RESUMEN
Dynamin is a GTPase thought to play a role in endocytosis based on genetic analysis of its homolog in Drosophila melanogaster shibire. Previous studies have stressed an in vitro association with microtubules, though additional evidence suggests that dynamin associates with membranous organelles. In an analysis of the enzymatic and membrane binding properties of dynamin, we have found that the acidic phospholipids, phosphatidylserine, phosphatidylglycerol, and phosphatidylinositol, are able to stimulate GTP hydrolysis in a manner similar to activation previously shown with microtubules. A neutral phospholipid, phosphatidylcholine, had no effect on dynamin GTPase. Activation of dynamin was biphasic, with a decrease in activity back to basal levels with increased concentrations of either microtubules or liposomes. A comparison between GTPase stimulation induced by microtubules and that by phospholipids suggests that ionic interactions between the basic C-terminal domain of dynamin and the negatively charged microtubule or phospholipid head group are important. In support of this, GTPase stimulation by these agents in combination was not additive. A salt-extracted membrane fraction from brain tissue also activated dynamin GTPase, though to a lower extent than pure phospholipids. These results suggest that membrane components could be responsible for some aspects of the regulation of dynamin function in vivo.