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Altered cofactor regulation with disease-associated p97/VCP mutations

Significance Age-associated degenerative diseases have similar pathogenic mechanisms related to defects in protein homeostasis. p97/VCP (valosin-containing protein) is essential for coordinating protein degradation and is mutated in a multisystem degenerative disease that affects the central nervous system, muscle, and bone. p97/VCP is an enzyme in the AAA ATPases (ATPases associated with diverse cellular activities) family, which takes apart ATP and uses this energy to perform pivotal functions. We found that p97/VCP cofactors control its enzymatic activity. p97/VCP disease mutants behave abnormally due to lack of appropriate control by these cofactors. Correcting the function of the disease-associated proteins may be a desirable approach to developing safe treatment for fatal degenerative diseases. The next steps are to screen and characterize large panels of compounds to identify potential drugs that may correct the malfunction. Dominant mutations in p97/VCP (valosin-containing protein) cause a rare multisystem degenerative disease with varied phenotypes that include inclusion body myopathy, Paget’s disease of bone, frontotemporal dementia, and amyotrophic lateral sclerosis. p97 disease mutants have altered N-domain conformations, elevated ATPase activity, and altered cofactor association. We have now discovered a previously unidentified disease-relevant functional property of p97 by identifying how the cofactors p37 and p47 regulate p97 ATPase activity. We define p37 as, to our knowledge, the first known p97-activating cofactor, which enhances the catalytic efficiency (kcat/Km) of p97 by 11-fold. Whereas both p37 and p47 decrease the Km of ATP in p97, p37 increases the kcat of p97. In contrast, regulation by p47 is biphasic, with decreased kcat at low levels but increased kcat at higher levels. By deleting a region of p47 that lacks homology to p37 (amino acids 69–92), we changed p47 from an inhibitory cofactor to an activating cofactor, similar to p37. Our data suggest that cofactors regulate p97 ATPase activity by binding to the N domain. Induced conformation changes affect ADP/ATP binding at the D1 domain, which in turn controls ATPase cycling. Most importantly, we found that the D2 domain of disease mutants failed to be activated by p37 or p47. Our results show that cofactors play a critical role in controlling p97 ATPase activity, and suggest that lack of cofactor-regulated communication may contribute to p97-associated disease pathogenesis.