Incorporation of outer membrane protein OmpG in lipid membranes: protein-lipid interactions and beta-barrel orientation.
OmpG is an intermediate size, monomeric, outer membrane protein from Escherichia coli, with n beta = 14 beta-strands. It has a large pore that is amenable to modification by protein engineering. The stoichiometry ( N b = 20) and selectivity ( K r = 0.7-1.2) of lipid-protein interaction with OmpG incorporated in dimyristoyl phosphatidylcholine bilayer membranes was determined with various 14-position spin-labeled lipids by using EPR spectroscopy. The limited selectivity for different lipid species is consistent with the disposition of charged residues in the protein. The conformation and orientation (beta-strand tilt and beta-barrel order parameters) of OmpG in disaturated phosphatidylcholines of odd and even chain lengths from C(12:0) to C(17:0) was determined from polarized infrared spectroscopy of the amide I and amide II bands. A discontinuity in the protein orientation (deduced from the beta-barrel order parameters) is observed at the point of hydrophobic matching of the protein with lipid chain length. Compared with smaller (OmpA; n beta = 8) and larger (FhuA; n beta = 22) monomeric E. coli outer membrane proteins, the stoichiometry of motionally restricted lipids increases linearly with the number of beta-strands, the tilt (beta approximately 44 degrees ) of the beta-strands is comparable for the three proteins, and the order parameter of the beta-barrel increases regularly with n beta. These systematic features of the integration of monomeric beta-barrel proteins in lipid membranes could be useful for characterizing outer membrane proteins of unknown structure.
Anbazhagan
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V
Max-Planck-Institut für biophysikalische Chemie, Abt. Spektroskopie, 37070 Göttingen, Germany.
Qu
J
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Kleinschmidt
J H
JH
Marsh
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D
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D054709:Lecithins; D008051:Lipid Bilayers; D008081:Liposomes / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D018272:Porins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics
D001425:Bacterial Outer Membrane Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D054709:Lecithins; D008051:Lipid Bilayers; D008081:Liposomes; C114347:OmpG protein, E coli; D018272:Porins