The ATPase activity of N-ethylmaleimide-sensitive fusion protein (NSF) is regulated by soluble NSF attachment proteins.

N-Ethylmaleimide-sensitive fusion protein (NSF) is an ATPase required in multiple stages of the secretory and endocytic pathways. NSF requires other proteins for its action in vesicular transport including the soluble NSF attachment proteins (SNAPs), which act to bind NSF to integral membrane proteins. We have investigated the ATPase activity of NSF and its modulation by alpha- and gamma-SNAPs using His6-tagged recombinant proteins. His6-NSF possessed ATPase activity, which was enhanced in a dose-dependent manner by immobilized (i.e. plastic-adsorbed) but not soluble His6-tagged SNAPs. NSF displayed complex enzyme kinetics consistent with the possession of two ATPase domains with different affinities for ATP. SNAPs apparently enhanced NSF ATPase activity primarily by decreasing the Km of its low affinity site 100-fold. In vivo this effect would be predicted to sensitize the low affinity site to physiological ATP concentrations. Thus SNAPs could act as a molecular switch by "turning on" the normally dormant low affinity ATPase site of NSF.