PIN1 is a peptidyl-prolyl cis/trans isomerase (PPIase), which specifically binds to phosphoserine-proline or phosphothreonine-proline bonds in mitotic phosphoproteins. Pin1 is a small (18 kDa) protein with two distinct functional domains: an amino-terminal WW domain and a carboxy-terminal PPlase domain. Pin1 interacts with several mitotic phosphoproteins, including Plk1, cdc25C and cdc27, and is thought to act as a phosphorylation-dependent PPlase for these target molecules.
