Exploiting conformational plasticity in the AAA+ protein VCP/p97 to modify function.

p97/VCP, a member of the AAA+ (ATPases associated with diverse cellular activities) family of proteins, is implicated in the etiology of a group of degenerative diseases affecting bone and muscle tissue as well as the central nervous system. Methyl-TROSY-based NMR studies have previously revealed how disease-causing mutations deregulate a subtle dynamic conformational equilibrium involving the N-terminal domain (NTD) with implications for the binding of certain adaptors, providing insight into how disease mutations lead to abnormal function. Herein the conformational plasticity of the p97 system is explored in an attempt to identify hotspots that can serve as targets for restoring function in disease mutants by shifting the position of the NTD back to its wild-type location. Although p97 is overall robust with respect to extensive mutagenesis throughout the protein involving conservative substitutions of hydrophobic residues, key positions have been identified that alter the NTD equilibrium; these lie in specific regions that localize to the interface between the NTD and the D1 nucleotide-binding domain of the complex. Notably, for a severe disease mutant involving an R155C substitution the NTD equilibrium can be shifted back to its wild-type position by mutation at a secondary site with restoration of wild-type two-pronged binding of the UBXD1 adaptor protein that is impaired in disease; this underlies the potential for recovering function by targeting p97 disease mutants with drug molecules.