Dynamic Regulation of p97 ATPase Activity by p37 and p47 is Impaired in Pathogenic p97 IBMPFD/ALS Mutants

Mutations in p97, a major cytosolic AAA (ATPases associated with a variety of cellular activities) chaperone, cause inclusion body myopathy associated with Paget's disease of the bone and frontotemporal dementia (IBMPFD) and amyotrophic lateral sclerosis (ALS).Several IBMPFD‐linked p97 mutants have been observed with an altered N‐domain conformation which is further supported by atypical p97 cofactor association in cells. Our study examines how cofactors p37 and p47 regulate p97 ATPase activity of WT and IBMPFD/ALS mutants of p97 and identifies a new functional property of p97. We establish p37 as the first known p97‐activating cofactor, which enhances the catalytic efficiency (k cat /K m ) of WT p97 by 11‐fold. We conclusively demonstrate that regulation by p47 occurs biphasically in a concentration‐dependent manner. Additionally, we identify amino acids 69 to 92 of p47 to be responsible for its inhibitory effect on p97. Removal of this region changes p47 from an inhibitory cofactor to an activating cofactor that is structurally and functionally similar to p37. We find that IBMPFD p97 mutants lack a biphasic effect in the presence of WT p47, cannot be activated by WT p37 or a p37 mimic (Δ69‐92 p47).Our results suggest a general model for cofactor‐regulated p97 ATPase activity: a cofactor binds to the N‐domain of WT p97 and induces conformational changes that regulate ADP/ATP binding to the D1 domain, which in turn controls the D1 and D2 ATPase cycles.Above all, our results support the critical role of the p97 cofactor in regulating its ATPase activity and suggest that lack of cofactor‐regulated communication may contribute to pathogenesis of IBMFPD/ALS in individuals with p97 mutations.