Structure and function of PH domain.

The PH domain is a protein module of approximately 120 amino acid residues founded in many proteins involved in signal transduction. The PH domains are similar to each other in their three-dimensional structures, and the major structure difference among them lies in the three variable loops in the structures. The PH domain is electrostatically-polarized and the variable loops are on the positively-charged surface, which may serve as a ligand-binding surface. So far, it has been found that PH domains can interact with the beta gamma-subunits of G protein (G beta gamma), protein kinase C (PKC) and phosphatidylinositol-4, 5-bisphosphate ( PIP(2) or inositol-1, 4, 5-trisphosphate (IP(3))). All these implied that PH domain might play an important role in the interaction between the signaling molecules and help to form the signal transduction network.