title: Structure of the monomeric outer-membrane porin OmpG in the open and closed conformation.
abstract: OmpG, a monomeric pore-forming protein from Escherichia coli outer membranes, was refolded from inclusion bodies and crystallized in two different conformations. The OmpG channel is a 14-stranded beta-barrel, with short periplasmic turns and seven extracellular loops. Crystals grown at neutral pH show the channel in the open state at 2.3 A resolution. In the 2.7 A structure of crystals grown at pH 5.6, the pore is blocked by loop 6, which folds across the channel. The rearrangement of loop 6 appears to be triggered by a pair of histidine residues, which repel one another at acidic pH, resulting in the breakage of neighbouring H-bonds and a lengthening of loop 6 from 10 to 17 residues. A total of 151 ordered LDAO detergent molecules were found in the 2.3 A structure, mostly on the hydrophobic outer surface of OmpG, mimicking the outer membrane lipid bilayer, with three LDAO molecules in the open pore. In the 2.7 A structure, OmpG binds one OG and one glucose molecule as sugar substrates in the closed pore.
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: Ozkan
authors.initials: O
authors.lastname: Yildiz
authors.forename: Kutti R
authors.initials: KR
authors.lastname: Vinothkumar
authors.forename: Panchali
authors.initials: P
authors.lastname: Goswami
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry*; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry; D008969:Molecular Sequence Data; D018272:Porins / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; C114347:OmpG protein, E coli; D018272:Porins; D005947:Glucose