Dynamin is a GTP-hydrolysing protein that is an essential participant in clathrin-mediated endocytosis by cells. It self-assembles into 'collars' in vitro which also form in vivo at the necks of invaginated coated pits. This self-assembly stimulates dynamin's GTPase activity and it has been proposed that dynamin hydrolyses GTP In order to generate the force needed to sever vesicles from the plasma membrane. A mechanism is now described in which self-assembly of dynamin Is coordinated by a domain of dynamin with a GTPase- activating function. Unexpectedly, when dynamin mutants defective In self- assembly-stimulated GTPase activity are overexpressed, receptor-mediated endocytosis is accelerated. The results Indicate that dynamin, like other members of the GTPase superfamily, functions as a molecular regulator in receptor-mediated endocytosis, rather than as a force-generating GTPase.
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