SIMILAR EFFECTS OF ALPHA-SNAP AND BETA-SNAP ON CA2-REGULATED EXOCYTOSIS()

Soluble N-ethylmaleimide-sensitive fusion protein attachment proteins (SNAP) proteins function in Ca2+-regulated exocytosis, Recent work (Sc hiavo et al. (1996) Nature 378, 733-736) based on in vitro protein int eractions has raised the possibility that alpha- and beta-SNAPs have d istinct roles in exocytosis. We have examined this possibility by comp aring the activities of recombinant alpha- and beta-SNAPs, Both of the se proteins were able to similarly bind NSF and activate its ATPase ac tivity but to a lesser extent than gamma-SNAP. When introduced into di gitonin-permeabilised chromaffin cells, both alpha- and beta-SNAP stim ulated Ca2+-regulated exocytosis in a MgATP-dependent manner, The dose -response relationships for these proteins were essentially the same a nd addition of both proteins did not lead to any further increase in e xocytosis above that due to each protein alone, We conclude that alpha - and beta-SNAPs are interchangeable isoforms with similar functions i n regulated exocytosis.