Fig. 5.

Membrane bending and scission. (A) Scaffolds of clathrin and BAR domain proteins can induce membrane bending by changing the spontaneous curvature of the membrane. (B) BAR domains stabilize the tubule neck but can also mediate scission by limiting lipid diffusion and creating friction forces as the tubule is pulled toward the cytoplasm. (C) Steric crowding of bulky domains favors membrane bending if there is an asymmetry of lateral pressure (left); however, the extracellular domains of CCP cargo will also be crowded in the CCP lumen, generating force that opposes invagination (right). The net energy contribution to CME will be determined by the relative sizes and densities of the intracellular and extracellular domains. (D) Dynamin assembles at the membrane tubule neck. Binding of GTP induces the helical oligomer to undergo a conformational change driving constriction, reducing the radius and elongating along the tubule axis. GTP hydrolysis leads to both scission of the membrane neck and disassembly of the dynamin scaffold (not shown).