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. Involved in the inhibition of viral infection by influenza A viruses (IAV) (PubMed:28169297). {ECO:0000269|PubMed:12510191, ECO:0000269|PubMed:15757646, ECO:0000269|PubMed:16176796, ECO:0000269|PubMed:28169297}. This is the function of FKBP8 (FKBP prolyl isomerase 8, Ensembl gene identifier ENSG00000105701).