Three steps forward, two steps back: mechanistic insights into the assembly and disassembly of the SNARE complex

Membrane fusion is a tightly controlled process in all eukaryotic cell types. The SNARE family of proteins is required for fusion throughout the exocytic and endocytic trafficking pathways. SNAREs on a transport vesicle interact with the cognate SNAREs on the target membrane, forming an incredibly stable SNARE complex that provides energy for the membranes to fuse, although many aspects of the mechanism remain elusive. Recent advances in single-molecule and high-resolution structural methods provide exciting new insights into how SNARE complexes assemble, including measurements of assembly energetics and identification of intermediates in the assembly pathway. These techniques were also key in elucidating mechanistic details into how the SNARE complex is disassembled, including details of the energetics required for ATP-dependent α-SNAP/NSF-mediated SNARE complex disassembly, and the structural changes that accompany ATP hydrolysis by the disassembly machinery. Additionally, SNARE complex formation and disassembly are tightly regulated processes; innovative biochemical and biophysical characterization has deepened our understanding of how these regulators work to control membrane fusion and exocytosis.