Binding of phospholipase C-related but catalytically inactive protein to phosphatidylinositol 4,5-bisphosphate via the PH domain

Abstract

A well-known protein module regulating molecular interactions is the pleckstrin homology (PH) domain whose best-characterised ligand is phosphoinositide. In the present study, we analysed the PH domain from PRIP (phospholipase C-related but catalytically inactive protein, comprising types 1 and 2) regarding phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P 2] binding employing a variety of binding assays. The PH domains prepared from PRIP-1 and -2 showed similar binding profiles to soluble ligands in vitro and showed similar plasma membrane localisation to that of PLC-δ1; however, the PH domain with the N-terminal extension of PRIP-1 but not PRIP-2 showed even distribution throughout the cytoplasm, indicating that the N-terminal extension of PRIP-1 inhibited binding to PtdIns(4,5)P 2 present in the plasma membrane. A chimeric molecule of PLC-δ1 PH domain with the N-terminal extension of PRIP-1 exhibited similar localisation to PRIP-1 PH domain with the N-terminal extension. Binding assay to liposomes containing various concentrations of PtdIns(4,5)P 2 revealed that the PH domain of PLC-δ1 bound steeply to the maximum, even at a concentration of 1.2 mol%, whereas the PH domains from PRIP-1 and -2 bound depending on the concentration up to 5 mol%. We also performed binding experiments using saponin-permeabilised PC12 cells. PH domains from PRIP increased the binding to cells preincubated with the brain cytosol extract in the presence of ATP, during which PtdIns(4,5)P 2 were probably synthesised. The binding of PH domain with the following EF hand motifs showed Ca 2+-dependent binding. These results indicate that the PH domain of PRIP binds to PtdIns(4,5)P 2 present in the plasma membrane, depending on the concentrations of the lipid ligand and Ca 2+, suggesting that PRIP might play physiological roles in events involved in the changes of these parameters, probably including Ins(1,4,5)P 3.