A conserved histidine in human DNLZ/HEP is required for stimulation of HSPA9 ATPase activity

► Human DNLZ regulates HSPA9 solubility and ATPase activity. ► A DNLZ-H107A mutant is impaired in its binding to nucleotide-free HSPA9. ► A DNLZ-H107A mutant does not stimulate HSPA9 ATPase activity. ► A DNLZ-H107A mutant enhances the solubility of recombinant HSPA9. ► A conserved histidine (His107) is critical for DNLZ regulation of folded HSPA9.