May catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides (PubMed:8694762). May play a role in the protein folding, transport and assembly (PubMed:8694762). [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Belongs to the cyclophilin-type PPIase family.