2.3 Å Resolution Cryo-EM Structure of Human p97 and Mechanism of Allosteric Inhibition
The protein p97 is an AAA adenosine triphosphatase (ATPase) that uses energy from ATP hydrolysis to regulate substrates involved in intracellular protein quality control. Its role in this central process makes it a target for cancer chemotherapy. We used cryo-electron microscopy to determine high-resolution structures for multiple conformational states of this dynamic macromolecular machine. They also determined the structure of the ADP-bound state bound to an inhibitor. The structures give insight into nucleotide-driven structural changes that drive function and show how inhibitor binding prevents these conformational changes.
p97 is a hexameric AAA+ adenosine triphosphatase (ATPase) that is an attractive target for cancer drug development. We report cryo-electron microscopy (cryo-EM) structures for adenosine diphosphate (ADP)-bound, full-length, hexameric wild-type p97 in the presence and absence of an allosteric inhibitor at resolutions of 2.3 and 2.4 angstroms, respectively. We also report cryo-EM structures (at resolutions of ~3.3, 3.2, and 3.3 angstroms, respectively) for three distinct, coexisting functional states of p97 with occupancies of zero, one, or two molecules of adenosine 5'-O-(3-thiotriphosphate) (ATPγS) per protomer. A large corkscrew-like change in molecular architecture, coupled with upward displacement of the N-terminal domain, is observed only when ATPγS is bound to both the D1 and D2 domains of the protomer. These cryo-EM structures establish the sequence of nucleotide-driven structural changes in p97 at atomic resolution. They also enable elucidation of the binding mode of an allosteric small-molecule inhibitor to p97 and illustrate how inhibitor binding at the interface between the D1 and D2 domains prevents propagation of the conformational changes necessary for p97 function.