PPIase that catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and may therefore assist protein folding. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Inhibited by cyclosporin A (CsA). Expressed in kidney, skeletal muscle, pancreas, heart, lung, liver and to a lower extent in brain. Belongs to the cyclophilin-type PPIase family.