Regulation of the priming of exocytosis and the dissociation of SNAP-25 and VAMP-2 in adrenal chromaffin cells

Abstract

The MgATP-dependent priming step of exocytosis has been suggested to be regulated negatively by GTP-binding protein G o in permeabilized adrenal chromaffin cells. We have reported that synaptosomal-associated protein of 25 kDa (SNAP-25) and vesicle-associated membrane protein 2 (VAMP-2) form a complex in chromaffin cells, and the complex dissociates during MgATP-dependent priming. In this study, we examined whether G o controls such dissociation of the SNAP-25/VAMP-2 complex in the regulation of priming. In digitonin-permeabilized cells, MgATP- γ-S which can be a phosphate donor for protein phosphorylation failed to cause priming and dissociation of the SNAP-25/VAMP-2 complex. Mastoparan, which directly activates G o, selectively inhibited priming and blocked dissociation of the SNAP-25/VAMP-2 complex. These results suggest that ATP hydrolysis and dissociation of the SNAP-25/VAMP-2 complex are responsible for priming. These results also suggest that dissociation of the complex is one of the sequential steps for priming controlled by G o.