Practice question

Cis-SNARE complexes formed post-fusion are extremely stable four-helix bundles with melting temperature above 90 Celsius requiring energy for recycling. Disassembly machinery uses ATP. Hexameric AAA+ ATPase NSF N-ethylmaleimide sensitive factor assembles as ring with two stacked ATPase tiers D1 catalytic and D2 structural. Adaptor alpha-SNAP soluble attachment protein binds grooves along rod-like bundle via tetratricopeptide repeats and recruits NSF via N domains interaction with SNAP C-terminus. ATP hydrolysis in D1 causes power stroke threading SNARE polypeptide through central pore with tyrosine pore loops analogous to unfoldase ClpX effectively unwinding helices into separate monomers for reuse. Reaction occurs cytosolic side immediately after fusion producing free syntaxin and SNAP-25 staying in target and VAMP ready for retrograde recycling via vesicles. Sar1 GTP binding governs COPII coat nucleation, while phosphorylation or ubiquitination not physiological triggers for separation. Without NSF ATPase trafficking stalls within minutes as free SNARE pool depletes blocking secretion and neurotransmission.