title: High salt concentrations increase permeability through OmpC channels of Escherichia coli.
abstract: OmpF and OmpC porin channels are responsible for the passage of small hydrophilic solutes across the outer membrane of Escherichia coli. Although these channels are two of the most extensively studied porin channels, what had yet remained elusive was the reason why OmpC shows markedly lower permeability than OmpF, despite having little difference in its channel size. The OmpC channel, however, is known to contain a larger number of ionizable residues than the OmpF channel. In this study, we examined the channel property of OmpF and OmpC using the intact cell of E. coli, and we found that the permeability of several β-lactams and lactose through OmpC became increased to the level comparable with OmpF with up to 0.3 m salt that may increase the Debye-Hückel shielding or with 2% ethanol or 0.3 m urea that may perturb the short range ordering of water molecules. Replacing 10 pore-lining residues that show different ionization behavior between OmpC and OmpF led to substantial conversion of channel property with respect to their permeability and response to external salt concentration. We thus propose that the overall configuration of ionizable residues in the channel that may orient water molecules and the electrostatic profile of the channel play a decisive role in defining the channel property of the OmpC porin rather than its channel size.
authors.affiliation: Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kojima
authors.affiliation: Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720. Electronic address: nhiroshi@berkeley.edu.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nikaido
mesh_terms: D000645:Ammonium Sulfate / Q000494:pharmacology; D000667:Ampicillin / Q000378:metabolism / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D002463:Cell Membrane Permeability; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism; D015636:Magnesium Chloride / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D020125:Mutation, Missense; D009994:Osmolar Concentration; D010406:Penicillins / Q000378:metabolism / Q000494:pharmacology; D018272:Porins / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; C113724:OmpC protein; D010406:Penicillins; D018272:Porins; D015636:Magnesium Chloride; D012965:Sodium Chloride; D011189:Potassium Chloride; D000667:Ampicillin; D007785:Lactose; D000645:Ammonium Sulfate
keywords: Antibiotics; Gram-negative Bacteria; Outer Membrane; Permeability; Transport
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