Effect of lipid bilayer properties on the photocycle of green proteorhodopsin.
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.
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Ljubica
L
Lindholm
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Candan
C
Ariöz
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Michael
M
Jawurek
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Jobst
J
Liebau
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Lena
L
Mäler
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Åke
Å
Wieslander
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden. Electronic address: christoph.vonballmoos@dcb.unibe.se.
Christoph
C
von Ballmoos
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden. Electronic address: barth@dbb.su.se.
Andreas
A
Barth
D003902:Detergents / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D008563:Membrane Lipids / Q000737:chemistry* / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D010782:Photolysis; D017440:Photoperiod; D025604:Rhodopsins, Microbial / Q000378:metabolism* / Q000528:radiation effects
D003902:Detergents; D008051:Lipid Bilayers; D008081:Liposomes; D008563:Membrane Lipids; D010743:Phospholipids; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin
Bicelle; Detergent; Lipid; Membrane protein; Photocycle; Proteorhodopsin