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. Widely expressed with highest levels in kidney. Higher levels occur in the proximal convoluted tubule of strain SHR than strain Wistar Kyoto. Belongs to the cyclophilin-type PPIase family. PPIase B subfamily. It is uncertain whether Met-1 or Met-9 is the initiator.