EVIDENCE FOR INTERACTION OF THE FUSION PROTEIN ALPHA-SNAP WITH MEMBRANE LIPID

alpha-SNAP [soluble N-ethylmaleimide-sensitive fusion protein (NSF)-at tachment protein] is required for fusion of transport vesicles with th eir target membrane. In this study, we have examined the membrane-bind ing properties of alpha-SNAP, We have found that in several tissues a much larger amount of alpha-SNAP per unit weight of protein is bound t o membranes than is free in the cytosol. Biochemical analysis shows th at a fraction of alpha-SNAP behaves in ways characteristic of hydropho bic, lipid-associated proteins. These findings suggest that membrane b inding may be accounted for, at least in part, by interaction with mem brane lipid. Consistent with this idea, binding of newly synthesized a lpha-SNAP to brain membranes was found to be independent of functional SNAP receptors and could be accounted for by direct binding of alpha- SNAP to membrane lipid. Furthermore, membrane lipid enhanced the abili ty of alpha-SNAP to stimulate NSF-dependent ATPase activity.