Synaptotagmin regulation of coated pit assembly.

Synaptotagmins bind clathrin AP-2 with high affinity via their second C(2) domain, which indicates they are involved in coated pit function. We now report that expression of synaptotagmins lacking either the second C(2) domain or the entire cytoplasmic region potently inhibit endocytosis. Inhibition was dependent on two intramembrane cysteine residues that were found to be essential for synaptotagmin oligomerization. Cells expressing the wild-type, but not the mutant, truncated synaptotagmin fragment had a reduced number of clathrin-coated pits. These results suggest that the formation of synaptotagmin multimers is an important step in the regulation of coated pit assembly.