Influence of membrane curvature on the structure of the membrane-associated pleckstrin homology domain of phospholipase C-δ1

The effects of geometric properties of membranes on the structure of the phospholipase C-δ1 (PLC-δ1) pleckstrin homology (PH) domain were investigated using solid state 13C NMR spectroscopy. Conformations of the PLC-δ1 PH domain at the surfaces of multilamellar vesicles (MLV), small unilamellar vesicles (SUV), and micelles were examined to evaluate the effects of membrane curvature on the PH domain. An increase in curvature of the water–hydrophobic layer interface hinders membrane-penetration of the amphipathic α2-helix of the PH domain that assists the membrane-association of the PH domain dominated by the phosphatidylinositol 4,5-bisphosphate (PIP2) specific lipid binding site. The solid state 13C NMR signal of Ala88 located at the α2-helix indicates that the conformation of the α2-helix at the micelle surface is similar to the solution conformation and significantly different from those at the MLV and SUV surfaces which were characterized by membrane-penetration and re-orientation. The signal of Ala112 which flanks the C-terminus of the β5/β6 loop that includes the α2-helix, showed downfield displacement with decrease in the interface curvature of the micelles, SUV and MLV. This reveals that the conformation of the C-terminus of the β5/β6 loop connecting the β-sandwich core containing the PIP2 binding site and the amphipathic α2-helix is sensitive to alterations of the curvature of lipid bilayer surface. It is likely that these alterations in the conformation of the PLC-δ1 PH domain contribute to the regulatory mechanisms of the intracellular localization of PLC-δ1 in a manner dependent upon the structure of the molecular complex containing PIP2.