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Spring-loaded unraveling of a single SNARE complex by NSF in one round of ATP turnover

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Science  27 Mar 2015:
Vol. 347, Issue 6229, pp. 1485-1489
DOI: 10.1126/science.aaa5267

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An explosive way to fuse membranes

The molecular machine that promotes membrane fusion during intracellular transport involves a number of so-called SNARE proteins. Ryu et al. describe the molecular mechanism by which two proteins —NSF and α-SNAP—disassemble SNARE complexes. A combination of single-molecule techniques resolved intermediate steps of the reaction. Surprisingly, unlike previously assumed, NSF did not unwind SNARE complexes processively. Instead, built-up tension was released in a single burst to “tear” the SNARE complex apart in a one-step global unfolding reaction.

Science, this issue p. 1485

Abstract

During intracellular membrane trafficking, N-ethylmaleimide-sensitive factor (NSF) and alpha-soluble NSF attachment protein (α-SNAP) disassemble the soluble NSF attachment protein receptor (SNARE) complex for recycling of the SNARE proteins. The molecular mechanism by which NSF disassembles the SNARE complex is largely unknown. Using single-molecule fluorescence spectroscopy and magnetic tweezers, we found that NSF disassembled a single SNARE complex in only one round of adenosine triphosphate (ATP) turnover. Upon ATP cleavage, the NSF hexamer developed internal tension with dissociation of phosphate ions. After latent time measuring tens of seconds, NSF released the built-up tension in a burst within 20 milliseconds, resulting in disassembly followed by immediate release of the SNARE proteins. Thus, NSF appears to use a “spring-loaded” mechanism to couple ATP hydrolysis and unfolding of substrate proteins.

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