Selective stimulation of the D1 ATPase domain of N-ethylmaleimide-sensitive fusion protein (NSF) by soluble NSF attachment proteins.

N-Ethylmaleimide-sensitive fusion protein (NSF) is required for most intracellular membrane fusion events. NSF is recruited to membranes by soluble NSF attachment proteins (SNAPs) and membrane-resident SNAP receptor (SNARE) proteins. The 20 S complex of NSF/SNAPs/SNAREs disassembles when NSF hydrolyses ATP, and this disassembly event is believed to be essential for membrane fusion. SNAPs stimulate NSF ATPase activity, but it is not known which of NSF's two ATPase domains (D1 or D2) is affected. Using recombinant mutant NSFs defective in ATP hydrolysis in one domain only, we found that SNAPs stimulate NSF ATPase activity by a selective action on the D1 domain, yet had no effect on the D2 domain. Since the D1 domain of NSF is implicated in 20 S complex disassembly, this supports the idea that SNAP stimulation of NSF ATPase activity is required for membrane fusion.