Calcium-triggered membrane fusion proceeds independently of specific presynaptic proteins. Academic Article uri icon


  • Complexes of specific presynaptic proteins have been hypothesized to drive or catalyze the membrane fusion steps of exocytosis. Here we use a stage-specific preparation to test the roles of SNAREs, synaptotagmin, and SNARE-binding proteins in the mechanism of Ca2+-triggered membrane fusion. Excess exogenous proteins, sufficient to block SNARE interactions, did not inhibit either the Ca2+ sensitivity, extent, or kinetics of fusion. In contrast, despite a limited effect on SNARE and synaptotagmin densities, treatments with high doses of chymotrypsin markedly inhibited fusion. Conversely, low doses of chymotrypsin had no effect on the Ca2+ sensitivity or extent of fusion but did alter the kinetic profile, indicating a more direct involvement of other proteins in the triggered fusion pathway. SNAREs, synaptotagmin, and their immediate binding partners are critical to exocytosis at a stage other than membrane fusion, although they may still influence the triggered steps.

published proceedings

  • J Biol Chem

author list (cited authors)

  • Szule, J. A., Jarvis, S. E., Hibbert, J. E., Spafford, J. D., Braun, J., Zamponi, G. W., Wessel, G. M., & Coorssen, J. R.

citation count

  • 44

complete list of authors

  • Szule, Joseph A||Jarvis, Scott E||Hibbert, Julie E||Spafford, J David||Braun, Janice EA||Zamponi, Gerald W||Wessel, Gary M||Coorssen, Jens R

publication date

  • July 2003