title: Effect of bacteriorhodopsin on the orientation of the headgroup of 1,2-dimyristoyl-sn-glycero-3-phosphocholine in bilayers: a 31P- and 2H-NMR study.
abstract: Bacteriorhodopsin (BR), purified from the halophilic bacterium, Halobacterium halobium, has been separated from the endogenous purple membrane lipids and reconstituted by detergent dialysis into bilayers of the zwitterionic phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), which was selectively deuterated at the headgroup in the choline alpha- and beta-methylene segments and the choline gamma-methyl groups. Complexes of DMPC/BR contents from 67:1 to 222:1 (mol/mol) were produced under conditions to promote formation of large vesicles (mean diameters 600-700 nm). The magnitudes of the 2H-NMR quadrupole splittings recorded from the deuterium-labelled headgroup segments, and the 31P-NMR chemical shift anisotropy (CSA) of the phosphate group appeared to vary linearly with the BR content in the complexes over the range of DMPC/BR ratios studied. On increasing the proportion of BR in the DMPC-BR complexes, the 2H-NMR quadrupole splittings measured from the choline gamma-methyl groups and the beta-methylene segments and the 31P-NMR CSA increased in magnitude, while the 2H-NMR quadrupole splitting from the alpha-methylene segment decreased. Such opposing changes in the choline alpha- and beta-methylene segment quadrupole splittings are similar to those reported on increasing the proportion of positively charged amphiphile at the bilayer surface (Seelig et al. (1987) Biochemistry 26, 7535-7541). It is suggested that BR presents a net positive charge to the phosphocholine headgroups at the protein/lipid interface.
authors.affiliation: Department of Biochemistry, University of Oxford, UK.
authors.forename: P
authors.initials: P
authors.lastname: Gale
authors.forename: A
authors.initials: A
authors.lastname: Watts
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D019617:Halobacterium salinarum / Q000378:metabolism; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008968:Molecular Conformation; D010758:Phosphorus; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D010758:Phosphorus; D001436:Bacteriorhodopsins; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine