Abstract
The ESCRT pathway mediates a series of important cellular membrane remodeling and fission events, including cytokinetic abscission. During these processes, ESCRT-III family proteins form filaments that appear to constrict membranes and facilitate fission. We have used electron cryomicroscopy to determine the near-atomic resolution structure of helical double-stranded filaments formed by two homologous human ESCRT-III subunits that function in abscission, CHMP1B and IST1. The inner strand comprises interlocking CHMP1B subunits that adopt extended, open conformations, whereas the outer strand comprises closed, compact IST1 subunits. The double-stranded CHMP1B-IST1 filaments can also form constricting conical spirals in which adjacent turns of the spiral interact through a continuum of related but inequivalent electrostatic interactions that allow the spiral to adjust its diameter continuously. We speculate that the ability to form conical spirals allows the filaments to draw membranes together to the point of fission.
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