title: Electrostatic effects influence the formation of two-dimensional crystals of bacteriorhodopsin reconstituted into dimyristoylphosphatidylcholine membranes.
abstract: We examined how electrostatic shielding affects the formation of two-dimensional (2D) crystals of bacteriorhodopsin (bR) in reconstituted dimyristoylphosphatidylcholine (DMPC) membranes by varying the sodium chloride (NaCl) concentration. The 2D crystalline array of bR formed in the gel phase of DMPC membranes was characterized by a symmetric bipolar pattern in visible circular dichroic spectra collected around 560 nm. The amplitude of the bipolar pattern was systematically enhanced by increasing the NaCl concentration. A strong correlation between the amplitude of the bipolar pattern and the Debye constant of small ions indicated that a weakening of electrostatic repulsion by the shielding effect of small ions enhances the order of 2D bR crystals in the gel phase of DMPC membranes. Considering the 3D distribution of charged residues, we propose a model of interaction balance in reconstituted bR membranes in which effective attraction between bR molecules occurs as a result of the phase separation of the DMPC membrane in the gel phase overcoming electrostatic repulsion between bR molecules.
authors.affiliation: Department of Applied Physics, Graduate School of Engineering, Nagoya University, Japan. lnegishi@bio.titech.ac.jp
authors.forename: Lumi
authors.initials: L
authors.lastname: Negishi
authors.forename: Shigeki
authors.initials: S
authors.lastname: Mitaku
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D002942:Circular Dichroism; D003460:Crystallization; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D019617:Halobacterium salinarum; D007477:Ions / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D044367:Phase Transition; D012965:Sodium Chloride / Q000737:chemistry; D055672:Static Electricity
chemical_list: D007477:Ions; D008051:Lipid Bilayers; D012965:Sodium Chloride; D001436:Bacteriorhodopsins; D004134:Dimyristoylphosphatidylcholine