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 (By similarity). Interacts directly with RYR2. Detected in heart muscle (at protein level). Ubiquitous. Belongs to the FKBP-type PPIase family. FKBP1 subfamily. Has been suggested to play a role in the regulation of RYR2 channel activity and thereby contribute to the regulation of excitation-contraction coupling in cardiac muscle. According to PubMed:20431056, the amount of FKBP1B in rat heart is much lower than that of RYR2, suggesting that FKBP1B can play only a minor role in the regulation of RYR2 channel activity.