Mechanistic insights into the recycling machine of the SNARE complex

Evolutionarily conserved SNARE (Soluble N-ethylmaleimide sensitive factor Attachment protein REceptors) proteins form a complex that drives fusion between membranes in eukaryotes. SNARE complexes are disassembled by the ATPase NSF (N-ethylmaleimide Sensitive Factor), together with SNAP (Soluble NSF Attachment Protein) proteins, making individual SNAREs available for a subsequent round of fusion. Here we report structures of ATP- and ADP-bound NSF, and the NSF/SNAP/SNARE (20S) supercomplex determined by single-particle electron cryomicroscopy at near-atomic to sub-nanometer resolution without imposing symmetry. Large, potentially force-generating, conformational differences exist between ATP- and ADP-bound NSF. The 20S supercomplex exhibits broken symmetry, transitioning from six-fold symmetry of the NSF ATPase domains, to pseudo four-fold symmetry of the SNARE complex. SNAPs are interacting with the SNARE complex with an opposite structural twist, suggesting an unwinding mechanism. The interfaces between NSF, SNAPs, and SNAREs exhibit characteristic electrostatic patterns, suggesting how one NSF/SNAP species can act on many different SNARE complexes.