PHOSPHORYLATION OF DYNAMIN-I AND SYNAPTIC-VESICLE RECYCLING

In nerve terminals, neurotransmitters are packaged in synaptic vesicle s, and released by exocytosis. Empty synaptic vesicles are rapidly rec ycled for reuse by endocytosis. Much progress has been made in identif ying the proteins involved in synaptic-vesicle trafficking, but the me chanism and regulation of endocytosis have largely remained an enigma. One approach to defining regulatory proteins that might be involved i s to study stimulus-dependent phosphorylation events in nerve terminal s. This has led to the identification of dephosphin, which is quantita tively dephosphorylated by nerve-terminal depolarization. Sequencing r eveals that dephosphin is identical with dynamin I, a GTP-binding prot ein that functions in endocytosis. Phosphorylation and dephosphorylati on of nerve-terminal dynamin I/dephosphin regulates its intrinsic GTPa se activity in parallel with regulation of synaptic-vesicle recycling. Therefore, phosphorylation and dephosphorylation of dynamin I might p rovide a Ca2+-dependent switch for endocytosis in the synaptic-vesicle pathway.