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The GTPase dynamin has captivated researchers for over two decades, even managing to establish its own research field. Dynamin's allure is partly due to its unusual biochemical properties as well as its essential role in multiple cellular processes, which include the regulation of clathrin-mediated endocytosis and of actin cytoskeleton. On the basis of the classic model, dynamin oligomerization into higher order oligomers such as rings and helices directly executes the final fission reaction in endocytosis, which results in the generation of clathrin-coated vesicles. Dynamin's role in the regulation of actin cytoskeleton is mostly explained by its interactions with a number of actin-binding and -regulating proteins; however, the molecular mechanism of dynamin's action continues to elude us. Recent insights into the mechanism and role of dynamin oligomerization in the regulation of actin polymerization point to a novel role for dynamin oligomerization in the cell., (© 2013 The Authors. Traffic published by John Wiley & Sons Ltd.)

During clathrin-mediated endocytosis, dynamin promotes the formation of clathrin-coated vesicles, but its mode of action is unresolved. In a recent study, Macia and colleagues made use of dynasore, a dynamin-specific inhibitor, to show that dynamin plays a dual role in endocytosis: they confirmed that dynamin is involved in detaching fully formed coated pits from the membrane, and also propose a new role for dynamin earlier in the process at the point of invagination.

During clathrin-mediated endocytosis, the GTPase dynamin promotes formation of clathrin-coated vesicles, but its mode of action is unresolved. We provide evidence that a switch in three functional states of dynamin (dimers, tetramers, rings/spirals) coordinates its GTPase cycle. Dimers exhibit negative cooperativity whereas tetramers exhibit positive cooperativity with respect to GTP. Our study identifies tetramers as the kinetically most stable GTP-bound conformation of dynamin, which is required to promote further assembly into higher order structures such as rings or spirals. In addition, using fluorescence lifetime imaging microscopy, we show that interactions between dynamin and auxilin in cells are GTP-, endocytosis- and tetramer-dependent. Furthermore, we show that the cochaperone activity of auxilin is required for constriction of clathrin-coated pits, the same early step in endocytosis known to be regulated by the lifetime of dynamin:GTP. Together, our findings support the model that the GTP-bound conformation of dynamin tetramers stimulates formation of constricted coated pits at the plasma membrane by regulating the chaperone activity of hsc70/auxilin.

The GTPase dynamin is essential for endocytosis, but its mechanism of action remains uncertain. Structures of its GTPase domain, as well as that of assembled dynamin, have led to major advances in understanding the structural basis of its mode of action. Novel data point more clearly than ever towards a role for this protein in the actin cytoskeleton, mitogen-activated protein kinase signaling and apoptosis, suggesting that dynamin might be a signaling GTPase.

The large GTPase dynamin assembles into higher order structures that are thought to promote endocytosis. Dynamin also regulates the actin cytoskeleton through an unknown, GTPase-dependent mechanism. Here, we identify a highly conserved site in dynamin that binds directly to actin filaments and aligns them into bundles. Point mutations in the actin-binding domain cause aberrant membrane ruffling and defective actin stress fibre formation in cells. Short actin filaments promote dynamin assembly into higher order structures, which in turn efficiently release the actin-capping protein (CP) gelsolin from barbed actin ends in vitro, allowing for elongation of actin filaments. Together, our results support a model in which assembled dynamin, generated through interactions with short actin filaments, promotes actin polymerization via displacement of actin-CPs. [ABSTRACT FROM AUTHOR]

Studies the function of the GTPase dynamin in the regulation of clathrin-mediated endocytosis. Effects of point mutations in stimulated assembly of GTPase activity; Identification of the events in clathrin-coated vesicle formation accelerated by the overexpression of dynamin; Inhibition of membrane fusion.

The GTPase dynamin is essential for clathrin-mediated endocytosis. Numerous new and exciting discoveries regarding dynamin function in vivo and in vitro have led to various models in which dynamin functions directly in membrane fission and the release of clathrin-coated vesicles from the plasma membrane. This would make dynamin unique among GTPases in its ability to act as a mechanochemical enzyme. Here we review the various models and their supporting data. We then discuss new findings that raise doubts as to whether dynamin breaks the paradigm that governs regulatory GTPases. [ABSTRACT FROM AUTHOR]

Presents research which studied the role of dynamin in receptor-mediated endocytosis. Dynamin a GTP-hydrolyzing protein; Dynamin's self-assembly; GTPase activity by dynamin; Dynamin's hydrolysis of GTP; Effects of the overexpression of dynamin mutants; Dynamin not behaving like a force-generating GTPase.

The large GTPase dynamin is required for budding of clathrin-coated vesicles from the plasma membrane, after which the clathrin coat is removed by the chaperone Hsc70 and its cochaperone auxilin. Recent evidence suggests that the GTP-bound form of dynamin may recruit factors that execute the fission reaction. Here, we show that dynamin:GTP binds to Hsc70 and auxilin. We mapped two domains within auxilin that interact with dynamin, and these domains inhibit endocytosis when overexpressed in HeLa cells or when added in a permeable cell assay. The inhibition is not due to impairment of clathrin uncoating or to altered clathrin distribution in cells. Thus, in addition to its requirement for clathrin uncoating, our results show that auxilin also acts during the early steps of clathrin-coated vesicle formation. The data suggest that dynamin regulates the action of molecular chaperones in vesicle budding during endocytosis. [Copyright &y& Elsevier]