Phosphorylation of Rabphilin-3A by calmodulin-dependent protein kinase II.

Rabphilin-3A is a putative target protein for Rab3A small GTP-binding protein which is implicated in neurotransmitter release. We have examined here whether Rabphilin-3A is phosphorylated by calmodulin-dependent protein kinase II (CaMKII). Recombinant Rabphilin-3A was phosphorylated by CaMKII purified from rat brain. Two moles of phosphate were maximally incorporated into one mole of Rabphilin-3A. The phosphorylation sites were Ser34, Thr205, Thr209, and Thr537. These results suggest that the CaMKII-catalyzed phosphorylation of Rabphilin-3A may modulate neurotransmitter release.