title: SNARE bundle and syntaxin N-peptide constitute a minimal complement for Munc18-1 activation of membrane fusion.
abstract: Sec1/Munc18 (SM) proteins activate intracellular membrane fusion through binding to cognate SNAP receptor (SNARE) complexes. The synaptic target membrane SNARE syntaxin 1 contains a highly conserved H(abc) domain, which connects an N-peptide motif to the SNARE core domain and is thought to participate in the binding of Munc18-1 (the neuronal SM protein) to the SNARE complex. Unexpectedly, we found that mutation or complete removal of the H(abc) domain had no effect on Munc18-1 stimulation of fusion. The central cavity region of Munc18-1 is required to stimulate fusion but not through its binding to the syntaxin H(abc) domain. SNAP-25, another synaptic SNARE subunit, contains a flexible linker and exhibits an atypical conjoined Q(bc) configuration. We found that neither the linker nor the Q(bc) configuration is necessary for Munc18-1 promotion of fusion. As a result, Munc18-1 activates a SNARE complex with the typical configuration, in which each of the SNARE core domains is individually rooted in the membrane bilayer. Thus, the SNARE four-helix bundle and syntaxin N-peptide constitute a minimal complement for Munc18-1 activation of fusion.
authors.affiliation: Department of Molecular, University of Colorado at Boulder, Boulder, CO 80309, USA. jingshi.shen@colorado.edu
authors.forename: Jingshi
authors.initials: J
authors.lastname: Shen
authors.forename: Shailendra S
authors.initials: SS
authors.lastname: Rathore
authors.forename: Lavan
authors.initials: L
authors.lastname: Khandan
authors.forename: James E
authors.initials: JE
authors.lastname: Rothman
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D008561:Membrane Fusion / Q000502:physiology*; D051379:Mice; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary; D050825:Synaptosomal-Associated Protein 25 / Q000235:genetics / Q000378:metabolism*; D050827:Syntaxin 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D051938:Munc18 Proteins; D010455:Peptides; C497938:Stxbp1 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1