Vacuolar Protein Sorting: Two Different Functional States of the AAA-ATPase Vps4p

The vacuolar protein sorting (Vps) pathway, in which Vps4 class I AAA-ATPases play a central role, regulates growth factor receptors, immune response, and developmental signaling, and participates in tumor suppression, apoptosis, and retrovirus budding. We present the first atomic structure of the nucleotide-free yeast His6ΔNVps4p dimer and its AMPPNP (5′-adenylyl-β,γ-imidodiphosphate)-bound tetradecamer, derived from a cryo electron microscopy map. Vps4p dimers form two distinct heptameric rings and accommodate AAA cassettes in a head-to-head—not in a head-to-tail—fashion as in class II AAA-ATPases. Our model suggests a mechanism for disassembling ESCRT (endosomal sorting complex required for transport) complexes by movements of substrate-binding domains located at the periphery of the tetradecamer during ATP hydrolysis in one ring, followed by translocation through the central pore and ATP hydrolysis in the second ring.