Selective protein-lipid interactions at membrane surfaces: a deuterium and phosphorus nuclear magnetic resonance study of the association of myelin basic protein with the bilayer head groups of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol

Abstract

Basic protein from bovine spinal cord was recon- stituted into bilayers of 1,2-dimyristoyl-sn-glycero-3- phosphocholine, 1,2-dimyristoyl-sn-glycero-3-phospho-ruc- glycerol, and equimolar mixtures of both phospholipids at various protein concentrations up to 58 wt %. The lipids were selectively deuterated at all positions in their polar head groups, the motional rate and amplitude of which were characterized by deuterium and phosphorus-3 1 nuclear magnetic resonance (NMR). Basic protein, which binds peripherally to mem- branes, did not perturb any part of the head groups in phos- phatidylcholine bilayers in such a way as to induce any sig- nificant changes in the NMR spectra. However, basic protein induced large effects on the phosphorus-3 1 and the deuterium NMR spectra of bilayers of dimyristoylphosphatidylglycerol. When compared to those of pure phosphatidylglycerol bilayers at 35 OC, the measured quadrupole splittings decreased by 36%, 28%, and 50% for the a-CD2, P-CD, and 7-CD2 glycerol segments, respectively, and the phosphorus-3 1 chemical shift anisotropy (CSA) was reduced by 34% from -39 to -25 ppm by the addition of 50 wt 7% of basic protein. Deuterium spin-lattice relaxation times T1 for the p-CD and the 7-CD2 segments decreased only slightly after the addition of basic protein. These results indicate that basic protein interacts with the acidic polar head group of phosphatidylglycerol, affecting its orientation or amplitude of motion, as well as its rate of Investigations of lipid-protein interactions in reconstituted model membranes by NMR' or ESR spin-label methods have concentrated predominantly on the characterization of the motion of lipid fatty acyl chains with the hydrophobic surface of integral membrane proteins (Marsh & Watts, 1982; Rice et al., 1979; Oldfield et al., 1978; Seelig et al., 1981). Both magnetic resonance approaches are restricted to giving localized molecular information about the environment close to the site of probe attachment, and 2H NMR spectroscopy is in principle the more versatile approach in that deuterium can substitute for protons at many specific positions in a phospholipid to give information about almost any part of the molecule. Although both methods have their own virtues and strengths in their applicability and motional time scales (Watts, 1981), 2H NMR of specifically deuterated lipids is particularly