title: Reconstitution of the vital functions of Munc18 and Munc13 in neurotransmitter release.
abstract: Neurotransmitter release depends critically on Munc18-1, Munc13, the Ca(2+) sensor synaptotagmin-1, and the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) syntaxin-1, synaptobrevin, and SNAP-25. In vitro reconstitutions have shown that syntaxin-1-SNAP-25 liposomes fuse efficiently with synaptobrevin liposomes in the presence of synaptotagmin-1-Ca(2+), but neurotransmitter release also requires Munc18-1 and Munc13 in vivo. We found that Munc18-1 could displace SNAP-25 from syntaxin-1 and that fusion of syntaxin-1-Munc18-1 liposomes with synaptobrevin liposomes required Munc13, in addition to SNAP-25 and synaptotagmin-1-Ca(2+). Moreover, when starting with syntaxin-1-SNAP-25 liposomes, NSF-α-SNAP disassembled the syntaxin-1-SNAP-25 heterodimers and abrogated fusion, which then required Munc18-1 and Munc13. We propose that fusion does not proceed through syntaxin-1-SNAP-25 heterodimers but starts with the syntaxin-1-Munc18-1 complex; Munc18-1 and Munc13 then orchestrate membrane fusion together with the SNAREs and synaptotagmin-1-Ca(2+) in an NSF- and SNAP-resistant manner.
authors.affiliation: Key Laboratory of Molecular Biophysics, Ministry of Education, and Institute of Biophysics and Biochemistry, Huazhong University of Science and Technology, Wuhan 430074, China. cong.ma7@gmail.com
authors.forename: Cong
authors.initials: C
authors.lastname: Ma
authors.forename: Lijing
authors.initials: L
authors.lastname: Su
authors.forename: Alpay B
authors.initials: AB
authors.lastname: Seven
authors.forename: Yibin
authors.initials: Y
authors.lastname: Xu
authors.forename: Josep
authors.initials: J
authors.lastname: Rizo
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D006801:Humans; D008081:Liposomes; D008561:Membrane Fusion; D008954:Models, Biological; D051938:Munc18 Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D050683:R-SNARE Proteins / Q000378:metabolism; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism; D050863:Synaptotagmin I / Q000378:metabolism; D050827:Syntaxin 1 / Q000378:metabolism
chemical_list: D008081:Liposomes; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D050683:R-SNARE Proteins; C494208:SNAP25 protein, human; C494213:Stx1a protein, rat; C497939:Stxbp1 protein, rat; D050825:Synaptosomal-Associated Protein 25; D050863:Synaptotagmin I; D050827:Syntaxin 1; C103912:Unc13a protein, rat; D002118:Calcium