A number of processes contributing to important cellular functions such as cellular signal transduction, cytoskeletal organization, and membrane trafficking are known to be localized at membrane surfaces of the plasma membrane and organelles. For instance, extracellular signals are often transmitted from activated receptors to peripheral membrane proteins, such heterotrimeric G-proteins, and subsequently amplified and ⁄ or passed to successors by a number of peripheral membrane proteins located at the membrane surface. Because the interface between the aqueous phase and the hydrophobic interior of the membrane provides a unique molecular environment completely different from the homogeneous solution phase environment [1,2], one would expect induction of unique structurefunction relationships for the peripheral membrane The membrane binding affinity of the pleckstrin homology (PH) domain of phospholipase C (PLC)-d1 was investigated using a vesicle coprecipitation assay and the structure of the membrane-associated PH domain was probed using solid-state 13 C NMR spectroscopy. Twenty per cent phosphatidylserine (PS) in the membrane caused a moderate but significant reduction of the membrane binding affinity of the PH domain despite the predicted electrostatic attraction between the PH domain and the head groups of PS. Solid-state NMR spectra of the PH domain bound to the phosphatidylcholine (PC) ⁄ PS ⁄ phosphatidylinositol 4,5-bisphosphate (PIP 2 ) (75 : 20 : 5) vesicle indicated loss of the interaction between the amphipathic a2-helix of the PH domain and the interface region of the membrane which was previously reported for the PH domain bound to PC ⁄ PIP 2 (95 : 5) vesicles. Characteristic local conformations in the vicinity of Ala88 and Ala112 induced by the hydrophobic interaction between the a2-helix and the membrane interface were lost in the structure of the PH domain at the surface of the PC ⁄ PS ⁄ PIP 2 vesicle, and consequently the structure becomes identical to the solution structure of the PH domain bound to d-myo-inositol 1,4,5-trisphosphate. These local structural changes reduce the membrane binding affinity of the PH domain. The effects of PS on the PH domain were reversed by NaCl and MgCl 2 , suggesting that the effects are caused by electrostatic interaction between the protein and PS. These results generally suggest that the structure and function relationships among PLCs and other peripheral membrane proteins that have similar PH domains would be affected by the local lipid composition of membranes.Abbreviations DD-MAS, single pulse excitation dipolar decoupled-magic angle spinning; GST, glutathione-S-transferase; IP 3 , D-myo-inositol 1,4,5-trisphosphate; PC, phosphatidylcholine; PH domain, pleckstrin homology domain; PIP 2 , phosphatidylinositol