Similar effects of α- and β-SNAP on Ca 2+-regulated exocytosis

Abstract

Soluble N-ethylmaleimide-sensitive fusion protein attachment proteins (SNAP) proteins function in Ca 2+-regulated exocytosis. Recent work (Schiavo et al. (1996) Nature 378, 733–736) based on in vitro protein interactions has raised the possibility that α- and β-SNAPs have distinct roles in exocytosis. We have examined this possibility by comparing the activities of recombinant α- and β-SNAPs. Both these proteins were able to similarly bind NSF and activate its ATPase activity but to a lesser extent than γ-SNAP. When introduced into digitoninpermeabilised chromaffin cells, both α- and β-SNAP stimulated Ca 2+-regulated exocytosis in a MgATP-dependent manner. The dose-response relationships for these proteins were essentially the same and addition of both proteins did not lead to any further increase in exocytosis above that due to each protein alone. We conclude that α- and β-SNAPs are interchangeable isoforms with similar functions in regulated exocytosis.