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). Interacts with DYM. Interacts with CALR, CLGN and CANX. Part of a large chaperone multiprotein complex comprising DNAJB11, HSP90B1, HSPA5, HYOU, PDIA2, PDIA4, PDIA6, PPIB, SDF2L1, UGGT1 and very small amounts of ERP29, but not, or at very low levels, CALR nor CANX (PubMed:12475965). (Microbial infection) Interacts with measles virus nucleoprotein. (Microbial infection). Identified by mass spectrometry in melanosome fractions from stage I to stage IV (PubMed:17081065). The disease is caused by variants affecting the gene represented in this entry. Belongs to the cyclophilin-type PPIase family. PPIase B subfamily. It is uncertain whether Met-1 or Met-9 is the initiator. Peptidyl-prolyl cis-trans isomerase B (PPIB)