Immunophilin protein with PPIase and co-chaperone activities (By similarity). Component of unliganded steroid receptors heterocomplexes through interaction with heat-shock protein 90 (HSP90). May play a role in the intracellular trafficking of heterooligomeric forms of steroid hormone receptors between cytoplasm and nuclear compartments (By similarity). The isomerase activity controls neuronal growth cones via regulation of TRPC1 channel opening. Acts also as a regulator of microtubule dynamics by inhibiting MAPT/TAU ability to promote microtubule assembly.
The PPIase activity is mainly due to the fisrt PPIase FKBP-type domain (1-138 AA). The C-terminal region (AA 375-458) is required to prevent tubulin polymerization. The chaperone activity resides in the C-terminal region, mainly between amino acids 264 and 400.
Phosphorylation by CK2 results in loss of HSP90 binding activity (By similarity). Phosphorylated upon DNA damage, probably by ATM or ATR.