Acts as a co-chaperone of HSP90AA1 (PubMed:29127155). Activates the ATPase activity of HSP90AA1 leading to increase in its chaperone activity (PubMed:29127155). Competes with the inhibitory co-chaperone FNIP1 for binding to HSP90AA1, thereby providing a reciprocal regulatory mechanism for chaperoning of client proteins (By similarity). Competes with the inhibitory co-chaperone TSC1 for binding to HSP90AA1, thereby providing a reciprocal regulatory mechanism for chaperoning of client proteins (PubMed:29127155). Interacts with HSPCA/HSP90 (By similarity). Interacts with HSP90AA1; the interaction activates HSP90AA1 ATPase activity (PubMed:29127155). Interacts with HSP90AB1 (PubMed:22022502). Interacts with GCH1 (By similarity). Interacts with SRPK1 (By similarity). Interacts with FLCN (By similarity). May transiently interact with the endoplasmic reticulum. By heat shock and treatment with the HSP90 inhibitor 17-demethoxygeldanamycin (17AAG). Phosphorylation at Tyr-223 enhances binding to chaperone HSP90AA1. Belongs to the AHA1 family.