Dynamins comprise a family of 100 kD GTPases involved in endocytosis. Three dynamin genes and alternate splice variants of each exist. Dephosphorylation of the neuron-specific dynamin I by the calcium/calmodulin-dependent Ser/Thr phosphatase calcineurin has been shown, in vitro, to inhibit its GTPase activity. To date, only limited data have been reported distinguishing the functions of the several dynamin genes and of their alternative splice products. Our studies were designed to examine the interaction of calcineurin with dynamin isoforms. We find that dynamin from PC 12 cell lysates binds specifically to calcineurin immobilized on calcium-activated calmodulin-sepharose beads. Using dynamin isoform-specific antibodies, we find that the bound protein includes dynamin Ib, but not the ubiquitous dynamin H. Overexpression experiments in COS-7 cells demonstrate specific binding of dynamin Ib, but not of dynamin la or of dynamin U, to calcineurin. Furthermore, using a series of truncation mutants, we show that the extreme carboxy terminus of dynamin Ib, which is unique to this isoform, is required for binding. It is tempting to speculate that differential binding of calcineurin to distinct isoforms of dynamin I may play a role in regulated synaptic vesicle recycling.
|Published - 1998