Dual function of protein phosphatase 5 (PPP5C): An emerging therapeutic target for drug discovery.

Phosphorylation of proteins is reversibly controlled by the kinases and phosphatases in many posttranslational regulation patterns. Protein phosphatase 5 (PPP5C) is a serine/threonine protein phosphatase showing dual function by simultaneously exerting dephosphorylation and co-chaperone functions. Due to this special role, PPP5C was found to participate in many signal transductions related to various diseases. Abnormal expression of PPP5C results in cancers, obesity, and Alzheimer's disease, making it a potential drug target. However, the design of small molecules targeting PPP5C is struggling due to its special monomeric enzyme form and low basal activity by a self-inhibition mechanism. Through realizing the PPP5C's dual function as phosphatase and co-chaperone, more and more small molecules were found to regulate PPP5C with a different mechanism. This review aims to provide insights into PPP5C's dual function from structure to function, which could provide efficient design strategies for small molecules targeting PPP5C as therapeutic candidates.