Peptidyl-Prolyl Cis-Trans Isomerase D (PPID) belongs to the cyclophilin-type PPIase family and PPIase D subfamily. PPID is widely expressed and it contains one PPIase cyclophilin-type domain and three TPR repeats. PPID catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerates the folding of proteins. PPID can bind to the immunosuppressant cyclosporine A and is known that its overexpression suppresses the apoptosis in cancer cells.