PHOSPHATIDYLINOSITOL (4,5)-BISPHOSPHATE-DEPENDENT ACTIVATION OF DYNAMIN-I AND DYNAMIN-II LACKING THE PROLINE ARGININE-RICH DOMAINS/

Dynamins comprise a family of GTPases that participate in the early st ages of endocytosis. The GTPase activity of neuronal specific dynamin I is stimulated by microtubules, negatively charged phospholipid vesic les, and Src homology 3-containing proteins, including Grb2. These act ivators were previously shown to bind to a proline/arginine-rich domai n (PRD) in the carboxyl-terminal region of the enzyme. Dynamin II, whi ch is ubiquitously expressed, had not been purified or characterized p reviously. In this study, the enzymatic properties of rat dynamin II a nd of D746, a dynamin II truncation mutant lacking the PRD, have been characterized. Dynamin II has a higher basal activity than dynamin I, but the two types of dynamin are stimulated similarly by microtubules, Grb2, and phospholipids. D746 is not activated by microtubules or Grb 2, highlighting the significance of the PRD for these interactions, bu t it is activated by phospholipid vesicles containing phosphatidylseri ne or phosphatidylinositol-4,5-bisphosphate. Moreover, in contrast to previous reports, the PRD appears not to be required for phospholipid- stimulated self-assembly of dynamin, which is a key element in the reg ulation of its activity. Similar results were obtained with bovine bra in dynamin I that had been subjected to limited proteolytic digestion to remove the PRD. Our data highlight the potential involvement of dyn amin pleckstrin homology domains in the regulation of GTPase activity by phospholipids.