Heat shock protein 105 kDa?is a?protein?that in humans is encoded by the?HSPH1?gene. Prevents the aggregation of denatured proteins in cells under severe stress, on which the ATP levels decrease markedly. Inhibits HSPA8/HSC70 ATPase and chaperone activities. Highly expressed in testis. Present at lower levels in most brain regions, except cerebellum. Overexpressed in cancer cells. Phosphorylation on Ser-509 may be important for regulation of the HSPA8/HSC70 chaperone activity.