PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides. Binds to ligand-free TGF beta type I receptor, from which it is released upon a ligand-induced, type II receptor mediated phosphorylation of the type I receptor. Binding is inhibitory to the signaling pathways of the TGF beta family ligands. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Belongs to the FKBP-type PPIase family. FKBP1 subfamily.