Peptidyl-prolyl cis-trans isomerase () (PPIase or rotamase) is an enzyme that accelerates protein folding by catalysing the cis-transisomerisation of proline imidic peptide bonds in oligopeptides []. Most characterised PPiases belong to two families, the cyclophilin-type and the the FKBP-type. A third family has been discovered []. So far, the only biochemically characterised member of this family is the Escherichia coli protein parvulin (gene ppiC), a small (92 residues) cytoplasmic enzyme that prefers amino acid residues with hydrophobic side chains like leucine and phenylalanine in the P1 position of the peptides substrates.This entry represents a conserved region that contains a serine which could play a role in the catalytic mechanism of these enzymes. This domain is present in Periplasmic chaperone PpiD that were originally thought to be peptidyl-prolyl isomerases but it was shown later that they lack such activity [].
