Structural basis of protein translocation by the AAA ATPase Vps4

The hexameric AAA ATPase Vps4 drives membrane fission by remodeling and disassembling ESCRT-III filaments.  We have determined a 3.2 Å cryo-EM structure of Vps4 bound to an ESCRT-III peptide, which binds the central Vps4 pore in a beta-strand conformation whose helical symmetry matches that of the five Vps4 subunits it contacts directly.  Consequently, adjacent Vps4 subunits make equivalent interactions with successive dipeptides of the substrate through two classes of side chain binding pocket that are formed primarily by Vps4 pore loop 1.  These pockets accommodate a wide range of residue identities, while main chain hydrogen bonds help dictate the substrate-binding orientation.  The structure supports a “conveyor belt” model of translocation in which ATP binding allows a Vps4 subunit to join the growing end of the helix and engage the substrate, while hydrolysis and release promotes disassembly at the lagging end.  Superposition with structures of other AAA ATPases that translocate proteins suggest that many members of this family utilize equivalent mechanisms.