Effect of lipid bilayer properties on the photocycle of green proteorhodopsin

• Published in: Biochimica et biophysica acta 2015-08, Vol.1847 (8), p.698-708
• Main Authors: Lindholm, Ljubica, Ariöz, Candan, Jawurek, Michael, Liebau, Jobst, Mäler, Lena, Wieslander, Åke, von Ballmoos, Christoph, Barth, Andreas
• Format: Article
• Language: English
• Subjects: Bicelle; Detergent; Detergents - chemistry; Detergents - metabolism; Escherichia coli - metabolism; Kinetics; Lipid; Lipid Bilayers - chemistry; Lipid Bilayers - metabolism; Liposomes; Magnetic Resonance Spectroscopy; Membrane Lipids - chemistry; Membrane Lipids - metabolism; Membrane protein; Phospholipids - metabolism; Photocycle; Photolysis; Photoperiod; Proteorhodopsin; Rhodopsins, Microbial - metabolism; Rhodopsins, Microbial - radiation effects
• ISSN: 0005-2728; 0006-3002; 1879-2650; 1879-2650
• DOI: 10.1016/j.bbabio.2015.04.011

The significance of specific lipids for proton pumping by the bacterial rhodopsin proteorhodopsin (pR) was studied. To this end, it was examined whether pR preferentially binds certain lipids and whether molecular properties of the lipid environment affect the photocycle. pR's photocycle was followed by microsecond flash-photolysis in the visible spectral range. It was fastest in phosphatidylcholine liposomes (soy bean lipid), intermediate in 3-[(3-cholamidopropyl) dimethylammonio] propanesulfonate (CHAPS): 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bicelles and in Triton X-100, and slowest when pR was solubilized in CHAPS. In bicelles with different lipid compositions, the nature of the head groups, the unsaturation level and the fatty acid chain length had small effects on the photocycle. The specific affinity of pR for lipids of the expression host Escherichia coli was investigated by an optimized method of lipid isolation from purified membrane protein using two different concentrations of the detergent N-dodecyl-β-d-maltoside (DDM). We found that 11 lipids were copurified per pR molecule at 0.1% DDM, whereas essentially all lipids were stripped off from pR by 1% DDM. The relative amounts of copurified phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin did not correlate with the molar percentages normally present in E. coli cells. The results indicate a predominance of phosphatidylethanolamine species in the lipid annulus around recombinant pR that are less polar than the dominant species in the cell membrane of the expression host E. coli. [Display omitted] •Green proteorhodopsin (pR) is functional in many different lipid environments.•pR's photocycle depends on the lipid system but less on specific phospholipid properties.•Lipids copurified with pR contain mainly phosphatidylethanolamine.•Copurified lipids are less polar than the bulk lipids in the E. coli cell membrane.