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: The radius of the membrane tubule within a GMPPCP dynamin sheath is ∼5 nm (from the axis to the center of the bilayer; Chappie et al., 2011). Spontaneous hemifission is believed to require a radius of ∼3 nm (Kozlovsky and Kozlov, 2003). Conformational changes in a dynamin collar could produce such a contraction either by a rotation of the stalks toward a more radial orientation, forcing the PH domains inward while leaving the helical parameters of the outer layer more or less unchanged, or by a decrease in the number of dynamins per turn of the helix, reducing both its outer and inner diameter without changing the radial disposition of the stalks. These two alternatives correspond roughly to the models proposed by Chappie et al. (2011) and by Smirnova et al. (1999) and Faelber et al. (2011). The former is, in its simplest form, an isotropic squeeze (Figure 10A); the latter, a circumferential twist (Figure 10B and Supplemental Movies S1–S3). The isotropic contraction model requires nearly a full turn of paired GTPase domains—that is, nearly two turns of the basic helix. The circumferential twist model requires simply that the assembly reach a state in which one or more pairs of GTPase domains interact. Our data appear to favor the latter picture.
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.