Has the potential to contribute to the immunosuppressive and toxic effects of FK506 and rapamycin. PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Inhibited by both FK506 and rapamycin. Identified in a complex composed of RYR2, FKBP1B, PKA catalytic subunit, PRKAR2A, AKAP6, and the protein phosphatases PP2A and PP1. Interacts directly with RYR2. Detected in heart muscle (at protein level). Isoform 1 and isoform 2 are ubiquitous with highest levels in brain and thymus. Belongs to the FKBP-type PPIase family. FKBP1 subfamily.