title: Orientation of beta-barrel proteins OmpA and FhuA in lipid membranes. Chain length dependence from infrared dichroism.
abstract: The outer-membrane proteins OmpA and FhuA of Escherichia coli are monomeric beta-barrels of widely differing size. Polarized attenuated total reflection infrared spectroscopy has been used to determine the orientation of the beta-barrels in phosphatidylcholine host matrices of different lipid chain lengths. The linear dichroism of the amide I band from OmpA and FhuA in hydrated membranes generally increases with increasing chain length from diC(12:0) to diC(17:0) phosphatidylcholine, in both the fluid and gel phases. Measurements of the amide I and amide II dichroism from dry samples are used to deduce the strand tilt (beta = 46 degrees for OmpA and beta = 44.5 degrees for FhuA). These values are then used to deduce the order parameters, P(2)(cos alpha), of the beta-barrels from the amide I dichroic ratios of the hydrated membranes. The orientational ordering of the beta-barrels and their assembly in the membrane are discussed in terms of hydrophobic matching with the lipid chains.
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, Abt. Spektroskopie, 37070 Göttingen, Germany.
authors.forename: Muthu
authors.initials: M
authors.lastname: Ramakrishnan
authors.forename: Jian
authors.initials: J
authors.lastname: Qu
authors.forename: Cosmin L
authors.initials: CL
authors.lastname: Pocanschi
authors.forename: Jörg H
authors.initials: JH
authors.lastname: Kleinschmidt
authors.forename: Derek
authors.initials: D
authors.lastname: Marsh
mesh_terms: D000577:Amides; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D008956:Models, Chemical; D010713:Phosphatidylcholines / Q000737:chemistry; D017433:Protein Structure, Secondary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism; D011991:Receptors, Virus / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000577:Amides; D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; C050900:FhuA protein, E coli; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D011956:Receptors, Cell Surface; D011991:Receptors, Virus; C035902:siderophore receptors; C078167:OMPA outer membrane proteins; D007501:Iron