Catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides (PubMed:11690648). Plays a role in protein folding, transport and assembly (PubMed:11690648). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Interacts with snwA. Belongs to the cyclophilin-type PPIase family.