Dynamin recruitment and membrane scission at the neck of a clathrin-coated pit.
Bottom Line: The first is associated with coated pit maturation; the second, with fission of the membrane neck of a coated pit.A large fraction of budding coated pits recruit between 26 and 40 dynamins (between 1 and 1.5 helical turns of a dynamin collar) during the recruitment phase associated with neck fission; 26 are enough for coated vesicle release in cells partially depleted of dynamin by RNA interference.We discuss how these results restrict models for the mechanism of dynamin-mediated membrane scission.
Affiliation: Department of Cell Biology, Harvard Medical School, and Cellular and Molecular Medicine Program, Boston Children's Hospital, Boston, MA 02115 Department of Pediatrics, Harvard Medical School, Boston, MA 02115.Show MeSH
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Mentions: Dynamins have an N-terminal GTPase “head,” similar in structure to Ras-like small GTPases, connected to a long, primarily α-helical stalk (Chappie et al., 2009; Chappie and Dyda, 2013; Faelber et al., 2011; Ford et al., 2011). The stalk, which has a membrane-interacting PH domain at its tip, doubles back, so that the C-terminus of the polypeptide chain contacts the head. In solution, dynamin dimerizes readily; the dimers associate into tetramers at higher concentrations. Crystal structures and cryo–electron microscopic (cryo-EM) reconstructions suggest that two sets of dimer contacts are critical for polymer assembly (Chappie et al., 2011). An oblique contact between stalks of two protomers produces an X-shaped dimer, with the GTPase domains projecting away from the midplane of the X. The PH domains are flexibly tethered at the other end of each stalk (Figure 1). GTPase–GTPase contacts generate a second twofold relationship between two of the stalk dimers just described. The two contacts produce a repeating, helical polymer (Figure 1), with the midplane of the X normal to the helix axis. GTP, which binds near the GTPase dimer interface, stabilizes the dimer contact, and formation of the interface greatly increases the rate of nucleotide hydrolysis.
Affiliation: Department of Cell Biology, Harvard Medical School, and Cellular and Molecular Medicine Program, Boston Children's Hospital, Boston, MA 02115 Department of Pediatrics, Harvard Medical School, Boston, MA 02115.