Synhibin: A new calcium-dependent membrane-binding protein that inhibits synexin-induced chromaffin granule aggregation and fusion

We report the isolation and purification of synhibin, a new M_r 68000 protein, which inhibits synexin. Synexin mediates Ca²⁺-dependent chromaffin granule aggregation and fusion, processes perhaps important during exocytosis. Our data indicate that synhibin action involves competition with synexin for a site on the chromaffin granule membrane involved in membrane contact. Synhibin may thus be an important intracellular regulator of synexin action during secretion.