Whereas in a paradigmatic structure an SM protein chaperone clamps its client SNARE shut, a second structure demonstrates that an SM protein can also hold its SNARE open to promote assembly.
During neurotransmitter release, calcium-induced membrane insertion of the C2B domain of Synaptotagmin re-orients the bound SNARE complex which dilates the fusion pore in a mechanical lever action.
Sec1/Munc18 (SM) proteins shield SNARE complexes from NSF/Sec18-mediated disassembly through cooperative binding interactions with SNARE complexes and the universal co-chaperone α-SNAP/Sec17.
A novel microscopy-based assay shows that dendritic cells encountering pathogenic stimuli form increased complexes of specific SNARE proteins, driving release of large amounts of inflammatory cytokines.
A few SNARE complexes suffice to fuse membranes, but many more are needed to dilate the nascent fusion pore by molecular crowding for efficient neurotransmitter or hormone release during exocytosis.
Electron-cryomicroscopy structures of the supercomplex of NSF, αSNAP, and neuronal SNAREs in the presence of ATP under non-hydrolyzing conditions at 3.9 Å resolution reveal interactions between the N-terminal residues of SNAP-25 and NSF.
The Munc18-1 protein promotes formation of the t-SNARE complex and the half-zippered SNARE complex, two rate-limiting steps of SNARE assembly, to enhance membrane fusion.
