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 cyclosporin A (CsA). Belongs to the cyclophilin-type PPIase family. PPIase B subfamily.