Constitutively inactive PPiase, which becomes active when bound to calmodulin and calcium. Seems to act as a chaperone for BCL2, targets it to the mitochondria and modulates its phosphorylation state. The BCL2/FKBP8/calmodulin/calcium complex probably interferes with the binding of BCL2 to its targets. The active form of FKBP8 may therefore play a role in the regulation of apoptosis (By similarity). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Homomultimers or heteromultimers (Potential). Forms heterodimer with calmodulin. When activated by calmodulin and calcium, interacts with the BH4 domain of BCL2 and weakly with BCLX isoform Bcl-X(L). Does not bind and inhibit calcineurin. Interacts with ZFYVE27; may negatively regulate ZFYVE27 phosphorylation (By similarity). Ubiquitinated by PRKN during mitophagy, leading to its degradation and enhancement of mitophagy. Deubiquitinated by USP30. Binds the immunosuppressant FK506 only in its calmodulin/calcium activated form.