purify or solubilize proteins. Moreover, calcium-mediated fusion allows transfer of lipids, water-soluble and membrane bound proteins in one step, resulting in a semi-synthetic cell.
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Affiliation(s)
- Yannick R F Schmid
- Department of Biosystems Science and Engineering, Bioanalytics Group, ETH Zürich, Mattenstrasse 26, Basel, CH-4058, Switzerland
| | - Leo Scheller
- Department of Biosystems Science and Engineering, Biotechnology and Bioengineering Group, ETH Zürich, Mattenstrasse 26, Basel, CH-4058, Switzerland
| | - Sebastian Buchmann
- Department of Biosystems Science and Engineering, Bioanalytics Group, ETH Zürich, Mattenstrasse 26, Basel, CH-4058, Switzerland
| | - Petra S Dittrich
- Department of Biosystems Science and Engineering, Bioanalytics Group, ETH Zürich, Mattenstrasse 26, Basel, CH-4058, Switzerland
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12
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Wang X, Gong J, Zhu L, Wang S, Yang X, Xu Y, Yang X, Ma C. Munc13 activates the Munc18-1/syntaxin-1 complex and enables Munc18-1 to prime SNARE assembly. EMBO J 2020; 39:e103631. [PMID: 32643828 PMCID: PMC7429736 DOI: 10.15252/embj.2019103631] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Revised: 05/20/2020] [Accepted: 06/02/2020] [Indexed: 11/09/2022] Open
Abstract
Priming of synaptic vesicles involves Munc13-catalyzed transition of the Munc18-1/syntaxin-1 complex to the SNARE complex in the presence of SNAP-25 and synaptobrevin-2; Munc13 drives opening of syntaxin-1 via the MUN domain while Munc18-1 primes SNARE assembly via domain 3a. However, the underlying mechanism remains unclear. In this study, we have identified a number of residues in domain 3a of Munc18-1 that are crucial for Munc13 and Munc18-1 actions in SNARE complex assembly and synaptic vesicle priming. Our results showed that two residues (Q301/K308) at the side of domain 3a mediate the interaction between the Munc18-1/syntaxin-1 complex and the MUN domain. This interaction enables the MUN domain to drive the opening of syntaxin-1 linker region, thereby leading to the extension of domain 3a and promoting synaptobrevin-2 binding. In addition, we identified two residues (K332/K333) at the bottom of domain 3a that mediate the interaction between Munc18-1 and the SNARE motif of syntaxin-1. This interaction ensures Munc18-1 to persistently associate with syntaxin-1 during the conformational change of syntaxin-1 from closed to open, which reinforces the role of Munc18-1 in templating SNARE assembly. Taken together, our data suggest a mechanism by which Munc13 activates the Munc18-1/syntaxin-1 complex and enables Munc18-1 to prime SNARE assembly.
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Affiliation(s)
- Xianping Wang
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Jihong Gong
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Le Zhu
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Xiaoyu Yang
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Yuanyuan Xu
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Xiaofei Yang
- Key Laboratory of Cognitive ScienceHubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & TreatmentLaboratory of Membrane Ion Channels and MedicineCollege of Biomedical EngineeringSouth‐Central University for NationalitiesWuhanChina
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
- Institute of Brain ResearchHuazhong University of Science and TechnologyWuhanChina
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13
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Controlled Peptide-Mediated Vesicle Fusion Assessed by Simultaneous Dual-Colour Time-Lapsed Fluorescence Microscopy. Sci Rep 2020; 10:3087. [PMID: 32080270 PMCID: PMC7033240 DOI: 10.1038/s41598-020-59926-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 01/31/2020] [Indexed: 12/03/2022] Open
Abstract
We have employed a model system, inspired by SNARE proteins, to facilitate membrane fusion between Giant Unilamellar Vesicles (GUVs) and Large Unilamellar Vesicles (LUVs) under physiological conditions. In this system, two synthetic lipopeptide constructs comprising the coiled-coil heterodimer-forming peptides K4, (KIAALKE)4, or E4, (EIAALEK)4, a PEG spacer of variable length, and a cholesterol moiety to anchor the peptides into the liposome membrane replace the natural SNARE proteins. GUVs are functionalized with one of the lipopeptide constructs and the fusion process is triggered by adding LUVs bearing the complementary lipopeptide. Dual-colour time lapse fluorescence microscopy was used to visualize lipid- and content-mixing. Using conventional confocal microscopy, lipid mixing was observed on the lipid bilayer of individual GUVs. In addition to lipid-mixing, content-mixing assays showed a low efficiency due to clustering of K4-functionalized LUVs on the GUVs target membranes. We showed that, through the use of the non-ionic surfactant Tween 20, content-mixing between GUVs and LUVs could be improved, meaning this system has the potential to be employed for drug delivery in biological systems.
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14
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Duan XL, Guo Z, He YT, Li YX, Liu YN, Bai HH, Li HL, Hu XD, Suo ZW. SNAP25/syntaxin4/VAMP2/Munc18-1 Complexes in Spinal Dorsal Horn Contributed to Inflammatory Pain. Neuroscience 2020; 429:203-212. [PMID: 31962145 DOI: 10.1016/j.neuroscience.2020.01.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 12/31/2019] [Accepted: 01/02/2020] [Indexed: 02/06/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) have been implicated in the trafficking of postsynaptic glutamate receptors, including N-methyl-d-aspartate (NMDA)-subtype glutamate receptors (NMDARs) that are critical for nociceptive plasticity and behavioral sensitization. However, the components of SNAREs complex involved in spinal nociceptive processing remain largely unknown. Here we found that SNAP25, syntaxin4, VAMP2 and Munc18-1 were localized at postsynaptic sites and formed the complex in the superficial lamina of spinal cord dorsal horn of rats. The complex formation between these SNAREs components were accelerated after intraplantar injection of complete Freund's adjuvant (CFA), pharmacological removal of GABAergic inhibition or activation of NMDAR in intact rats. The increased SNAP25/syntaxin4/VAMP2/Munc18-1 interaction facilitated the surface delivery and synaptic accumulation of NMDAR during inflammatory pain. Disruption of the molecular interaction between SNAP25 with its SNARE partners by using a blocking peptide derived from the C-terminus of SNAP25 effectively repressed the surface and synaptic accumulation of GluN2B-containing NMDARs in CFA-injected rats. This peptide also alleviated inflammatory mechanical allodynia and thermal hypersensitivity. These data suggested that SNAREs complex assembly in spinal cord dorsal horn was involved in the inflammatory pain hypersensitivity through promoting NMDAR synaptic trafficking.
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Affiliation(s)
- Xing-Lian Duan
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Zhen Guo
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Yong-Tao He
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Yin-Xia Li
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Yan-Ni Liu
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Hu-Hu Bai
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Hu-Ling Li
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Xiao-Dong Hu
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China
| | - Zhan-Wei Suo
- Department of Molecular Pharmacology, School of Pharmacy, Lanzhou University, Lanzhou, Gansu 730000, PR China.
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15
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Kamiya K, Osaki T, Takeuchi S. Formation of vesicles-in-a-vesicle with asymmetric lipid components using a pulsed-jet flow method. RSC Adv 2019; 9:30071-30075. [PMID: 35530244 PMCID: PMC9072116 DOI: 10.1039/c9ra04622d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 09/18/2019] [Indexed: 11/21/2022] Open
Abstract
Lipid distribution in intracellular vesicles is different from that in the plasma membrane of eukaryotic cells. The lipid components in the intracellular vesicles are composed of phosphatidylserine and phosphatidylethanolamine in the outer leaflet and phosphatidylcholine and sphingomyelin in the inner leaflet. The lipid asymmetricities both in the intracellular vesicle membrane and the plasma membrane contribute to synaptic transmission functions. In this study, we developed a cell-sized asymmetric lipid vesicle system containing small-sized asymmetric lipid vesicles (of diameter 200–1000 nm) (asymmetric vesicles-in-a-vesicle), emulating lipid components in the plasma membrane and intracellular vesicle membrane of eukaryotic cells, using microfluidic technology. We successfully constructed an artificial exocytosis system using the asymmetric vesicles-in-a-vesicle system. This asymmetric vesicles-in-a-vesicle system will be helpful in understanding the mechanisms of vesicle transport, such as neurotransmission and exocytosis. We develop a cell-sized asymmetric lipid vesicle system containing small-sized asymmetric lipid vesicles using microfluidic technology.![]()
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Affiliation(s)
- Koki Kamiya
- Artificial Cell Membrane Systems Group, Kanagawa Institute of Industrial Science and Technology 3-2-1 Sakado, Takatsu-ku Kawasaki Kanagawa 213-0012 Japan.,Division of Molecular Science, Graduate School of Science and Technology, Gunma University 1-5-1 Tenjin-cho Kiryu Gunma 376-8515 Japan
| | - Toshihisa Osaki
- Artificial Cell Membrane Systems Group, Kanagawa Institute of Industrial Science and Technology 3-2-1 Sakado, Takatsu-ku Kawasaki Kanagawa 213-0012 Japan
| | - Shoji Takeuchi
- Artificial Cell Membrane Systems Group, Kanagawa Institute of Industrial Science and Technology 3-2-1 Sakado, Takatsu-ku Kawasaki Kanagawa 213-0012 Japan.,Department of Mechano-Informatics, Graduate School of Information Science and Technology, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8656 Japan
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16
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Jonáš A, Kochanczyk M, Ramirez AD, Speidel M, Florin EL. Mechanical Contact Spectroscopy: Characterizing Nanoscale Adhesive Contacts via Thermal Forces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:5809-5820. [PMID: 30965006 DOI: 10.1021/acs.langmuir.8b04074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The adhesion of micro- and nanoparticles to solid substrates immersed in liquids is a problem of great scientific and technological importance. However, the quantitative characterization of such nanoscale adhesive contacts without rupturing them still presents a major experimental challenge. In this article, we introduce mechanical contact spectroscopy (MCS), an experimental technique for the nondestructive probing of particle adhesion in liquid environments. With MCS, the strength of adhesive contacts is inferred from residual position fluctuations of adherent particles excited by thermal forces. In particular, the strength of adhesion is correlated with the standard deviation of the particle lateral position x, with smaller position standard deviations [Formula: see text] indicating higher adhesive strength. For a given combination of particles, substrate, and immersion medium, the adhesion is characterized by the mechanical contact spectrum, which is a histogram of ξ values obtained from tracking an ensemble of adherent particles. Because the energy of thermal excitation at room temperature is very small in comparison to the typical total energy of adhesive contacts, the studied contacts remain in equilibrium during the measurement. Using MCS, we study the adhesion of micrometer-sized particles to planar solid substrates under a wide range of environmental conditions, including liquid immersion media of varying ionic strength and adhesion substrates with different chemical functionality of their surfaces. These experiments provide evidence that MCS is capable of reproducibly detecting minute changes in the particle-substrate work of adhesion while at the same time covering the range of adhesive contact strength relevant in the context of surface chemistry, biology, and microfabrication.
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Affiliation(s)
- Alexandr Jonáš
- The Czech Academy of Sciences , Institute of Scientific Instruments , Královopolská 147 , 61264 Brno , Czech Republic
| | - Martin Kochanczyk
- Center for Nonlinear Dynamics and Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States
| | - Alexandro D Ramirez
- Center for Nonlinear Dynamics and Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States
| | - Michael Speidel
- European Molecular Biology Laboratory , Meyerhofstrasse 1 , 69117 Heidelberg , Germany
| | - Ernst-Ludwig Florin
- Center for Nonlinear Dynamics and Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States
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17
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Ivanov I, Lira RB, Tang TYD, Franzmann T, Klosin A, da Silva LC, Hyman A, Landfester K, Lipowsky R, Sundmacher K, Dimova R. Directed Growth of Biomimetic Microcompartments. ACTA ACUST UNITED AC 2019; 3:e1800314. [PMID: 32648704 DOI: 10.1002/adbi.201800314] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Revised: 01/15/2019] [Indexed: 01/04/2023]
Abstract
Contemporary biological cells are sophisticated and highly compartmentalized. Compartmentalization is an essential principle of prebiotic life as well as a key feature in bottom-up synthetic biology research. In this review, the dynamic growth of compartments as an essential prerequisite for enabling self-reproduction as a fundamental life process is discussed. The micrometer-sized compartments are focused on due to their cellular dimensions. Two types of compartments are considered, membraneless droplets and membrane-bound microcompartments. Growth mechanisms of aqueous droplets such as protein (condensates) or macromolecule-rich droplets (aqueous two phase systems) and coacervates are discussed, for which growth occurs via Ostwald ripening or coalescence. For membrane-bound compartments, vesicles are considered, which are composed of fatty acids, lipids, or polymers, where directed growth can occur via fusion or uptake of material from the surrounding. The development of novel approaches for growth of biomimetic microcompartments can eventually be utilized to construct new synthetic cells.
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Affiliation(s)
- Ivan Ivanov
- Max Planck Institute for Dynamics of Complex Technical Systems, Process Systems Engineering, Sandtorstrasse 1, 39106, Magdeburg, Germany
| | - Rafael B Lira
- Max Planck Institute of Colloids and Interfaces, Theory and Bio-Systems, Science Park Golm, 14424, Potsdam, Germany
| | - T-Y Dora Tang
- Max Planck Institute of Molecular Cell Biology and Genetics, Organization of Cytoplasm & Dynamic Protocellular Systems, Pfotenhauerstrasse 108, 01307, Dresden, Germany
| | - Titus Franzmann
- Max Planck Institute of Molecular Cell Biology and Genetics, Organization of Cytoplasm & Dynamic Protocellular Systems, Pfotenhauerstrasse 108, 01307, Dresden, Germany
| | - Adam Klosin
- Max Planck Institute of Molecular Cell Biology and Genetics, Organization of Cytoplasm & Dynamic Protocellular Systems, Pfotenhauerstrasse 108, 01307, Dresden, Germany
| | - Lucas Caire da Silva
- Max Planck Institute for Polymer Research, Physical Chemistry of Polymers, Ackermannweg 10, 55128, Mainz, Germany
| | - Anthony Hyman
- Max Planck Institute of Molecular Cell Biology and Genetics, Organization of Cytoplasm & Dynamic Protocellular Systems, Pfotenhauerstrasse 108, 01307, Dresden, Germany
| | - Katharina Landfester
- Max Planck Institute for Polymer Research, Physical Chemistry of Polymers, Ackermannweg 10, 55128, Mainz, Germany
| | - Reinhard Lipowsky
- Max Planck Institute of Colloids and Interfaces, Theory and Bio-Systems, Science Park Golm, 14424, Potsdam, Germany
| | - Kai Sundmacher
- Max Planck Institute for Dynamics of Complex Technical Systems, Process Systems Engineering, Sandtorstrasse 1, 39106, Magdeburg, Germany
| | - Rumiana Dimova
- Max Planck Institute of Colloids and Interfaces, Theory and Bio-Systems, Science Park Golm, 14424, Potsdam, Germany
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18
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Lira RB, Robinson T, Dimova R, Riske KA. Highly Efficient Protein-free Membrane Fusion: A Giant Vesicle Study. Biophys J 2019; 116:79-91. [PMID: 30579564 PMCID: PMC6342729 DOI: 10.1016/j.bpj.2018.11.3128] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 11/14/2018] [Accepted: 11/19/2018] [Indexed: 12/18/2022] Open
Abstract
Membrane fusion is a ubiquitous process in biology and is a prerequisite for many intracellular delivery protocols relying on the use of liposomes as drug carriers. Here, we investigate in detail the process of membrane fusion and the role of opposite charges in a protein-free lipid system based on cationic liposomes (LUVs, large unilamellar vesicles) and anionic giant unilamellar vesicles (GUVs) composed of different palmitoyloleoylphosphatidylcholine (POPC)/palmitoyloleoylphosphatidylglycerol (POPG) molar ratios. By using a set of optical-microscopy- and microfluidics-based methods, we show that liposomes strongly dock to GUVs of pure POPC or low POPG fraction (up to 10 mol%) in a process mainly associated with hemifusion and membrane tension increase, commonly leading to GUV rupture. On the other hand, docked LUVs quickly and very efficiently fuse with negative GUVs of POPG fractions at or above 20 mol%, resulting in dramatic GUV area increase in a charge-dependent manner; the vesicle area increase is deduced from GUV electrodeformation. Importantly, both hemifusion and full fusion are leakage-free. Fusion efficiency is quantified by the lipid transfer from liposomes to GUVs using fluorescence resonance energy transfer (FRET), which leads to consistent results when compared to fluorescence-lifetime-based FRET. We develop an approach to deduce the final composition of single GUVs after fusion based on the FRET efficiency. The results suggest that fusion is driven by membrane charge and appears to proceed up to charge neutralization of the acceptor GUV.
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Affiliation(s)
- Rafael B Lira
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil; Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Tom Robinson
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.
| | - Karin A Riske
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil.
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19
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OSHIMA A, SUMITOMO K. Vesicle Fusion with Artificial Bilayer Lipid Membrane Induced by Electrostatic Interaction. BUNSEKI KAGAKU 2019. [DOI: 10.2116/bunsekikagaku.68.23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Azusa OSHIMA
- NTT Basic Research Laboratories, NTT Corporation
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20
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Fusion assays for model membranes: a critical review. ADVANCES IN BIOMEMBRANES AND LIPID SELF-ASSEMBLY 2019. [DOI: 10.1016/bs.abl.2019.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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21
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Methods of reconstitution to investigate membrane protein function. Methods 2018; 147:126-141. [DOI: 10.1016/j.ymeth.2018.02.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Accepted: 02/13/2018] [Indexed: 02/06/2023] Open
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22
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Hybrid cell reactor system from Escherichia coli protoplast cells and arrayed lipid bilayer chamber device. Sci Rep 2018; 8:11757. [PMID: 30082826 PMCID: PMC6078950 DOI: 10.1038/s41598-018-30231-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 07/25/2018] [Indexed: 11/09/2022] Open
Abstract
We developed a novel hybrid cell reactor system via functional fusion of single Escherichia coli protoplast cells, that are deficient in cell wall and expose plasma membrane, with arrayed lipid bilayer chambers on a device in order to incorporate the full set of cytosolic and membrane constituents into the artificial chambers. We investigated gene expression activity to represent the viability of the hybrid cell reactors: over 20% of hybrid cells showed gene expression activity from plasmid or mRNA. This suggests that the hybrid cell reactors retained fundamental activity of genetic information transduction. To expand the applicability of the hybrid cell reactors, we also developed the E. coli-in-E. coli cytoplasm system as an artificial parasitism system. Over 30% of encapsulated E. coli cells exhibited normal cell division, showing that hybrid cells can accommodate and cultivate living cells. This novel artificial cell reactor technology would enable unique approaches for synthetic cell researches such as reconstruction of living cell, artificial parasitism/symbiosis system, or physical simulation to test functionality of synthetic genome.
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23
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Kweon DH, Kong B, Shin YK. Search for a minimal machinery for Ca 2+-triggered millisecond neuroexocytosis. Neuroscience 2018; 420:4-11. [PMID: 30056116 DOI: 10.1016/j.neuroscience.2018.07.031] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 07/11/2018] [Accepted: 07/18/2018] [Indexed: 11/25/2022]
Abstract
Neurons have the remarkable ability to release a batch of neurotransmitters into the synapse immediately after an action potential. This signature event is made possible by the simultaneous fusion of a number of synaptic vesicles to the plasma membrane upon Ca2+ entry into the active zone. The outcomes of both cellular and in vitro studies suggest that soluble N-ethylmaleimide-sensitive-factor attachment protein receptors (SNAREs) and synaptotagmin 1 (Syt1) constitute the minimal fast exocytosis machinery in the neuron. Syt1 is the major Ca2+-sensor and orchestrates the synchronous start of individual vesicle fusion events while SNAREs are the membrane fusion machinery that dictates the kinetics of each single fusion event. The data also suggest that Ca2+-bound Syt1 is involved in the upstream docking step which leads to an increase in the number of fusion events or the size of the release, leaving the SNARE complex alone to carry out membrane fusion by themselves.
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Affiliation(s)
- Dae-Hyuk Kweon
- Department of Integrative Biotechnology, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Byoungjae Kong
- Department of Integrative Biotechnology, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Yeon-Kyun Shin
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, United States.
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24
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Piffoux M, Silva AKA, Wilhelm C, Gazeau F, Tareste D. Modification of Extracellular Vesicles by Fusion with Liposomes for the Design of Personalized Biogenic Drug Delivery Systems. ACS NANO 2018; 12:6830-6842. [PMID: 29975503 DOI: 10.1021/acsnano.8b02053] [Citation(s) in RCA: 249] [Impact Index Per Article: 41.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Extracellular vesicles (EVs) are recognized as nature's own carriers to transport macromolecules throughout the body. Hijacking this endogenous communication system represents an attractive strategy for advanced drug delivery. However, efficient and reproducible loading of EVs with therapeutic or imaging agents still represents a bottleneck for their use as a drug delivery system. Here, we developed a method for modifying cell-derived EVs through their fusion with liposomes containing both membrane and soluble cargoes. The fusion of EVs with functionalized liposomes was triggered by polyethylene glycol (PEG) to create smart biosynthetic hybrid vectors. This versatile method proved to be efficient to enrich EVs with exogenous lipophilic or hydrophilic compounds, while preserving their intrinsic content and biological properties. Hybrid EVs improved cellular delivery efficiency of a chemotherapeutic compound by a factor of 3-4, as compared to the free drug or the drug-loaded liposome precursor. On one side, this method allows the biocamouflage of liposomes by enriching their lipid bilayer and inner compartment with biogenic molecules. On the other side, the proposed fusion strategy enables efficient EV loading, and the pharmaceutical development of EVs with adaptable activity and drug delivery property.
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Affiliation(s)
- Max Piffoux
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - Amanda K A Silva
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - Claire Wilhelm
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - Florence Gazeau
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - David Tareste
- Institut Jacques Monod , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7592, F-75013 Paris , France
- Centre de Psychiatrie et Neurosciences , Université Paris Descartes, Sorbonne Paris Cité , INSERM UMR 894, F-75014 Paris , France
- Membrane Traffic in Health and Disease , Université Paris Descartes, Sorbonne Paris Cité , INSERM ERL U950, F-75014 Paris , France
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25
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A convenient protocol for generating giant unilamellar vesicles containing SNARE proteins using electroformation. Sci Rep 2018; 8:9422. [PMID: 29930377 PMCID: PMC6013450 DOI: 10.1038/s41598-018-27456-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 05/29/2018] [Indexed: 01/05/2023] Open
Abstract
Reconstitution of membrane proteins in artificial membranes is an essential prerequisite for functional studies that depend on the context of an intact membrane. While straight-forward protocols for reconstituting proteins in small unilamellar vesicles were developed many years ago, it is much more difficult to prepare large membranes containing membrane proteins at biologically relevant concentrations. Giant unilamellar vesicles (GUVs) represent a model system that is characterised by low curvature, controllable tension, and large surface that can be easily visualised with microscopy, but protein insertion is notoriously difficult. Here we describe a convenient method for efficient generation of GUVs containing functionally active SNARE proteins that govern exocytosis of synaptic vesicles. Preparation of proteo-GUVs requires a simple, in-house-built device, standard and inexpensive electronic equipment, and employs a straight-forward protocol that largely avoids damage of the proteins. The procedure allows upscaling and multiplexing, thus providing a platform for establishing and optimizing preparation of GUVs containing membrane proteins for a diverse array of applications.
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26
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Daste F, Sauvanet C, Bavdek A, Baye J, Pierre F, Le Borgne R, David C, Rojo M, Fuchs P, Tareste D. The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion. EMBO Rep 2018; 19:embr.201643637. [PMID: 29661855 DOI: 10.15252/embr.201643637] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 03/07/2018] [Accepted: 03/16/2018] [Indexed: 12/31/2022] Open
Abstract
Mitochondria are double-membrane-bound organelles that constantly change shape through membrane fusion and fission. Outer mitochondrial membrane fusion is controlled by Mitofusin, whose molecular architecture consists of an N-terminal GTPase domain, a first heptad repeat domain (HR1), two transmembrane domains, and a second heptad repeat domain (HR2). The mode of action of Mitofusin and the specific roles played by each of these functional domains in mitochondrial fusion are not fully understood. Here, using a combination of in situ and in vitro fusion assays, we show that HR1 induces membrane fusion and possesses a conserved amphipathic helix that folds upon interaction with the lipid bilayer surface. Our results strongly suggest that HR1 facilitates membrane fusion by destabilizing the lipid bilayer structure, notably in membrane regions presenting lipid packing defects. This mechanism for fusion is thus distinct from that described for the heptad repeat domains of SNARE and viral proteins, which assemble as membrane-bridging complexes, triggering close membrane apposition and fusion, and is more closely related to that of the C-terminal amphipathic tail of the Atlastin protein.
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Affiliation(s)
- Frédéric Daste
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Cécile Sauvanet
- Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France
| | - Andrej Bavdek
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - James Baye
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Fabienne Pierre
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France.,Centre de Psychiatrie et Neurosciences, INSERM UMR 894, Sorbonne Paris Cité, Université Paris Descartes, Paris, France
| | - Rémi Le Borgne
- Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Claudine David
- Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France
| | - Manuel Rojo
- Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France
| | - Patrick Fuchs
- Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - David Tareste
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France .,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France.,Centre de Psychiatrie et Neurosciences, INSERM UMR 894, Sorbonne Paris Cité, Université Paris Descartes, Paris, France
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27
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Munc18a clusters SNARE-bearing liposomes prior to trans-SNARE zippering. Biochem J 2017; 474:3339-3354. [PMID: 28827281 DOI: 10.1042/bcj20170494] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 08/16/2017] [Accepted: 08/17/2017] [Indexed: 12/16/2022]
Abstract
Sec1-Munc18 (SM) proteins co-operate with SNAREs {SNAP [soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein] receptors} to mediate membrane fusion in eukaryotic cells. Studies of Munc18a/Munc18-1/Stxbp1 in neurotransmission suggest that SM proteins accelerate fusion kinetics primarily by activating the partially zippered trans-SNARE complex. However, accumulating evidence has argued for additional roles for SM proteins in earlier steps in the fusion cascade. Here, we investigate the function of Munc18a in reconstituted exocytic reactions mediated by neuronal and non-neuronal SNAREs. We show that Munc18a plays a direct role in promoting proteoliposome clustering, underlying vesicle docking during exocytosis. In the three different fusion reactions examined, Munc18a-dependent clustering requires an intact N-terminal peptide (N-peptide) motif in syntaxin that mediates the binary interaction between syntaxin and Munc18a. Importantly, clustering is preserved under inhibitory conditions that abolish both trans-SNARE complex formation and lipid mixing, indicating that Munc18a promotes membrane clustering in a step that is independent of trans-SNARE zippering and activation.
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28
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Oshima A, Sumitomo K. Vesicle fusion with bilayer lipid membrane controlled by electrostatic interaction. Biochem Biophys Rep 2017; 11:58-63. [PMID: 28955768 PMCID: PMC5614691 DOI: 10.1016/j.bbrep.2017.06.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 05/16/2017] [Accepted: 06/16/2017] [Indexed: 11/07/2022] Open
Abstract
The fusion of proteoliposomes is a promising approach for incorporating membrane proteins in artificial lipid membranes. In this study, we employed an electrostatic interaction between vesicles and supported bilayer lipid membranes (s-BLMs) to control the fusion process. We combined large unilamellar vesicles (LUVs) containing anionic lipids, which we used instead of proteoliposomes, and s-BLMs containing cationic lipids to control electrostatic interaction. Anionic LUVs were never adsorbed or ruptured on the SiO2 substrate with a slight negative charge, and selectively fused with cationic s-BLMs. The LUVs can be fused effectively to the target position. Furthermore, as the vesicle fusion proceeds and some of the positive charges are neutralized, the attractive interaction weakens and finally the vesicle fusion saturates. In other words, we can control the number of LUVs fused with s-BLMs by controlling the concentration of the cationic lipids in the s-BLMs. The fluidity of the s-BLMs after vesicle fusion was confirmed to be sufficiently high. This indicates that the LUVs attached to the s-BLMs were almost completely fused, and there were few intermediate state vesicles in the fusion process. We could control the position and amount of vesicle fusion with the s-BLMs by employing an electrostatic interaction.
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Affiliation(s)
- Azusa Oshima
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
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29
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Rehman A, Hu SH, Tnimov Z, Whitten AE, King GJ, Jarrott RJ, Norwood SJ, Alexandrov K, Collins BM, Christie MP, Martin JL. The nature of the Syntaxin4 C-terminus affects Munc18c-supported SNARE assembly. PLoS One 2017; 12:e0183366. [PMID: 28841669 PMCID: PMC5571939 DOI: 10.1371/journal.pone.0183366] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 08/02/2017] [Indexed: 11/18/2022] Open
Abstract
Vesicular transport of cellular cargo requires targeted membrane fusion and formation of a SNARE protein complex that draws the two apposing fusing membranes together. Insulin-regulated delivery and fusion of glucose transporter-4 storage vesicles at the cell surface is dependent on two key proteins: the SNARE integral membrane protein Syntaxin4 (Sx4) and the soluble regulatory protein Munc18c. Many reported in vitro studies of Munc18c:Sx4 interactions and of SNARE complex formation have used soluble Sx4 constructs lacking the native transmembrane domain. As a consequence, the importance of the Sx4 C-terminal anchor remains poorly understood. Here we show that soluble C-terminally truncated Sx4 dissociates more rapidly from Munc18c than Sx4 where the C-terminal transmembrane domain is replaced with a T4-lysozyme fusion. We also show that Munc18c appears to inhibit SNARE complex formation when soluble C-terminally truncated Sx4 is used but does not inhibit SNARE complex formation when Sx4 is C-terminally anchored (by a C-terminal His-tag bound to resin, by a C-terminal T4L fusion or by the native C-terminal transmembrane domain in detergent micelles). We conclude that the C-terminus of Sx4 is critical for its interaction with Munc18c, and that the reported inhibitory role of Munc18c may be an artifact of experimental design. These results support the notion that a primary role of Munc18c is to support SNARE complex formation and membrane fusion.
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Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Zakir Tnimov
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Andrew E. Whitten
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Gordon J. King
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Russell J. Jarrott
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Suzanne J. Norwood
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Kirill Alexandrov
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Brett M. Collins
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Michelle P. Christie
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
- * E-mail: (MPC); (JLM)
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
- * E-mail: (MPC); (JLM)
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Nishigami M, Mori T, Tomita M, Takiguchi K, Tsumoto K. Membrane fusion between baculovirus budded virus-enveloped particles and giant liposomes generated using a droplet-transfer method for the incorporation of recombinant membrane proteins. Colloids Surf B Biointerfaces 2017; 155:248-256. [PMID: 28432958 DOI: 10.1016/j.colsurfb.2017.04.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2016] [Revised: 03/10/2017] [Accepted: 04/04/2017] [Indexed: 10/19/2022]
Abstract
Giant proteoliposomes are generally useful as artificial cell membranes in biochemical and biophysical studies, and various procedures for their preparation have been reported. We present here a novel preparation technique that involves the combination of i) cell-sized lipid vesicles (giant unilamellar vesicles, GUVs) that are generated using the droplet-transfer method, where lipid monolayer-coated water-in-oil microemulsion droplets interact with oil/water interfaces to form enclosed bilayer vesicles, and ii) budded viruses (BVs) of baculovirus (Autographa californica nucleopolyhedrovirus) that express recombinant transmembrane proteins on their envelopes. GP64, a fusogenic glycoprotein on viral envelopes, is activated by weak acids and is thought to cause membrane fusion with liposomes. Using confocal laser scanning microscopy (CLSM), we observed that the single giant liposomes fused with octadecyl rhodamine B chloride (R18)-labeled wild-type BV envelopes with moderate leakage of entrapped soluble compounds (calcein), and the fusion profile depended on the pH of the exterior solution: membrane fusion occurred at pH ∼4-5. We further demonstrated that recombinant transmembrane proteins, a red fluorescent protein (RFP)-tagged GPCR (corticotropin-releasing hormone receptor 1, CRHR1) and envelope protein GP64 could be partly incorporated into membranes of the individual giant liposomes with a reduction of the pH value, though there were also some immobile fluorescent spots observed on their circumferences. This combination may be useful for preparing giant proteoliposomes containing the desired membranes and inner phases.
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Affiliation(s)
- Misako Nishigami
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan
| | - Takaaki Mori
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan
| | - Masahiro Tomita
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan
| | - Kingo Takiguchi
- Division of Biological Science, Graduate School of Science, Nagoya University Furo-cho, Chikusa, Nagoya 464-8602, Japan
| | - Kanta Tsumoto
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan.
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Witkowska A, Jahn R. Rapid SNARE-Mediated Fusion of Liposomes and Chromaffin Granules with Giant Unilamellar Vesicles. Biophys J 2017; 113:1251-1259. [PMID: 28400045 PMCID: PMC5607038 DOI: 10.1016/j.bpj.2017.03.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 03/12/2017] [Accepted: 03/13/2017] [Indexed: 11/03/2022] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins are the main catalysts for membrane fusion in the secretory pathway of eukaryotic cells. In vitro, SNAREs are sufficient to mediate effective fusion of both native and artificial membranes. Here we have established, to our knowledge, a new platform for monitoring SNARE-mediated docking and fusion between giant unilamellar vesicles (GUVs) and smaller liposomes or purified secretory granules with high temporal and spatial resolution. Analysis of fusion is restricted to the free-standing part of the GUV-membrane exhibiting low curvature and a lack of surface contact, thus avoiding adhesion-mediated interference with the fusion reaction as in fusion with supported bilayers or surface-immobilized small vesicles. Our results show that liposomes and chromaffin granules fuse with GUVs containing activated SNAREs with only few milliseconds delay between docking and fusion. We conclude that after initial contact in trans, SNAREs alone can complete fusion at a rate close to fast neuronal exocytosis.
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Affiliation(s)
- Agata Witkowska
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; International Max Planck Research School for Molecular Biology at the University of Göttingen, Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
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Heo P, Park JB, Shin YK, Kweon DH. Visualization of SNARE-Mediated Hemifusion between Giant Unilamellar Vesicles Arrested by Myricetin. Front Mol Neurosci 2017; 10:93. [PMID: 28408867 PMCID: PMC5374201 DOI: 10.3389/fnmol.2017.00093] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Accepted: 03/20/2017] [Indexed: 11/13/2022] Open
Abstract
Neurotransmitters are released within a millisecond after Ca2+ arrives at an active zone. However, the vesicle fusion pathway underlying this synchronous release is yet to be understood. At the center of controversy is whether hemifusion, in which outer leaflets are merged while inner leaflets are still separated, is an on-pathway or off-pathway product of Ca2+-triggered exocytosis. Using the single vesicle fusion assay, we recently demonstrated that hemifusion is an on-pathway intermediate that immediately proceeds to full fusion upon Ca2+ triggering. It has been shown that the flavonoid myricetin arrests soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor (SNARE)-mediated vesicle fusion at hemifusion, but that the hemifused vesicles spontaneously convert to full fusion when the myricetin clamp is removed by the enzyme laccase. In the present study, we visualized SNARE-mediated hemifusion between two SNARE-reconstituted giant unilamellar vesicles (GUVs) arrested by myricetin. The large size of the GUVs enabled us to directly image the hemifusion between them. When two merging GUVs were labeled with different fluorescent dyes, GUV pairs showed asymmetric fluorescence intensities depending on the position on the GUV pair consistent with what is expected for hemifusion. The flow of lipids from one vesicle to the other was revealed with fluorescence recovery after photobleaching (FRAP), indicating that the two membranes had hemifused. These results support the hypothesis that hemifusion may be the molecular status that primes Ca2+-triggered millisecond exocytosis. This study represents the first imaging of SNARE-driven hemifusion between GUVs.
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Affiliation(s)
- Paul Heo
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan UniversitySuwon, South Korea
| | - Joon-Bum Park
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan UniversitySuwon, South Korea
| | - Yeon-Kyun Shin
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State UniversityAmes, IA, USA
| | - Dae-Hyuk Kweon
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan UniversitySuwon, South Korea
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Stein H, Spindler S, Bonakdar N, Wang C, Sandoghdar V. Production of Isolated Giant Unilamellar Vesicles under High Salt Concentrations. Front Physiol 2017; 8:63. [PMID: 28243205 PMCID: PMC5303729 DOI: 10.3389/fphys.2017.00063] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 01/23/2017] [Indexed: 12/22/2022] Open
Abstract
The cell membrane forms a dynamic and complex barrier between the living cell and its environment. However, its in vivo studies are difficult because it consists of a high variety of lipids and proteins and is continuously reorganized by the cell. Therefore, membrane model systems with precisely controlled composition are used to investigate fundamental interactions of membrane components under well-defined conditions. Giant unilamellar vesicles (GUVs) offer a powerful model system for the cell membrane, but many previous studies have been performed in unphysiologically low ionic strength solutions which might lead to altered membrane properties, protein stability and lipid-protein interaction. In the present work, we give an overview of the existing methods for GUV production and present our efforts on forming single, free floating vesicles up to several tens of μm in diameter and at high yield in various buffer solutions with physiological ionic strength and pH.
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Affiliation(s)
- Hannah Stein
- Friedrich-Alexander University Erlangen-NurembergErlangen, Germany; Max Planck Institute for the Science of LightErlangen, Germany
| | - Susann Spindler
- Friedrich-Alexander University Erlangen-NurembergErlangen, Germany; Max Planck Institute for the Science of LightErlangen, Germany
| | - Navid Bonakdar
- Max Planck Institute for the Science of Light Erlangen, Germany
| | - Chun Wang
- Max Planck Institute for the Science of Light Erlangen, Germany
| | - Vahid Sandoghdar
- Friedrich-Alexander University Erlangen-NurembergErlangen, Germany; Max Planck Institute for the Science of LightErlangen, Germany
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34
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Stein H, Spindler S, Bonakdar N, Wang C, Sandoghdar V. Production of Isolated Giant Unilamellar Vesicles under High Salt Concentrations. Front Physiol 2017; 8:63. [PMID: 28243205 DOI: 10.3389/fphys.2017.00063/full] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 01/23/2017] [Indexed: 05/27/2023] Open
Abstract
The cell membrane forms a dynamic and complex barrier between the living cell and its environment. However, its in vivo studies are difficult because it consists of a high variety of lipids and proteins and is continuously reorganized by the cell. Therefore, membrane model systems with precisely controlled composition are used to investigate fundamental interactions of membrane components under well-defined conditions. Giant unilamellar vesicles (GUVs) offer a powerful model system for the cell membrane, but many previous studies have been performed in unphysiologically low ionic strength solutions which might lead to altered membrane properties, protein stability and lipid-protein interaction. In the present work, we give an overview of the existing methods for GUV production and present our efforts on forming single, free floating vesicles up to several tens of μm in diameter and at high yield in various buffer solutions with physiological ionic strength and pH.
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Affiliation(s)
- Hannah Stein
- Friedrich-Alexander University Erlangen-NurembergErlangen, Germany; Max Planck Institute for the Science of LightErlangen, Germany
| | - Susann Spindler
- Friedrich-Alexander University Erlangen-NurembergErlangen, Germany; Max Planck Institute for the Science of LightErlangen, Germany
| | - Navid Bonakdar
- Max Planck Institute for the Science of Light Erlangen, Germany
| | - Chun Wang
- Max Planck Institute for the Science of Light Erlangen, Germany
| | - Vahid Sandoghdar
- Friedrich-Alexander University Erlangen-NurembergErlangen, Germany; Max Planck Institute for the Science of LightErlangen, Germany
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35
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FRAP to Characterize Molecular Diffusion and Interaction in Various Membrane Environments. PLoS One 2016; 11:e0158457. [PMID: 27387979 PMCID: PMC4936743 DOI: 10.1371/journal.pone.0158457] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2016] [Accepted: 06/16/2016] [Indexed: 11/19/2022] Open
Abstract
Fluorescence recovery after photobleaching (FRAP) is a standard method used to study the dynamics of lipids and proteins in artificial and cellular membrane systems. The advent of confocal microscopy two decades ago has made quantitative FRAP easily available to most laboratories. Usually, a single bleaching pattern/area is used and the corresponding recovery time is assumed to directly provide a diffusion coefficient, although this is only true in the case of unrestricted Brownian motion. Here, we propose some general guidelines to perform FRAP experiments under a confocal microscope with different bleaching patterns and area, allowing the experimentalist to establish whether the molecules undergo Brownian motion (free diffusion) or whether they have restricted or directed movements. Using in silico simulations of FRAP measurements, we further indicate the data acquisition criteria that have to be verified in order to obtain accurate values for the diffusion coefficient and to be able to distinguish between different diffusive species. Using this approach, we compare the behavior of lipids in three different membrane platforms (supported lipid bilayers, giant liposomes and sponge phases), and we demonstrate that FRAP measurements are consistent with results obtained using other techniques such as Fluorescence Correlation Spectroscopy (FCS) or Single Particle Tracking (SPT). Finally, we apply this method to show that the presence of the synaptic protein Munc18-1 inhibits the interaction between the synaptic vesicle SNARE protein, VAMP2, and its partner from the plasma membrane, Syn1A.
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36
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Park S, Bin NR, Rajah M, Kim B, Chou TC, Kang SYA, Sugita K, Parsaud L, Smith M, Monnier PP, Ikura M, Zhen M, Sugita S. Conformational states of syntaxin-1 govern the necessity of N-peptide binding in exocytosis of PC12 cells and Caenorhabditis elegans. Mol Biol Cell 2015; 27:669-85. [PMID: 26700321 PMCID: PMC4750926 DOI: 10.1091/mbc.e15-09-0638] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 12/18/2015] [Indexed: 11/11/2022] Open
Abstract
Syntaxin-1 is the central SNARE protein for neuronal exocytosis. It interacts with Munc18-1 through its cytoplasmic domains, including the N-terminal peptide (N-peptide). Here we examine the role of the N-peptide binding in two conformational states ("closed" vs. "open") of syntaxin-1 using PC12 cells and Caenorhabditis elegans. We show that expression of "closed" syntaxin-1A carrying N-terminal single point mutations (D3R, L8A) that perturb interaction with the hydrophobic pocket of Munc18-1 rescues impaired secretion in syntaxin-1-depleted PC12 cells and the lethality and lethargy of unc-64 (C. elegans orthologue of syntaxin-1)-null mutants. Conversely, expression of the "open" syntaxin-1A harboring the same mutations fails to rescue the impairments. Biochemically, the L8A mutation alone slightly weakens the binding between "closed" syntaxin-1A and Munc18-1, whereas the same mutation in the "open" syntaxin-1A disrupts it. Our results reveal a striking interplay between the syntaxin-1 N-peptide and the conformational state of the protein. We propose that the N-peptide plays a critical role in intracellular trafficking of syntaxin-1, which is dependent on the conformational state of this protein. Surprisingly, however, the N-peptide binding mode seems dispensable for SNARE-mediated exocytosis per se, as long as the protein is trafficked to the plasma membrane.
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Affiliation(s)
- Seungmee Park
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Na-Ryum Bin
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Maaran Rajah
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Byungjin Kim
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Ting-Chieh Chou
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Soo-Young Ann Kang
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Kyoko Sugita
- Division of Genetics and Development, Krembil Discovery Tower, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Leon Parsaud
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Matthew Smith
- Division of Signaling Biology, MaRS Toronto Medical Discovery Tower, Ontario Cancer Institute, University Health Network, Toronto, ON M5G 1L7, Canada Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 1L7, Canada
| | - Philippe P Monnier
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Division of Genetics and Development, Krembil Discovery Tower, University Health Network, Toronto, ON M5T 2S8, Canada
| | - Mitsuhiko Ikura
- Division of Genetics and Development, Krembil Discovery Tower, University Health Network, Toronto, ON M5T 2S8, Canada Division of Signaling Biology, MaRS Toronto Medical Discovery Tower, Ontario Cancer Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Mei Zhen
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Shuzo Sugita
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
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37
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Shen C, Rathore SS, Yu H, Gulbranson DR, Hua R, Zhang C, Schoppa NE, Shen J. The trans-SNARE-regulating function of Munc18-1 is essential to synaptic exocytosis. Nat Commun 2015; 6:8852. [PMID: 26572858 PMCID: PMC4668942 DOI: 10.1038/ncomms9852] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 10/09/2015] [Indexed: 11/09/2022] Open
Abstract
The fusion of neurotransmitter-filled synaptic vesicles with the plasma membrane requires two classes of molecules-SNAP receptor (SNARE) and Sec1/Munc18 (SM) protein. Reconstitution studies suggest that the SM protein Munc18-1 promotes the zippering of trans-SNARE complexes and accelerates the kinetics of SNARE-dependent membrane fusion. However, the physiological role of this trans-SNARE-regulating function in synaptic exocytosis remains to be established. Here we first demonstrate that two mutations in the vesicle-anchored v-SNARE selectively impair the ability of Munc18-1 to promote trans-SNARE zippering, whereas other known Munc18-1/SNARE-binding modes are unaffected. In cultured neurons, these v-SNARE mutations strongly inhibit spontaneous as well as evoked neurotransmitter release, providing genetic evidence for the trans-SNARE-regulating function of Munc18-1 in synaptic exocytosis. Finally, we show that the trans-SNARE-regulating function of Munc18-1 is compromised by a mutation associated with Ohtahara Syndrome, a severe form of epilepsy.
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Affiliation(s)
- Chong Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Shailendra S Rathore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Daniel R Gulbranson
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Rui Hua
- State Key Laboratory of Membrane Biology, School of Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Chen Zhang
- State Key Laboratory of Membrane Biology, School of Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Nathan E Schoppa
- Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado 80045, USA
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
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38
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Yu H, Rathore SS, Shen C, Liu Y, Ouyang Y, Stowell MH, Shen J. Reconstituting Intracellular Vesicle Fusion Reactions: The Essential Role of Macromolecular Crowding. J Am Chem Soc 2015; 137:12873-83. [PMID: 26431309 DOI: 10.1021/jacs.5b08306] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intracellular vesicle fusion is mediated by SNAREs and Sec1/Munc18 (SM) proteins. Despite intensive efforts, the SNARE-SM mediated vesicle fusion reaction has not been faithfully reconstituted in biochemical assays. Here, we present an unexpected discovery that macromolecular crowding is required for reconstituting the vesicle fusion reaction in vitro. Macromolecular crowding is known to profoundly influence the kinetic and thermodynamic behaviors of macromolecules, but its role in membrane transport processes such as vesicle fusion remains unexplored. We introduced macromolecular crowding agents into reconstituted fusion reactions to mimic the crowded cellular environment. In this crowded assay, SNAREs and SM proteins acted in concert to drive efficient membrane fusion. In uncrowded assays, by contrast, SM proteins failed to associate with the SNAREs and the fusion rate decreased more than 30-fold, close to undetectable levels. The activities of SM proteins were strictly specific to their cognate SNARE isoforms and sensitive to biologically relevant mutations, further supporting that the crowded fusion assay accurately recapitulates the vesicle fusion reaction. Using this crowded fusion assay, we also showed that the SNARE-SM mediated fusion reaction can be modulated by two additional factors: NSF and α-SNAP. These findings suggest that the vesicle fusion machinery likely has been evolutionarily selected to function optimally in the crowded milieu of the cell. Accordingly, macromolecular crowding should constitute an integral element of any reconstituted fusion assay.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Shailendra S Rathore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Chong Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Yinghui Liu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Yan Ouyang
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Michael H Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
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39
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Schwenen LLG, Hubrich R, Milovanovic D, Geil B, Yang J, Kros A, Jahn R, Steinem C. Resolving single membrane fusion events on planar pore-spanning membranes. Sci Rep 2015; 5:12006. [PMID: 26165860 PMCID: PMC4499801 DOI: 10.1038/srep12006] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 06/15/2015] [Indexed: 12/15/2022] Open
Abstract
Even though a number of different in vitro fusion assays have been developed to analyze protein mediated fusion, they still only partially capture the essential features of the in vivo situation. Here we established an in vitro fusion assay that mimics the fluidity and planar geometry of the cellular plasma membrane to be able to monitor fusion of single protein-containing vesicles. As a proof of concept, planar pore-spanning membranes harboring SNARE-proteins were generated on highly ordered functionalized 1.2 μm-sized pore arrays in Si3N4. Full mobility of the membrane components was demonstrated by fluorescence correlation spectroscopy. Fusion was analyzed by two color confocal laser scanning fluorescence microscopy in a time resolved manner allowing to readily distinguish between vesicle docking, intermediate states such as hemifusion and full fusion. The importance of the membrane geometry on the fusion process was highlighted by comparing SNARE-mediated fusion with that of a minimal SNARE fusion mimetic.
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Affiliation(s)
- Lando L G Schwenen
- Institute for Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
| | - Raphael Hubrich
- Institute for Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
| | - Dragomir Milovanovic
- Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Burkhard Geil
- Institute for Physical Chemistry, University of Göttingen, Tammannstr. 6, 37077 Göttingen, Germany
| | - Jian Yang
- Leiden Institute of Chemistry - Supramolecular and Biomaterials Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Alexander Kros
- Leiden Institute of Chemistry - Supramolecular and Biomaterials Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Reinhard Jahn
- Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Claudia Steinem
- Institute for Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
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40
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Motta I, Gohlke A, Adrien V, Li F, Gardavot H, Rothman JE, Pincet F. Formation of Giant Unilamellar Proteo-Liposomes by Osmotic Shock. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:7091-7099. [PMID: 26038815 PMCID: PMC4950989 DOI: 10.1021/acs.langmuir.5b01173] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Giant unilamellar vesicles (GUVs), composed of a phospholipid bilayer, are often used as a model system for cell membranes. However, the study of proteo-membrane interactions in this system is limited as the incorporation of integral and lipid-anchored proteins into GUVs remains challenging. Here, we present a simple generic method to incorporate proteins into GUVs. The basic principle is to break proteo-liposomes with an osmotic shock. They subsequently reseal into larger vesicles which, if necessary, can endure the same to obtain even larger proteo-GUVs. This process does not require specific lipids or reagents, works under physiological conditions with high concentrations of protein, the proteins remains functional after incorporation. The resulting proteo-GUVs can be micromanipulated. Moreover, our protocol is valid for a wide range of protein substrates. We have successfully reconstituted three structurally different proteins, two trans-membrane proteins (TolC and the neuronal t-SNARE), and one lipid-anchored peripheral protein (GABARAP-Like 1 (GL1)). In each case, we verified that the protein remains active after incorporation and in its correctly folded state. We also measured their mobility by performing diffusion measurements via fluorescence recovery after photobleaching (FRAP) experiments on micromanipulated single GUVs. The diffusion coefficients are in agreement with previous data.
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Affiliation(s)
- Isabelle Motta
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
| | - Andrea Gohlke
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - Vladimir Adrien
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
- Laboratoire de Cristallographie et RMN Biologiques, Université Paris Descartes, CNRS, UMR 8015, Paris, France
| | - Feng Li
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - Hélène Gardavot
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
| | - James E. Rothman
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - Frederic Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
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Kiessling V, Liang B, Tamm LK. Reconstituting SNARE-mediated membrane fusion at the single liposome level. Methods Cell Biol 2015; 128:339-63. [PMID: 25997356 DOI: 10.1016/bs.mcb.2015.02.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Successful reconstitutions of SNARE-mediated intracellular membrane fusion have been achieved in bulk fusion assays since 1998 and in single liposome fusion assays since 2004. Especially in neuronal presynaptic SNARE-mediated exocytosis, fusion is controlled by numerous accessory proteins, of which some functions have also been reconstituted in vitro. The development of and results obtained with two fundamentally different single liposome fusion assays, namely liposome-to-supported membrane and liposome-to-liposome, are reviewed. Both assays distinguish between liposome docking and fusion steps of the overall fusion reaction and both assays are capable of resolving hemi-and full-fusion intermediates and end states. They have opened new windows for elucidating the mechanisms of these fundamentally important cellular reactions with unprecedented time and molecular resolution. Although many of the molecular actors in this process have been discovered, we have only scratched the surface of looking at their fascinating plays, interactions, and choreographies that lead to vesicle traffic as well as neurotransmitter and hormone release in the cell.
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Affiliation(s)
- Volker Kiessling
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Binyong Liang
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
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42
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Bin NR, Jung CH, Kim B, Chandrasegram P, Turlova E, Zhu D, Gaisano HY, Sun HS, Sugita S. Chaperoning of closed syntaxin-3 through Lys46 and Glu59 in domain 1 of Munc18 proteins is indispensable for mast cell exocytosis. J Cell Sci 2015; 128:1946-60. [PMID: 25795302 DOI: 10.1242/jcs.165662] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 03/16/2015] [Indexed: 11/20/2022] Open
Abstract
Understanding how Munc18 proteins govern exocytosis is crucial because mutations of this protein cause severe secretion deficits in neuronal and immune cells. Munc18-2 has indispensable roles in the degranulation of mast cell, partly by binding and chaperoning a subset of syntaxin isoforms. However, the key syntaxin that, crucially, participates in the degranulation – whose levels and intracellular localization are regulated by Munc18-2 – remains unknown. Here, we demonstrate that double knockdown of Munc18-1 and Munc-2 in mast cells results in greatly reduced degranulation accompanied with strikingly compromised expression levels and localization of syntaxin-3. This phenotype is fully rescued by wild-type Munc18 proteins but not by the K46E, E59K and K46E/E59K mutants of Munc-18 domain 1, each of which exhibits completely abolished binding to 'closed' syntaxin-3. Furthermore, knockdown of syntaxin-3 strongly impairs degranulation. Collectively, our data argue that residues Lys46 and Glu59 of Munc18 proteins are indispensable for mediating the interaction between Munc18 and closed syntaxin-3, which is essential for degranulation by chaperoning syntaxin-3. Our results also indicate that the functional contribution of these residues differs between immune cell degranulation and neuronal secretion.
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Affiliation(s)
- Na-Ryum Bin
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Chang Hun Jung
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Byungjin Kim
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada
| | - Prashanth Chandrasegram
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada
| | - Ekaterina Turlova
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Dan Zhu
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Herbert Y Gaisano
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Hong-Shuo Sun
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada Department of Surgery, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Shuzo Sugita
- Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Krembil Discovery Tower, Toronto, ON M5T 2S8, Canada Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
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43
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Rehman A, Archbold JK, Hu SH, Norwood SJ, Collins BM, Martin JL. Reconciling the regulatory role of Munc18 proteins in SNARE-complex assembly. IUCRJ 2014; 1:505-513. [PMID: 25485130 PMCID: PMC4224468 DOI: 10.1107/s2052252514020727] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/15/2014] [Indexed: 06/04/2023]
Abstract
Membrane fusion is essential for human health, playing a vital role in processes as diverse as neurotransmission and blood glucose control. Two protein families are key: (1) the Sec1p/Munc18 (SM) and (2) the soluble N-ethylmaleimide-sensitive attachment protein receptor (SNARE) proteins. Whilst the essential nature of these proteins is irrefutable, their exact regulatory roles in membrane fusion remain controversial. In particular, whether SM proteins promote and/or inhibit the SNARE-complex formation required for membrane fusion is not resolved. Crystal structures of SM proteins alone and in complex with their cognate SNARE proteins have provided some insight, however, these structures lack the transmembrane spanning regions of the SNARE proteins and may not accurately reflect the native state. Here, we review the literature surrounding the regulatory role of mammalian Munc18 SM proteins required for exocytosis in eukaryotes. Our analysis suggests that the conflicting roles reported for these SM proteins may reflect differences in experimental design. SNARE proteins appear to require C-terminal immobilization or anchoring, for example through a transmembrane domain, to form a functional fusion complex in the presence of Munc18 proteins.
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Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Julia K. Archbold
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Suzanne J. Norwood
- Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Brett M. Collins
- Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
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44
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Han GA, Park S, Bin NR, Jung CH, Kim B, Chandrasegaram P, Matsuda M, Riadi I, Han L, Sugita S. A pivotal role for pro-335 in balancing the dual functions of Munc18-1 domain-3a in regulated exocytosis. J Biol Chem 2014; 289:33617-28. [PMID: 25326390 DOI: 10.1074/jbc.m114.584805] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Munc18-1 plays essential dual roles in exocytosis: (i) stabilizing and trafficking the central SNARE protein, syntaxin-1 (i.e. chaperoning function), by its domain-1; and (ii) priming/stimulating exocytosis by its domain-3a. Here, we examine whether or not domain-3a also plays a significant role in the chaperoning of syntaxin-1 and, if so, how these dual functions of domain-3a are regulated. We demonstrate that introduction of quintuple mutations (K332E/K333E/P335A/Q336A/Y337L) in domain-3a of Munc18-1 abolishes its ability to bind syntaxin-1 and fails to rescue the level and trafficking of syntaxin-1 as well as to restore exocytosis in Munc18-1/2 double knockdown cells. By contrast, a quadruple mutant (K332E/K333E/Q336A/Y337L) sparing the Pro-335 residue retains all of these capabilities. A single point mutant of P335A reduces the ability to bind syntaxin-1 and rescue syntaxin-1 levels. Nonetheless, it surprisingly outperforms the wild type in the rescue of exocytosis. However, when additional mutations in the neighboring residues are combined with P335A mutation (K332E/K333E/P335A, P335A/Q336A/Y337L), the ability of the Munc18-1 variants to chaperone syntaxin-1 and to rescue exocytosis is strongly impaired. Our results indicate that residues from Lys-332 to Tyr-337 of domain-3a are intimately tied to the chaperoning function of Munc18-1. We also propose that Pro-335 plays a pivotal role in regulating the balance between the dual functions of domain-3a. The hinged conformation of the α-helix containing Pro-335 promotes the syntaxin-1 chaperoning function, whereas the P335A mutation promotes its priming function by facilitating the α-helix to adopt an extended conformation.
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Affiliation(s)
- Gayoung Anna Han
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Seungmee Park
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Na-Ryum Bin
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Chang Hun Jung
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Byungjin Kim
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Prashanth Chandrasegaram
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Maiko Matsuda
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Indira Riadi
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and
| | - Liping Han
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Shuzo Sugita
- From the Division of Fundamental Neurobiology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and the Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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45
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Petkovic M, Jemaiel A, Daste F, Specht CG, Izeddin I, Vorkel D, Verbavatz JM, Darzacq X, Triller A, Pfenninger KH, Tareste D, Jackson CL, Galli T. The SNARE Sec22b has a non-fusogenic function in plasma membrane expansion. Nat Cell Biol 2014; 16:434-44. [PMID: 24705552 DOI: 10.1038/ncb2937] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Accepted: 02/20/2014] [Indexed: 12/13/2022]
Abstract
Development of the nervous system requires extensive axonal and dendritic growth during which neurons massively increase their surface area. Here we report that the endoplasmic reticulum (ER)-resident SNARE Sec22b has a conserved non-fusogenic function in plasma membrane expansion. Sec22b is closely apposed to the plasma membrane SNARE syntaxin1. Sec22b forms a trans-SNARE complex with syntaxin1 that does not include SNAP23/25/29, and does not mediate fusion. Insertion of a long rigid linker between the SNARE and transmembrane domains of Sec22b extends the distance between the ER and plasma membrane, and impairs neurite growth but not the secretion of VSV-G. In yeast, Sec22 interacts with lipid transfer proteins, and inhibition of Sec22 leads to defects in lipid metabolism at contact sites between the ER and plasma membrane. These results suggest that close apposition of the ER and plasma membrane mediated by Sec22 and plasma membrane syntaxins generates a non-fusogenic SNARE bridge contributing to plasma membrane expansion, probably through non-vesicular lipid transfer.
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Affiliation(s)
- Maja Petkovic
- 1] INSERM, U950, F-75013 Paris, France [2] Université Paris Diderot, Sorbonne Paris Cité, ERL U950, F-75013 Paris, France [3] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France [4] Ecole des Neurosciences de Paris (ENP), F-75006 Paris, France [5]
| | - Aymen Jemaiel
- 1] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France [2] Membrane Dynamics and Intracellular Trafficking, Institute Jacques Monod, F-75013 Paris, France [3]
| | - Frédéric Daste
- 1] INSERM, U950, F-75013 Paris, France [2] Université Paris Diderot, Sorbonne Paris Cité, ERL U950, F-75013 Paris, France [3] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France [4] Ecole Doctorale Frontières du Vivant (FdV) - Programme Bettencourt, Université Paris Descartes, Sorbonne Paris Cité, F-75004 Paris, France [5]
| | - Christian G Specht
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Biologie Cellulaire de la Synapse, INSERM U1024, CNRS UMR8197, F-75005 Paris, France
| | - Ignacio Izeddin
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Functional Imaging of Transcription, INSERM U1024, CNRS UMR8197, F-75005 Paris, France
| | - Daniela Vorkel
- Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany
| | - Jean-Marc Verbavatz
- 1] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France [2] Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany
| | - Xavier Darzacq
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Functional Imaging of Transcription, INSERM U1024, CNRS UMR8197, F-75005 Paris, France
| | - Antoine Triller
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Biologie Cellulaire de la Synapse, INSERM U1024, CNRS UMR8197, F-75005 Paris, France
| | - Karl H Pfenninger
- Linda Crnic Institute for Down Syndrome and Department of Pediatrics, University Colorado School of Medicine, Aurora, Colorado 80045, USA
| | - David Tareste
- 1] INSERM, U950, F-75013 Paris, France [2] Université Paris Diderot, Sorbonne Paris Cité, ERL U950, F-75013 Paris, France [3] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France
| | - Catherine L Jackson
- 1] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France [2] Membrane Dynamics and Intracellular Trafficking, Institute Jacques Monod, F-75013 Paris, France
| | - Thierry Galli
- 1] INSERM, U950, F-75013 Paris, France [2] Université Paris Diderot, Sorbonne Paris Cité, ERL U950, F-75013 Paris, France [3] CNRS, UMR 7592, Institut Jacques Monod, F-75013 Paris, France
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46
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Parisotto D, Pfau M, Scheutzow A, Wild K, Mayer MP, Malsam J, Sinning I, Söllner TH. An extended helical conformation in domain 3a of Munc18-1 provides a template for SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex assembly. J Biol Chem 2014; 289:9639-50. [PMID: 24532794 DOI: 10.1074/jbc.m113.514273] [Citation(s) in RCA: 94] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Munc18-1, a SEC1/Munc18 protein and key regulatory protein in synaptic transmission, can either promote or inhibit SNARE complex assembly. Although the binary inhibitory interaction between Munc18-1 and closed syntaxin 1 is well described, the mechanism of how Munc18-1 stimulates membrane fusion remains elusive. Using a reconstituted assay that resolves vesicle docking, priming, clamping, and fusion during synaptic exocytosis, we show that helix 12 in domain 3a of Munc18-1 stimulates SNAREpin assembly and membrane fusion. A single point mutation (L348R) within helix 12 selectively abolishes VAMP2 binding and the stimulatory function of Munc18-1 in membrane fusion. In contrast, targeting a natural switch site (P335A) at the start of helix 12, which can result in an extended α-helical conformation, further accelerates lipid-mixing. Together with structural modeling, the data suggest that helix 12 provides a folding template for VAMP2, accelerating SNAREpin assembly and membrane fusion. Analogous SEC1/Munc18-SNARE interactions at other transport steps may provide a general mechanism to drive lipid bilayer merger. At the neuronal synapse, Munc18-1 may convert docked synaptic vesicles into a readily releasable pool.
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Affiliation(s)
- Daniel Parisotto
- From the Heidelberg University Biochemistry Center (BZH), Im Neuenheimer Feld 328, 69120 Heidelberg, Germany and
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47
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Hatayama H, Toyota T, Hayashi H, Nomoto T, Fujinami M. Application of a novel near infrared-fluorescence giant vesicle- and polymerasome-based tissue marker for endoscopic and laparoscopic navigation. ANAL SCI 2014; 30:225-30. [PMID: 24521908 DOI: 10.2116/analsci.30.225] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In this study, we describe the development of a novel tissue marker that can be injected from within the digestive tract by using an endoscopic instrument, and visualized using near-infrared (NIR) fluorescence imaging. The marker was prepared in three steps, (i) mixing NIR-fluorescent indocyanine green (ICG) with giant vesicles (GVs) of lecithin, (ii) suspending the ICG-containing giant vesicles (ICG-GV) in an oil phase dissolving polyglycerol-polyricinoleate (PGPR), and (iii) centrifugation of the suspension layered on a buffered solution to obtain a giant polymer vesicle (polymerasome) containing ICG-GV. We injected the tissue marker into the inner gastric surface of an anesthetized pig using an endoscopic syringe, and observed the injection site using a fluorescence laparoscopic camera. The diameter of the spot blur was approximately 2 cm over a 5-h period, demonstrating the utility of this procedure as a tissue marker for tumor marking, and suggesting its potential for assisting navigation during surgical procedures.
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Affiliation(s)
- Hirosuke Hatayama
- Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University
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48
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Secretagogue stimulation of neurosecretory cells elicits filopodial extensions uncovering new functional release sites. J Neurosci 2014; 33:19143-53. [PMID: 24305811 DOI: 10.1523/jneurosci.2634-13.2013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Regulated exocytosis in neurosecretory cells relies on the timely fusion of secretory granules (SGs) with the plasma membrane. Secretagogue stimulation leads to an enlargement of the cell footprint (surface area in contact with the coverslip), an effect previously attributed to exocytic fusion of SGs with the plasma membrane. Using total internal reflection fluorescence microscopy, we reveal the formation of filopodia-like structures in bovine chromaffin and PC12 cells driving the footprint expansion, suggesting the involvement of cortical actin network remodeling in this process. Using exocytosis-incompetent PC12 cells, we demonstrate that footprint enlargement is largely independent of SG fusion, suggesting that vesicular exocytic fusion plays a relatively minor role in filopodial expansion. The footprint periphery, including filopodia, undergoes extensive F-actin remodeling, an effect abolished by the actomyosin inhibitors cytochalasin D and blebbistatin. Imaging of both Lifeact-GFP and the SG marker protein neuropeptide Y-mCherry reveals that SGs actively translocate along newly forming actin tracks before undergoing fusion. Together, these data demonstrate that neurosecretory cells regulate the number of SGs undergoing exocytosis during sustained stimulation by controlling vesicular mobilization and translocation to the plasma membrane through actin remodeling. Such remodeling facilitates the de novo formation of fusion sites.
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49
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Martin S, Tomatis VM, Papadopulos A, Christie MP, Malintan NT, Gormal RS, Sugita S, Martin JL, Collins BM, Meunier FA. The Munc18-1 domain 3a loop is essential for neuroexocytosis but not for syntaxin-1A transport to the plasma membrane. J Cell Sci 2013; 126:2353-60. [PMID: 23761923 DOI: 10.1242/jcs.126813] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Munc18-1 plays a dual role in transporting syntaxin-1A (Sx1a) to the plasma membrane and regulating SNARE-mediated membrane fusion. As impairment of either function leads to a common exocytic defect, assigning specific roles for various Munc18-1 domains has proved difficult. Structural analyses predict that a loop region in Munc18-1 domain 3a could catalyse the conversion of Sx1a from a 'closed', fusion-incompetent to an 'open', fusion-competent conformation. As this conversion occurs at the plasma membrane, mutations in this loop could potentially separate the chaperone and exocytic functions of Munc18-1. Expression of a Munc18-1 deletion mutant lacking 17 residues of the domain 3a loop (Munc18-1(Δ317-333)) in PC12 cells deficient in endogenous Munc18 (DKD-PC12 cells) fully rescued transport of Sx1a to the plasma membrane, but not exocytic secretory granule fusion. In vitro binding of Munc18-1(Δ317-333) to Sx1a was indistinguishable from that of full-length Munc18-1, consistent with the critical role of the closed conformation in Sx1a transport. However, in DKD-PC12 cells, Munc18-1(Δ317-333) binding to Sx1a was greatly reduced compared to that of full-length Munc18-1, suggesting that closed conformation binding contributes little to the overall interaction at the cell surface. Furthermore, we found that Munc18-1(Δ317-333) could bind SNARE complexes in vitro, suggesting that additional regulatory factors underpin the exocytic function of Munc18-1 in vivo. Together, these results point to a defined role for Munc18-1 in facilitating exocytosis linked to the loop region of domain 3a that is clearly distinct from its function in Sx1a transport.
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Affiliation(s)
- Sally Martin
- Queensland Brain Institute, The University of Queensland, Brisbane QLD 4072, Australia
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50
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Comparative studies of Munc18c and Munc18-1 reveal conserved and divergent mechanisms of Sec1/Munc18 proteins. Proc Natl Acad Sci U S A 2013; 110:E3271-80. [PMID: 23918365 DOI: 10.1073/pnas.1311232110] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Sec1/Munc18 (SM) family proteins are essential for every vesicle fusion pathway. The best-characterized SM protein is the synaptic factor Munc18-1, but it remains unclear whether its functions represent conserved mechanisms of SM proteins or specialized activities in neurotransmitter release. To address this question, we dissected Munc18c, a functionally distinct SM protein involved in nonsynaptic exocytic pathways. We discovered that Munc18c binds to the trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex and strongly accelerates the fusion rate. Further analysis suggests that Munc18c recognizes both vesicle-rooted SNARE and target membrane-associated SNAREs, and promotes trans-SNARE zippering at the postdocking stage of the fusion reaction. The stimulation of fusion by Munc18c is specific to its cognate SNARE isoforms. Because Munc18-1 regulates fusion in a similar manner, we conclude that one conserved function of SM proteins is to bind their cognate trans-SNARE complexes and accelerate fusion kinetics. Munc18c also binds syntaxin-4 monomer but does not block target membrane-associated SNARE assembly, in agreement with our observation that six- to eightfold increases in Munc18c expression do not inhibit insulin-stimulated glucose uptake in adipocytes. Thus, the inhibitory "closed" syntaxin binding mode demonstrated for Munc18-1 is not conserved in Munc18c. Unexpectedly, we found that Munc18c recognizes the N-terminal region of the vesicle-rooted SNARE, whereas Munc18-1 requires the C-terminal sequences, suggesting that the architecture of the SNARE/SM complex likely differs across fusion pathways. Together, these comparative studies of two distinct SM proteins reveal conserved as well as divergent mechanisms of SM family proteins in intracellular vesicle fusion.
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