Synergistic activation of dynamin GTPase by Grb2 and phosphoinositides

Hydrolysis of GTP by dynamin is essential for budding clathrin-coated vesicles from the plasma membrane. Two distinct domains of dynamin are implicated in the interactions with dynamin GTPase activators. Microtubules and Grb2 bind to the carboxyl-terminal proline/arginine-rich domain (PRD), whereas phosphoinositides bind to the pleckstrin homology (PH) domain. In this study we tested the effect of different phosphoinositides on dynamin GTPase activity and found that the best activator is phosphatidylinositol 4,5-bisphosphate followed by 1-O-(1,2-di-O-palmitoyl-sn-glycerol-3- benzyloxyphosphoryl)-D-myo-inositol 3,4,5-triphosphate. Phosphatidylinositol 4-phosphate was a weak activator and phosphatidylinositol 3,4-bisphosphate did not activate GTPase at all. We then addressed the question of whether both domains of dynamin, PRD and PH, can be engaged simultaneously, and determined the effects of dual occupancy on dynamin GTPase activity. We found that Grb2 and phosphatidylinositol 4,5-bisphosphate together increased the dynamin GTPase activity up to 4-fold higher than that obtained by these activators tested separately, and also reduced the dynamin concentration required for half-maximal activities by 3-fold. These results indicate that both stimulators can bind to dynamin simultaneously resulting in superactivation of dynamin GTPase activity. We propose that SH3-containing proteins such as Grb2 bind to the dynamin PRD to target it to clathrin- coated pits and prime it for superactivation by phosphoinositides.