DYNAMIN GTPASE REGULATED BY PROTEIN-KINASE-C PHOSPHORYLATION IN NERVE-TERMINALS

DYNAMIN is a microtubule-binding protein with a microtubule-activated GTPase activity1-3. The gene encoding dynamin is mutated in shibire4,5 , a Drosophila mutant defective in endocytosis in nerve terminals and other cells6-9. These observations place dynamin into two distinct fun ctional contexts, suggesting roles in microtubule-based motility or in endocytosis. We report here that dynamin is identical to the neuronal phosphoprotein dephosphin (P96), originally identified by its stimulu s-dependent dephosphorylation in nerve terminals10-13. Dynamin is a pr otein doublet of M(r) 94 and 96K arising by alternative splicing of it s primary transcript. In the nerve terminal, both forms of dynamin are phosphorylated by protein kinase C (PKC) and are quantitatively depho sphorylated on excitation. In vitro, dynamin is also phosphorylated by casein kinase II which inhibits PKC phosphorylation. Phosphorylation by PKC but not by casein kinase II enhances the GTPase activity of dyn amin 12-fold. The dynamins are therefore a group of nerve terminal pho sphoproteins whose GTPase is regulated by phosphorylation in parallel with synaptic vesicle recycling. The regulation of dynamin GTPase coul d serve as the trigger for the rapid endocytosis of synaptic vesicles after exocytosis.