Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Review Article
  • Published:

Snares and munc18 in synaptic vesicle fusion

Key Points

  • Neurotransmitter release is an exquisitely regulated process in which an influx of Ca2+ leads to exocytosis of synaptic vesicles. Homologues of some of the proteins that are involved also mediate membrane traffic in other compartments.

  • SNARE (SNAP receptor) proteins are among the most studied of these proteins. It has been proposed that SNAREs on the two membranes form a core complex that brings them together and leads to fusion. However, there is debate about the exact role of the SNAREs, and some evidence indicates that SNAREs might act as cofactors or catalysts for fusion rather than mediating it directly.

  • SNAREs are classified as v- and t-SNAREs (present on vesicle and target membranes, respectively) or Q- and R-SNAREs (contributing glutamine and arginine, respectively, to a central polar layer of the core complex). The core complex consists of four SNARE motifs, three Q-SNAREs and one R-SNARE, and is disassembled after fusion by the ATPase activity of NSF (N-ethylmaleimide-sensitive fusion protein). NSF binds to the core complex through SNAPs (soluble NSF-attachment proteins).

  • The SNARE hypothesis proposes that specific recognition between t-SNAREs and v-SNAREs directs vesicle targeting, but there is evidence for promiscuity in SNARE–SNARE interactions.

  • The neuronal SNARE protein syntaxin 1 also has an amino-terminal region that allows it to form a tight complex with the neuronal SM (Sec1/Munc18 homologue) protein Munc18-1. Isolated syntaxin binds to Munc18-1 in a closed conformation, but it must change to an open conformation before forming part of a core complex.

  • SM proteins are essential for membrane fusion, although there is evidence that Munc18-1 inhibits formation of the core complex by binding to the closed conformation of syntaxin 1. The function of this interaction is unclear. Two proteins (UNC-13/Munc13 and RIM) have been proposed to mediate the dissociation of Munc18-1 from syntaxin 1.

  • Other SM and SNARE proteins appear to have different modes of binding, and the syntaxin-1–Munc18-1 interaction might not be typical.

  • Complexins are another family of proteins that bind to neuronal SNAREs. They bind to the SNARE core complex and appear to be involved in the Ca2+-dependent step of neurotransmitter exocytosis, perhaps by stabilizing a primed state with a fully assembled core complex.

  • Important questions that remain unanswered include the function of Munc18-1, the exact involvement of SNAREs in membrane fusion and the structural organization of the active zone.

Abstract

The release of neurotransmitters by Ca2+-triggered synaptic vesicle exocytosis is an exquisitely regulated process that is fundamental for interneuronal communication. This process involves several steps and is controlled by a protein machinery that must prevent release before Ca2+ entry into presynaptic terminals, and yet must rapidly induce release on Ca2+ influx. Extensive studies of the components of this machinery have indicated that SNAREs and Munc18-1 are central proteins for membrane fusion during exocytosis. An increasing amount of information derived from a convergence of structural, physiological and genetic studies is providing important insights into the mechanism of neurotransmitter release.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Cycle of assembly and disassembly of the SNARE complex in synaptic vesicle exocytosis.
Figure 2: Model of the neuronal SNAREs assembled into the core complex.
Figure 3: Crystal structures of NSF and Sec17.
Figure 4: Structure of the syntaxin-1/Munc18-1 complex102.
Figure 5: Different modes of coupling between syntaxins and SM proteins.
Figure 6: Three-dimensional structure of the complexin–SNARE complex156.
Figure 7: Model of complexin function.

Similar content being viewed by others

References

  1. Sabatini, B. L. & Regehr, W. G. Timing of synaptic transmission. Annu. Rev. Physiol. 61, 521–542 (1999).

    CAS  PubMed  Google Scholar 

  2. Sudhof, T. C. The synaptic vesicle cycle: a cascade of protein–protein interactions. Nature 375, 645–653 (1995).

    CAS  PubMed  Google Scholar 

  3. Bennett, M. K. & Scheller, R. H. The molecular machinery for secretion is conserved from yeast to neurons. Proc. Natl Acad. Sci. USA 90, 2559–2563 (1993).

    CAS  PubMed  PubMed Central  Google Scholar 

  4. Ferro-Novick, S. & Jahn, R. Vesicle fusion from yeast to man. Nature 370, 191–193 (1994).

    CAS  PubMed  Google Scholar 

  5. McNew, J. A. et al. Compartmental specificity of cellular membrane fusion encoded in SNARE proteins. Nature 407, 153–159 (2000).

    CAS  PubMed  Google Scholar 

  6. Hanson, P. I., Roth, R., Morisaki, H., Jahn, R. & Heuser, J. E. Structure and conformational changes in NSF and its membrane receptor complexes visualized by quick-freeze/deep-etch electron microscopy. Cell 90, 523–535 (1997).Beautiful EM experiments showed that the SNARE motifs of synaptobrevin and syntaxin interact in a parallel fashion, leading to the hypothesis that core-complex assembly might directly cause membrane fusion.

    CAS  PubMed  Google Scholar 

  7. Lin, R. C. & Scheller, R. H. Structural organization of the synaptic exocytosis core complex. Neuron 19, 1087–1094 (1997).

    CAS  PubMed  Google Scholar 

  8. Weber, T. et al. SNAREpins: minimal machinery for membrane fusion. Cell 92, 759–772 (1998).In these reconstitution studies of SNAREs incorporated into liposomes, experimental evidence was provided to support the hypothesis that core-complex formation might cause membrane fusion.

    CAS  PubMed  Google Scholar 

  9. Jahn, R. & Sudhof, T. C. Membrane fusion and exocytosis. Annu. Rev. Biochem. 68, 863–911 (1999).

    CAS  PubMed  Google Scholar 

  10. Ungermann, C., Sato, K. & Wickner, W. Defining the functions of trans-SNARE pairs. Nature 396, 543–548 (1998).

    CAS  PubMed  Google Scholar 

  11. Tahara, M. et al. Calcium can disrupt the SNARE protein complex on sea urchin egg secretory vesicles without irreversibly blocking fusion. J. Biol. Chem. 273, 33667–33673 (1998).

    CAS  PubMed  Google Scholar 

  12. Lonart, G. & Sudhof, T. C. Assembly of SNARE core complexes prior to neurotransmitter release sets the readily releasable pool of synaptic vesicles. J. Biol. Chem. 275, 27703–27707 (2000).

    CAS  PubMed  Google Scholar 

  13. Schoch, S. et al. SNARE function analyzed in synaptobrevin/VAMP knockout mice. Science 294, 1117–1122 (2001).Shows that knockout of synaptobrevin affects Ca2+-triggered fusion more than Ca2+-independent fusion.

    CAS  PubMed  Google Scholar 

  14. Peters, C. et al. Trans-complex formation by proteolipid channels in the terminal phase of membrane fusion. Nature 409, 581–588 (2001).

    CAS  PubMed  Google Scholar 

  15. Carr, C. M., Grote, E., Munson, M., Hughson, F. M. & Novick, P. J. Sec1p binds to SNARE complexes and concentrates at sites of secretion. J. Cell Biol. 146, 333–344 (1999).In this study, yeast Sec1 was shown to bind to core complexes that contain the yeast plasma-membrane syntaxin Sso1, rather than to isolated Sso1, in contrast to results obtained with the neuronal homologues syntaxin 1 and Munc18-1.

    CAS  PubMed  PubMed Central  Google Scholar 

  16. Yamaguchi, T. et al. Sly1 binds to Golgi and ER syntaxins via a conserved N-terminal peptide motif. Dev. Cell 2, 295–305 (2002).

    CAS  PubMed  Google Scholar 

  17. Dulubova, I. et al. How Tlg2p/Syntaxin 16 'Snares' Vps45. EMBO J. 21, 3620–3631 (2002).References 16 and 17 reveal a novel, evolutionarily conserved mode of coupling between syntaxins and SM proteins that acts in several cellular compartments and is markedly different from the interaction between the neuronal syntaxin 1 and Munc18-1, indicating that the latter interaction constitutes a specialization rather than a paradigm.

    CAS  PubMed  PubMed Central  Google Scholar 

  18. Lin, R. C. & Scheller, R. H. Mechanisms of synaptic vesicle exocytosis. Annu. Rev. Cell Dev. Biol. 16, 19–49 (2000).

    CAS  PubMed  Google Scholar 

  19. Fasshauer, D., Sutton, R. B., Brunger, A. T. & Jahn, R. Conserved structural features of the synaptic fusion complex: SNARE proteins reclassified as Q- and R-SNAREs. Proc. Natl Acad. Sci. USA 95, 15781–15786 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  20. Pelham, H. R. SNAREs and the secretory pathway — lessons from yeast. Exp. Cell Res. 247, 1–8 (1999).

    CAS  PubMed  Google Scholar 

  21. Schiavo, G. et al. Tetanus and botulinum-B neurotoxins block neurotransmitter release by proteolytic cleavage of synaptobrevin. Nature 359, 832–835 (1992).

    CAS  PubMed  Google Scholar 

  22. Link, E. et al. Tetanus toxin action: inhibition of neurotransmitter release linked to synaptobrevin proteolysis. Biochem. Biophys. Res. Commun. 189, 1017–1023 (1992).References 21 and 22 show that synaptobrevin is the target of clostridial neurotoxins, demonstrating for the first time the functional importance of a SNARE protein for neurotransmitter release.

    CAS  PubMed  Google Scholar 

  23. Blasi, J. et al. Botulinum neurotoxin A selectively cleaves the synaptic protein SNAP-25. Nature 365, 160–163 (1993).

    CAS  PubMed  Google Scholar 

  24. Blasi, J. et al. Botulinum neurotoxin C1 blocks neurotransmitter release by means of cleaving HPC-1/syntaxin. EMBO J. 12, 4821–4828 (1993).

    CAS  PubMed  PubMed Central  Google Scholar 

  25. Schulze, K. L., Broadie, K., Perin, M. S. & Bellen, H. J. Genetic and electrophysiological studies of Drosophila syntaxin-1A demonstrate its role in nonneuronal secretion and neurotransmission. Cell 80, 311–320 (1995).

    CAS  PubMed  Google Scholar 

  26. Broadie, K. et al. Syntaxin and synaptobrevin function downstream of vesicle docking in Drosophila Neuron 15, 663–673 (1995).

    CAS  PubMed  Google Scholar 

  27. Sollner, T. et al. SNAP receptors implicated in vesicle targeting and fusion. Nature 362, 318–324 (1993).Elegant biochemical experiments showed that synaptobrevin, syntaxin and SNAP25 form a complex with NSF and SNAPs, providing a connection between proteins that function in membrane traffic at the Golgi and components of the neurotransmitter release machinery.

    CAS  PubMed  Google Scholar 

  28. Rothman, J. E. Mechanisms of intracellular protein transport. Nature 372, 55–63 (1994).

    CAS  PubMed  Google Scholar 

  29. Sollner, T., Bennett, M. K., Whiteheart, S. W., Scheller, R. H. & Rothman, J. E. A protein assembly–disassembly pathway in vitro that may correspond to sequential steps of synaptic vesicle docking, activation, and fusion. Cell 75, 409–418 (1993).This paper showed for the first time that synaptobrevin, syntaxin and SNAP25 form a complex (the core complex) that is disassembled by NSF/SNAPs.

    CAS  PubMed  Google Scholar 

  30. McMahon, H. T. & Sudhof, T. C. Synaptic core complex of synaptobrevin, syntaxin, and SNAP25 forms high affinity α-SNAP binding site. J. Biol. Chem. 270, 2213–2217 (1995).Biochemical experiments showed that the core complex, rather than the individual SNAREs, provides a high-affinity binding site for SNAPs and NSF.

    CAS  PubMed  Google Scholar 

  31. Hayashi, T. et al. Synaptic vesicle membrane fusion complex: action of clostridial neurotoxins on assembly. EMBO J. 13, 5051–5061 (1994).

    CAS  PubMed  PubMed Central  Google Scholar 

  32. Calakos, N., Bennett, M. K., Peterson, K. E. & Scheller, R. H. Protein–protein interactions contributing to the specificity of intracellular vesicular trafficking. Science 263, 1146–1149 (1994).

    CAS  PubMed  Google Scholar 

  33. Nichols, B. J., Ungermann, C., Pelham, H. R., Wickner, W. T. & Haas, A. Homotypic vacuolar fusion mediated by t- and v-SNAREs. Nature 387, 199–202 (1997).In vitro studies of vacuolar fusion showed that SNAREs are required on opposing membranes for biological fusion.

    CAS  PubMed  Google Scholar 

  34. Sudhof, T. C., De Camilli, P., Niemann, H. & Jahn, R. Membrane fusion machinery: insights from synaptic proteins. Cell 75, 1–4 (1993).

    CAS  PubMed  Google Scholar 

  35. Banerjee, A., Barry, V. A., DasGupta, B. R. & Martin, T. F. N-Ethylmaleimide-sensitive factor acts at a prefusion ATP-dependent step in Ca2+-activated exocytosis. J. Biol. Chem. 271, 20223–20226 (1996).

    CAS  PubMed  Google Scholar 

  36. Mayer, A., Wickner, W. & Haas, A. Sec18p (NSF)-driven release of Sec17p (α-SNAP) can precede docking and fusion of yeast vacuoles. Cell 85, 83–94 (1996).Elegant studies of yeast vacuolar fusion showed that NSF functions at a step that is distinct from membrane fusion.

    CAS  PubMed  Google Scholar 

  37. Poirier, M. A. et al. Protease resistance of syntaxin. SNAP-25.VAMP complexes. Implications for assembly and structure. J. Biol. Chem. 273, 11370–11377 (1998).

    CAS  PubMed  Google Scholar 

  38. Fasshauer, D., Eliason, W. K., Brunger, A. T. & Jahn, R. Identification of a minimal core of the synaptic SNARE complex sufficient for reversible assembly and disassembly. Biochemistry 37, 10354–10362 (1998).

    CAS  PubMed  Google Scholar 

  39. Dulubova, I. et al. A conformational switch in syntaxin during exocytosis: role of Munc18. EMBO J. 18, 4372–4382 (1999).A combination of NMR, biochemical and functional experiments showed that the amino-terminal H abc domain of syntaxin 1 folds back onto the SNARE motif, forming a closed conformation that is crucial for binding to Munc18-1, but is incompatible with the core complex.

    CAS  PubMed  PubMed Central  Google Scholar 

  40. Poirier, M. A. et al. The synaptic SNARE complex is a parallel four-stranded helical bundle. Nature Struct. Biol. 5, 765–769 (1998).

    CAS  PubMed  Google Scholar 

  41. Sutton, R. B., Fasshauer, D., Jahn, R. & Brunger, A. T. Crystal structure of a SNARE complex involved in synaptic exocytosis at 2.4 Å resolution. Nature 395, 347–353 (1998).X-ray crystallography revealed the three-dimensional structure of the core complex at atomic resolution, providing a structural basis to understand SNARE function.

    CAS  PubMed  Google Scholar 

  42. Nicholson, K. L. et al. Regulation of SNARE complex assembly by an N-terminal domain of the t-SNARE Sso1p. Nature Struct. Biol. 5, 793–802 (1998).

    CAS  PubMed  Google Scholar 

  43. Fiebig, K. M., Rice, L. M., Pollock, E. & Brunger, A. T. Folding intermediates of SNARE complex assembly. Nature Struct. Biol. 6, 117–123 (1999).

    CAS  PubMed  Google Scholar 

  44. Paumet, F. et al. A t-SNARE of the endocytic pathway must be activated for fusion. J. Cell Biol. 155, 961–968 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  45. Parlati, F. et al. Distinct SNARE complexes mediating membrane fusion in Golgi transport based on combinatorial specificity. Proc. Natl Acad. Sci. USA 99, 5424–5429 (2002).

    CAS  PubMed  PubMed Central  Google Scholar 

  46. Antonin, W., Fasshauer, D., Becker, S., Jahn, R. & Schneider, T. R. Crystal structure of the endosomal SNARE complex reveals common structural principles of all SNAREs. Nature Struct. Biol. 9, 107–111 (2002).

    CAS  PubMed  Google Scholar 

  47. Weber, T. et al. SNAREpins are functionally resistant to disruption by NSF and αSNAP. J. Cell Biol. 149, 1063–1072 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  48. Misura, K. M., Gonzalez, L. C. Jr, May, A. P., Scheller, R. H. & Weis, W. I. Crystal structure and biophysical properties of a complex between the N-terminal SNARE region of SNAP25 and syntaxin 1a. J. Biol. Chem. 276, 41301–41309 (2001).

    CAS  PubMed  Google Scholar 

  49. Nagiec, E. E., Bernstein, A. & Whiteheart, S. W. Each domain of the N-ethylmaleimide-sensitive fusion protein contributes to its transport activity. J. Biol. Chem. 270, 29182–29188 (1995).

    CAS  PubMed  Google Scholar 

  50. Whiteheart, S. W. et al. N-Ethylmaleimide-sensitive fusion protein: a trimeric ATPase whose hydrolysis of ATP is required for membrane fusion. J. Cell Biol. 126, 945–954 (1994).

    CAS  PubMed  Google Scholar 

  51. Lenzen, C. U., Steinmann, D., Whiteheart, S. W. & Weis, W. I. Crystal structure of the hexamerization domain of N-ethylmaleimide-sensitive fusion protein. Cell 94, 525–536 (1998).

    CAS  PubMed  Google Scholar 

  52. Yu, R. C., Hanson, P. I., Jahn, R. & Brunger, A. T. Structure of the ATP-dependent oligomerization domain of N-ethylmaleimide sensitive factor complexed with ATP. Nature Struct. Biol. 5, 803–811 (1998).

    CAS  PubMed  Google Scholar 

  53. May, A. P., Misura, K. M., Whiteheart, S. W. & Weis, W. I. Crystal structure of the amino-terminal domain of N-ethylmaleimide-sensitive fusion protein. Nature Cell Biol. 1, 175–182 (1999).

    CAS  PubMed  Google Scholar 

  54. Yu, R. C., Jahn, R. & Brunger, A. T. NSF N-terminal domain crystal structure: models of NSF function. Mol. Cell 4, 97–107 (1999).

    CAS  PubMed  Google Scholar 

  55. Babor, S. M. & Fass, D. Crystal structure of the Sec18p N-terminal domain. Proc. Natl Acad. Sci. USA 96, 14759–14764 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  56. Rice, L. M. & Brunger, A. T. Crystal structure of the vesicular transport protein Sec17: implications for SNAP function in SNARE complex disassembly. Mol. Cell 4, 85–95 (1999).

    CAS  PubMed  Google Scholar 

  57. Hohl, T. M. et al. Arrangement of subunits in 20 S particles consisting of NSF, SNAPs, and SNARE complexes. Mol. Cell 2, 539–548 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  58. Schweizer, F. E. et al. Regulation of neurotransmitter release kinetics by NSF. Science 279, 1203–1206 (1998).

    CAS  PubMed  Google Scholar 

  59. Littleton, J. T. et al. Temperature-sensitive paralytic mutations demonstrate that synaptic exocytosis requires SNARE complex assembly and disassembly. Neuron 21, 401–413 (1998).

    CAS  PubMed  Google Scholar 

  60. Kawasaki, F., Mattiuz, A. M. & Ordway, R. W. Synaptic physiology and ultrastructure in comatose mutants define an in vivo role for NSF in neurotransmitter release. J. Neurosci. 18, 10241–10249 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  61. Tolar, L. A. & Pallanck, L. NSF function in neurotransmitter release involves rearrangement of the SNARE complex downstream of synaptic vesicle docking. J. Neurosci. 18, 10250–10256 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  62. Littleton, J. T. et al. SNARE-complex disassembly by NSF follows synaptic-vesicle fusion. Proc. Natl Acad. Sci. USA 98, 12233–12238 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  63. Muller, J. M. et al. An NSF function distinct from ATPase-dependent SNARE disassembly is essential for Golgi membrane fusion. Nature Cell Biol. 1, 335–340 (1999).

    CAS  PubMed  Google Scholar 

  64. Skehel, J. J. & Wiley, D. C. Coiled coils in both intracellular vesicle and viral membrane fusion. Cell 95, 871–874 (1998).

    CAS  PubMed  Google Scholar 

  65. Fasshauer, D., Antonin, W., Subramaniam, V. & Jahn, R. SNARE assembly and disassembly exhibit a pronounced hysteresis. Nature Struct. Biol. 9, 144–151 (2002).

    CAS  PubMed  Google Scholar 

  66. Zimmerberg, J. & Chernomordik, L. V. Membrane fusion. Adv. Drug Deliv. Rev. 38, 197–205 (1999).

    CAS  PubMed  Google Scholar 

  67. Nickel, W. et al. Content mixing and membrane integrity during membrane fusion driven by pairing of isolated v-SNAREs and t-SNAREs. Proc. Natl Acad. Sci. USA 96, 12571–12576 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  68. Otter-Nilsson, M., Hendriks, R., Pecheur-Huet, E. I., Hoekstra, D. & Nilsson, T. Cytosolic ATPases, p97 and NSF, are sufficient to mediate rapid membrane fusion. EMBO J. 18, 2074–2083 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  69. Brugger, B. et al. Putative fusogenic activity of NSF is restricted to a lipid mixture whose coalescence is also triggered by other factors. EMBO J. 19, 1272–1278 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  70. Langosch, D. et al. Peptide mimics of SNARE transmembrane segments drive membrane fusion depending on their conformational plasticity. J. Mol. Biol. 311, 709–721 (2001).

    CAS  PubMed  Google Scholar 

  71. Hu, K. et al. Vesicular restriction of synaptobrevin suggests a role for calcium in membrane fusion. Nature 415, 646–650 (2002).

    CAS  PubMed  Google Scholar 

  72. Chen, Y. A., Scales, S. J., Patel, S. M., Doung, Y. C. & Scheller, R. H. SNARE complex formation is triggered by Ca2+ and drives membrane fusion. Cell 97, 165–174 (1999).

    CAS  PubMed  Google Scholar 

  73. Chen, Y. A. et al. Calcium regulation of exocytosis in PC12 cells. J. Biol. Chem. 276, 26680–26687 (2001).

    CAS  PubMed  Google Scholar 

  74. Xia, Z., Zhou, Q., Lin, J. & Liu, Y. Stable SNARE complex prior to evoked synaptic vesicle fusion revealed by fluorescence resonance energy transfer. J. Biol. Chem. 276, 1766–1771 (2001).

    CAS  PubMed  Google Scholar 

  75. Peters, C. & Mayer, A. Ca2+/calmodulin signals the completion of docking and triggers a late step of vacuole fusion. Nature 396, 575–580 (1998).

    CAS  PubMed  Google Scholar 

  76. Peters, C. et al. Control of the terminal step of intracellular membrane fusion by protein phosphatase 1. Science 285, 1084–1087 (1999).

    CAS  PubMed  Google Scholar 

  77. Wang, L., Seeley, E. S., Wickner, W. & Merz, A. J. Vacuole fusion at a ring of vertex docking sites leaves membrane fragments within the organelle. Cell 108, 357–369 (2002).

    CAS  PubMed  Google Scholar 

  78. David, D., Sundarababu, S. & Gerst, J. E. Involvement of long chain fatty acid elongation in the trafficking of secretory vesicles in yeast. J. Cell Biol. 143, 1167–1182 (1998).The observation that genes involved in controlling lipid metabolism can rescue the lethal phenotype caused by mutations in Snc1 and Snc2 indicates that SNAREs might not be essential for membrane fusion.

    CAS  PubMed  PubMed Central  Google Scholar 

  79. Sweeney, S. T., Broadie, K., Keane, J., Niemann, H. & O'Kane, C. J. Targeted expression of tetanus toxin light chain in Drosophila specifically eliminates synaptic transmission and causes behavioral defects. Neuron 14, 341–351 (1995).

    CAS  PubMed  Google Scholar 

  80. Deitcher, D. L. et al. Distinct requirements for evoked and spontaneous release of neurotransmitter are revealed by mutations in the Drosophila gene neuronal-synaptobrevin. J. Neurosci. 18, 2028–2039 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  81. Saifee, O., Wei, L. & Nonet, M. L. The Caenorhabditis elegans unc-64 locus encodes a syntaxin that interacts genetically with synaptobrevin. Mol. Biol. Cell 9, 1235–1252 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  82. Nonet, M. L., Saifee, O., Zhao, H., Rand, J. B. & Wei, L. Synaptic transmission deficits in Caenorhabditis elegans synaptobrevin mutants. J. Neurosci. 18, 70–80 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  83. Washbourne, P. et al. Genetic ablation of the t-SNARE SNAP-25 distinguishes mechanisms of neuroexocytosis. Nature Neurosci. 5, 19–26 (2002).

    CAS  PubMed  Google Scholar 

  84. Sorensen, J. B. et al. The SNARE protein SNAP-25 is linked to fast calcium triggering of exocytosis. Proc. Natl Acad. Sci. USA 99, 1627–1632 (2002).

    CAS  PubMed  PubMed Central  Google Scholar 

  85. Garcia, E. P., McPherson, P. S., Chilcote, T. J., Takei, K. & De Camilli, P. rbSec1A and B colocalize with syntaxin 1 and SNAP-25 throughout the axon, but are not in a stable complex with syntaxin. J. Cell Biol. 129, 105–120 (1995).

    CAS  PubMed  Google Scholar 

  86. Waters, M. G. & Hughson, F. M. Membrane tethering and fusion in the secretory and endocytic pathways. Traffic 1, 588–597 (2000).

    CAS  PubMed  Google Scholar 

  87. Pfeffer, S. R. Rab GTPases: specifying and deciphering organelle identity and function. Trends Cell Biol. 11, 487–491 (2001).

    CAS  PubMed  Google Scholar 

  88. Misura, K. M., Scheller, R. H. & Weis, W. I. Self-association of the H3 region of syntaxin 1A. Implications for intermediates in SNARE complex assembly. J. Biol. Chem. 276, 13273–13282 (2001).

    CAS  PubMed  Google Scholar 

  89. Xiao, W., Poirier, M. A., Bennett, M. K. & Shin, Y. K. The neuronal t-SNARE complex is a parallel four-helix bundle. Nature Struct. Biol. 8, 308–311 (2001).

    CAS  PubMed  Google Scholar 

  90. Yang, B. et al. SNARE interactions are not selective. Implications for membrane fusion specificity. J. Biol. Chem. 274, 5649–5653 (1999).

    CAS  PubMed  Google Scholar 

  91. Fasshauer, D., Antonin, W., Margittai, M., Pabst, S. & Jahn, R. Mixed and non-cognate SNARE complexes. Characterization of assembly and biophysical properties. J. Biol. Chem. 274, 15440–15446 (1999).References 90 and 91 show that non-cognate combinations of SNAREs can form highly stable complexes, indicating that SNAREs are more promiscuous than was previously thought.

    CAS  PubMed  Google Scholar 

  92. Scales, S. J. et al. SNAREs contribute to the specificity of membrane fusion. Neuron 26, 457–464 (2000).

    CAS  PubMed  Google Scholar 

  93. Wang, Y., Dulubova, I., Rizo, J. & Sudhof, T. C. Functional analysis of conserved structural elements in yeast syntaxin Vam3p. J. Biol. Chem. 276, 28598–28605 (2001).

    CAS  PubMed  Google Scholar 

  94. Von Mollard, G. F., Nothwehr, S. F. & Stevens, T. H. The yeast v-SNARE Vti1p mediates two vesicle transport pathways through interactions with the t-SNAREs Sed5p and Pep12p. J. Cell Biol. 137, 1511–1524 (1997).This paper provides some of the most convincing evidence that a SNARE can function in more than one membrane-traffic pathway.

    CAS  PubMed  PubMed Central  Google Scholar 

  95. Lupashin, V. V., Pokrovskaya, I. D., McNew, J. A. & Waters, M. G. Characterization of a novel yeast SNARE protein implicated in Golgi retrograde traffic. Mol. Biol. Cell 8, 2659–2676 (1997).

    CAS  PubMed  PubMed Central  Google Scholar 

  96. Lian, J. P. & Ferro-Novick, S. Bos1p, an integral membrane protein of the endoplasmic reticulum to Golgi transport vesicles, is required for their fusion competence. Cell 73, 735–745 (1993).

    CAS  PubMed  Google Scholar 

  97. Katz, L. & Brennwald, P. Testing the 3Q:1R 'rule': mutational analysis of the ionic 'zero' layer in the yeast exocytic SNARE complex reveals no requirement for arginine. Mol. Biol. Cell 11, 3849–3858 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  98. Ossig, R. et al. Exocytosis requires asymmetry in the central layer of the SNARE complex. EMBO J. 19, 6000–6010 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  99. Scales, S. J., Yoo, B. Y. & Scheller, R. H. The ionic layer is required for efficient dissociation of the SNARE complex by α-SNAP and NSF. Proc. Natl Acad. Sci. USA 98, 14262–14267 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  100. Hata, Y., Slaughter, C. A. & Sudhof, T. C. Synaptic vesicle fusion complex contains unc-18 homologue bound to syntaxin. Nature 366, 347–351 (1993).The paper describes the isolation of a syntaxin-binding protein that was found to be homologous to C. elegans UNC-18 and yeast Sec1.

    CAS  PubMed  Google Scholar 

  101. Fernandez, I. et al. Three-dimensional structure of an evolutionarily conserved N-terminal domain of syntaxin 1A. Cell 94, 841–849 (1998).The NMR structure of the H abc domain of syntaxin 1 is described, providing the first structural information at atomic resolution for a SNARE protein.

    CAS  PubMed  Google Scholar 

  102. Misura, K. M., Scheller, R. H. & Weis, W. I. Three-dimensional structure of the neuronal-Sec1–syntaxin 1a complex. Nature 404, 355–362 (2000).The X-ray structure of Munc18-1 bound to syntaxin 1 provided the first three-dimensional structure of an SM protein and, at the same time, revealed at atomic detail the closed conformation of syntaxin 1, as well as its interaction with Munc18-1.

    CAS  PubMed  Google Scholar 

  103. Munson, M., Chen, X., Cocina, A. E., Schultz, S. M. & Hughson, F. M. Interactions within the yeast t-SNARE Sso1p that control SNARE complex assembly. Nature Struct. Biol. 7, 894–902 (2000).

    CAS  PubMed  Google Scholar 

  104. Dulubova, I., Yamaguchi, T., Wang, Y., Sudhof, T. C. & Rizo, J. Vam3p structure reveals conserved and divergent properties of syntaxins. Nature Struct. Biol. 8, 258–264 (2001).

    CAS  PubMed  Google Scholar 

  105. Munson, M. & Hughson, F. M. Conformational regulation of SNARE assembly and disassembly in vivo. J. Biol. Chem. 277, 9375–9381 (2002).

    CAS  PubMed  Google Scholar 

  106. Tochio, H., Tsui, M. M., Banfield, D. K. & Zhang, M. An autoinhibitory mechanism for nonsyntaxin SNARE proteins revealed by the structure of Ykt6p. Science 293, 698–702 (2001).

    CAS  PubMed  Google Scholar 

  107. Cheever, M. L. et al. Phox domain interaction with PtdIns3P targets the Vam7 t-SNARE to vacuole membranes. Nature Cell Biol. 3, 613–618 (2001).

    CAS  PubMed  Google Scholar 

  108. Brenner, S. The genetics of Caenorhabditis elegans. Genetics 77, 71–94 (1974).

    CAS  PubMed  PubMed Central  Google Scholar 

  109. Novick, P., Field, C. & Schekman, R. Identification of 23 complementation groups required for post-translational events in the yeast secretory pathway. Cell 21, 205–215 (1980).References 108 and 109 describe seminal studies that illustrate the power of genetic screens, and identify unc-18 and Sec1 among other genes that are involved in neurotransmission in C. elegans (reference 108 ) and in secretion in yeast (reference 109).

    CAS  PubMed  Google Scholar 

  110. Hosono, R. et al. The unc-18 gene encodes a novel protein affecting the kinetics of acetylcholine metabolism in the nematode Caenorhabditis elegans. J. Neurochem. 58, 1517–1525 (1992).

    CAS  PubMed  Google Scholar 

  111. Ossig, R., Dascher, C., Trepte, H. H., Schmitt, H. D. & Gallwitz, D. The yeast SLY gene products, suppressors of defects in the essential GTP-binding Ypt1 protein, may act in endoplasmic reticulum-to-Golgi transport. Mol. Cell. Biol. 11, 2980–2993 (1991).

    CAS  PubMed  PubMed Central  Google Scholar 

  112. Schekman, R. Genetic and biochemical analysis of vesicular traffic in yeast. Curr. Opin. Cell Biol. 4, 587–592 (1992).

    CAS  PubMed  Google Scholar 

  113. Harrison, S. D., Broadie, K., van de Goor, J. & Rubin, G. M. Mutations in the Drosophila Rop gene suggest a function in general secretion and synaptic transmission. Neuron 13, 555–566 (1994).

    CAS  PubMed  Google Scholar 

  114. Verhage, M. et al. Synaptic assembly of the brain in the absence of neurotransmitter secretion. Science 287, 864–869 (2000).Deletion of Munc18-1 in mice resulted in a phenotype in which neurotransmitter release was completely abolished, but normal brain assembly was observed.

    CAS  PubMed  Google Scholar 

  115. Voets, T. et al. Munc18-1 promotes large dense-core vesicle docking. Neuron 31, 581–591 (2001).

    CAS  PubMed  Google Scholar 

  116. Grote, E., Carr, C. M. & Novick, P. J. Ordering the final events in yeast exocytosis. J. Cell Biol. 151, 439–452 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  117. Pevsner, J., Hsu, S. C. & Scheller, R. H. n-Sec1: a neural-specific syntaxin-binding protein. Proc. Natl Acad. Sci. USA 91, 1445–1449 (1994).

    CAS  PubMed  PubMed Central  Google Scholar 

  118. Garcia, E. P., Gatti, E., Butler, M., Burton, J. & De Camilli, P. A rat brain Sec1 homologue related to Rop and UNC18 interacts with syntaxin. Proc. Natl Acad. Sci. USA 91, 2003–2007 (1994).

    CAS  PubMed  PubMed Central  Google Scholar 

  119. Sogaard, M. et al. A rab protein is required for the assembly of SNARE complexes in the docking of transport vesicles. Cell 78, 937–948 (1994).

    CAS  PubMed  Google Scholar 

  120. Grabowski, R. & Gallwitz, D. High-affinity binding of the yeast cis-Golgi t-SNARE, Sed5p, to wild-type and mutant Sly1p, a modulator of transport vesicle docking. FEBS Lett. 411, 169–172 (1997).

    CAS  PubMed  Google Scholar 

  121. Nichols, B. J., Holthuis, J. C. & Pelham, H. R. The Sec1p homologue Vps45p binds to the syntaxin Tlg2p. Eur. J. Cell Biol. 77, 263–268 (1998).

    CAS  PubMed  Google Scholar 

  122. Abeliovich, H., Darsow, T. & Emr, S. D. Cytoplasm to vacuole trafficking of aminopeptidase I requires a t-SNARE–Sec1p complex composed of Tlg2p and Vps45p. EMBO J. 18, 6005–6016 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  123. Yang, B., Steegmaier, M., Gonzalez, L. C. Jr & Scheller, R. H. nSec1 binds a closed conformation of syntaxin1A. J. Cell Biol. 148, 247–252 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  124. Wu, M. N. et al. Syntaxin 1A interacts with multiple exocytic proteins to regulate neurotransmitter release in vivo. Neuron 23, 593–605 (1999).

    CAS  PubMed  Google Scholar 

  125. Wu, M. N., Littleton, J. T., Bhat, M. A., Prokop, A. & Bellen, H. J. ROP, the Drosophila Sec1 homolog, interacts with syntaxin and regulates neurotransmitter release in a dosage-dependent manner. EMBO J. 17, 127–139 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  126. Bracher, A., Perrakis, A., Dresbach, T., Betz, H. & Weissenhorn, W. The X-ray crystal structure of neuronal Sec1 from squid sheds new light on the role of this protein in exocytosis. Structure Fold. Des. 8, 685–694 (2000).

    CAS  PubMed  Google Scholar 

  127. Maruyama, I. N. & Brenner, S. A phorbol ester/diacylglycerol-binding protein encoded by the unc-13 gene of Caenorhabditis elegans. Proc. Natl Acad. Sci. USA 88, 5729–5733 (1991).

    CAS  PubMed  PubMed Central  Google Scholar 

  128. Brose, N., Hofmann, K., Hata, Y. & Sudhof, T. C. Mammalian homologues of Caenorhabditis elegans unc-13 gene define novel family of C2-domain proteins. J. Biol. Chem. 270, 25273–25280 (1995).

    CAS  PubMed  Google Scholar 

  129. Augustin, I., Rosenmund, C., Sudhof, T. C. & Brose, N. Munc13-1 is essential for fusion competence of glutamatergic synaptic vesicles. Nature 400, 457–461 (1999).

    CAS  PubMed  Google Scholar 

  130. Richmond, J. E., Davis, W. S. & Jorgensen, E. M. UNC-13 is required for synaptic vesicle fusion in C. elegans. Nature Neurosci. 2, 959–964 (1999).

    CAS  PubMed  Google Scholar 

  131. Aravamudan, B., Fergestad, T., Davis, W. S., Rodesch, C. K. & Broadie, K. Drosophila UNC-13 is essential for synaptic transmission. Nature Neurosci. 2, 965–971 (1999).

    CAS  PubMed  Google Scholar 

  132. Rosenmund, C. et al. Differential control of vesicle priming and short-term plasticity by Munc13 isoforms. Neuron 33, 411–424 (2002).

    CAS  PubMed  Google Scholar 

  133. Wang, Y., Okamoto, M., Schmitz, F., Hofmann, K. & Sudhof, T. C. Rim is a putative Rab3 effector in regulating synaptic-vesicle fusion. Nature 388, 593–598 (1997).

    CAS  PubMed  Google Scholar 

  134. Koushika, S. P. et al. A post-docking role for active zone protein Rim. Nature Neurosci. 4, 997–1005 (2001).

    CAS  PubMed  Google Scholar 

  135. Schoch, S. et al. RIM1 α forms a protein scaffold for regulating neurotransmitter release at the active zone. Nature 415, 321–326 (2002).

    CAS  PubMed  Google Scholar 

  136. Betz, A., Okamoto, M., Benseler, F. & Brose, N. Direct interaction of the rat unc-13 homologue Munc13-1 with the N terminus of syntaxin. J. Biol. Chem. 272, 2520–2526 (1997).

    CAS  PubMed  Google Scholar 

  137. Sassa, T. et al. Regulation of the UNC-18–Caenorhabditis elegans syntaxin complex by UNC-13. J. Neurosci. 19, 4772–4777 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  138. Betz, A. et al. Functional interaction of the active zone proteins Munc13-1 and RIM1 in synaptic vesicle priming. Neuron 30, 183–196 (2001).

    CAS  PubMed  Google Scholar 

  139. Richmond, J. E., Weimer, R. M. & Jorgensen, E. M. An open form of syntaxin bypasses the requirement for UNC-13 in vesicle priming. Nature 412, 338–341 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  140. Fujita, Y. et al. Tomosyn: a syntaxin-1-binding protein that forms a novel complex in the neurotransmitter release process. Neuron 20, 905–915 (1998).

    CAS  PubMed  Google Scholar 

  141. Fujita, Y. et al. Phosphorylation of Munc-18/n-Sec1/rbSec1 by protein kinase C: its implication in regulating the interaction of Munc-18/n-Sec1/rbSec1 with syntaxin. J. Biol. Chem. 271, 7265–7268 (1996).

    CAS  PubMed  Google Scholar 

  142. Shuang, R. et al. Regulation of Munc-18/syntaxin 1A interaction by cyclin-dependent kinase 5 in nerve endings. J. Biol. Chem. 273, 4957–4966 (1998).

    CAS  PubMed  Google Scholar 

  143. Okamoto, M. & Sudhof, T. C. Mints, Munc18-interacting proteins in synaptic vesicle exocytosis. J. Biol. Chem. 272, 31459–31464 (1997).

    CAS  PubMed  Google Scholar 

  144. Verhage, M. et al. DOC2 proteins in rat brain: complementary distribution and proposed function as vesicular adapter proteins in early stages of secretion. Neuron 18, 453–461 (1997).

    CAS  PubMed  Google Scholar 

  145. Bryant, N. J. & James, D. E. Vps45p stabilizes the syntaxin homologue Tlg2p and positively regulates SNARE complex formation. EMBO J. 20, 3380–3388 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  146. Peng, R. & Gallwitz, D. Sly1 protein bound to Golgi syntaxin Sed5p allows assembly and contributes to specificity of SNARE fusion complexes. J. Cell Biol. 157, 645–655 (2002).

    CAS  PubMed  PubMed Central  Google Scholar 

  147. Fernandez-Chacon, R. et al. Synaptotagmin I functions as a calcium regulator of release probability. Nature 410, 41–49 (2001).Correlation of biochemical experiments with electrophysiological analyses of knock-in mice that have mutations in synaptotagmin 1 established the role of this protein as a Ca2+ sensor in neurotransmitter release.

    CAS  PubMed  Google Scholar 

  148. Sudhof, T. C. Synaptotagmins: why so many? J. Biol. Chem. 277, 7629–7632 (2002).

    CAS  PubMed  Google Scholar 

  149. McMahon, H. T., Missler, M., Li, C. & Sudhof, T. C. Complexins: cytosolic proteins that regulate SNAP receptor function. Cell 83, 111–119 (1995).In this study, complexins were identified as proteins that bind specifically to the neuronal core complex.

    CAS  PubMed  Google Scholar 

  150. Takahashi, S. et al. Identification of two highly homologous presynaptic proteins distinctly localized at the dendritic and somatic synapses. FEBS Lett. 368, 455–460 (1995).

    CAS  PubMed  Google Scholar 

  151. Ishizuka, T., Saisu, H., Odani, S. & Abe, T. Synaphin: a protein associated with the docking/fusion complex in presynaptic terminals. Biochem. Biophys. Res. Commun. 213, 1107–1114 (1995).

    CAS  PubMed  Google Scholar 

  152. Reim, K. et al. Complexins regulate a late step in Ca2+-dependent neurotransmitter release. Cell 104, 71–81 (2001).

    CAS  PubMed  Google Scholar 

  153. Tokumaru, H. et al. SNARE complex oligomerization by synaphin/complexin is essential for synaptic vesicle exocytosis. Cell 104, 421–432 (2001).

    CAS  PubMed  Google Scholar 

  154. Pabst, S. et al. Rapid and selective binding to the synaptic SNARE complex suggests a modulatory role of complexins in neuroexocytosis. J. Biol. Chem. 277, 7838–7848 (2002).

    CAS  PubMed  Google Scholar 

  155. Pabst, S. et al. Selective interaction of complexin with the neuronal SNARE complex. Determination of the binding regions. J. Biol. Chem. 275, 19808–19818 (2000).

    CAS  PubMed  Google Scholar 

  156. Chen, X. et al. Three-dimensional structure of the complexin/SNARE complex. Neuron 33, 397–409 (2002).A combination of NMR spectroscopy and X-ray crystallography yielded the first three-dimensional structure of the core complex bound to another protein, complexin, and provided insight into the function of complexin in neurotransmitter release.

    CAS  PubMed  Google Scholar 

  157. Koradi, R., Billeter, M. & Wuthrich, K. MOLMOL: a program for display and analysis of macromolecular structures. J. Mol. Graph. 14, 51–32 (1996).

    CAS  PubMed  Google Scholar 

Download references

Author information

Authors and Affiliations

Authors

Related links

Related links

DATABASES

FlyBase

comatose

Rop

LocusLink

bassoon

complexin 1

complexin 2

Munc13-1

Munc18-1

NSF

piccolo

Rab3

RIM

SNAP25

SNAPs

synaptobrevin

synaptotagmin 1

syntaxin 1

syntaxin 16

syntaxin 18

syntaxin 5

<i>Saccharomyces</i> Genome Database

Bos1

Pep12

Sec1

Sec9

Sec17

Sec18

Sed5

Sly1

Snc1

Snc2

Sso1

Tlg2

Ufe1

Vam3

Vps33

Vps45

Vti1

WormBase

UNC-13

UNC-18

FURTHER INFORMATION

Encyclopedia of Life Sciences

calcium and neurotransmitter release

chemical synapses

synaptic vesicle traffic

Glossary

ELECTRON PARAMAGNETIC RESONANCE

(EPR). A spectroscopic technique that detects chemical species that have unpaired electrons. EPR spectroscopy can provide molecular structural details that are inaccessible by any other analytical tool.

COILED COIL

A polypeptide structural motif that is formed by two or more intertwined α-helices. Coiled-coil domains often participate in protein–protein interactions, but can also be involved in intramolecular interactions that stabilize protein structures.

FLUORESCENCE RESONANCE ENERGY TRANSFER

(FRET). A spectroscopic technique that is based on the transfer of energy from the excited state of a donor moiety to an acceptor. The transfer efficiency depends on the distance between the donor and the acceptor. FRET is often used to estimate distances between macromolecular sites in the 20–100-Å range, or to study interactions between macromolecules in vivo.

KINETIC TRAP

A metastable state that cannot evolve or evolves slowly to a thermodynamically more stable state owing to a high energy barrier.

AAA SUPERFAMILY

A family of proteins that share a homologous ATPase module. Proteins from this family participate in diverse cellular processes, including membrane traffic, proteolysis and DNA replication.

CHAOTROPIC AGENT

An agent that disorganizes the structure of water and can denature proteins by disrupting hydrophobic interactions.

FUSION PORE

A pore that is formed after the two leaflets of two lipid bilayers merge to form a single continuous bilayer and the 'bottle neck' at the site of fusion expands outwards radially. In synaptic vesicle exocytosis, opening of the fusion pore connects the luminal side of the vesicles with the extracellular space, allowing neurotransmitter release.

INVERTED CONE LIPIDS

Lipids that have large head groups relative to the diameter of the acyl chain.

STALKS

Metastable states that are widely believed to be intermediates in membrane fusion and involve merger of the proximal leaflets of the two bilayers at small contact sites.

AMPHIPATHIC POLYPEPTIDE

A polypeptide with both hydrophobic and hydrophilic surfaces.

PC12 CELLS

Neuron-like cells that are derived from a malignant neural crest tumour (a phaeochromocytoma).

BOTULINUM NEUROTOXIN E

A lethal neurotoxin that is produced by clostridium bacteria.

CHROMAFFIN CELLS

Cells of the adrenal gland that store and secrete catecholamines. They are termed 'chromaffin' because of the ability of chromium salts to stain them.

α-LATROTOXIN

An agent that normally causes massive neurotransmitter release.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Rizo, J., Südhof, T. Snares and munc18 in synaptic vesicle fusion. Nat Rev Neurosci 3, 641–653 (2002). https://doi.org/10.1038/nrn898

Download citation

  • Issue Date:

  • DOI: https://doi.org/10.1038/nrn898

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing