SPECIFIC ROLE FOR THE PH DOMAIN OF DYNAMIN-1 IN THE REGULATION OF RAPID ENDOCYTOSIS IN ADRENAL CHROMAFFIN CELLS

Dynamin plays a key role in the scission event common to various types of endocytosis. We demonstrate that the pleckstrin homology (PH) doma in of dynamin-1 is critical in the process of rapid endocytosis (RE) i n chromaffin cells. Introduction of this isolated PH domain into cells at concentrations as low as 1 mu M completely suppressed RE. PH domai ns from other proteins, including that from the closely related dynami n-2, were ineffective as inhibitors, even at high concentrations. Muta tional studies indicated that a pair of isoform-specific amino acids, located in a variable loop between the first two beta-strands, account ed for the differential effect of the two dynamin PH domains. Switchin g these amino acids in the dynamin-2 PH domain to the equivalent resid ues in dynamin-1 (SL-->GI) generated a molecule that blocked RE. Thus, the PH domain of dynamin-1 is essential for RE and exhibits a precise molecular selectivity, As chromaffin cells express both dynamin-1 and -2, we speculate that different isoforms of dynamin may regulate dist inct endocytotic processes and that the PH domain contributes to this specificity.