Keeps in an inactive conformation TGFBR1, the TGF-beta type I serine/threonine kinase receptor, preventing TGF-beta receptor activation in absence of ligand. May modulate the RYR1 calcium channel activity. 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. Interacts with TGFBR1; prevents TGFBR1 phosphorylation by TGFBR2 and stabilizes it in the inactive conformation. Interacts with ACVR1B and SMAD7 (By similarity). Identified in a complex composed of RYR1, PDE4D, PKA, FKBP1A and protein phosphatase 1 (PP1) (By similarity). Interacts directly with RYR2 and RYR3. Interacts with GLMN; rapamycin and FK506 abolish the interaction with GLMN in a dose dependent manner (By similarity). Interacts directly with RYR1 (By similarity). Belongs to the FKBP-type PPIase family. FKBP1 subfamily. Was originally thought to be protein kinase C inhibitor 2 (PKCI-2 or 12 kDa inhibitor of protein kinase C). Later, was shown experimentally not to inhibit protein kinase C (PubMed:1868545, PubMed:1710782).