title: Pseudomonas aeruginosa porin OprF: properties of the channel.
abstract: Using ion channel reconstitution in planar lipid bilayers, we examined the channel-forming activity of subfractions of Pseudomonas aeruginosa OprF, which was shown to exist in two different conformations: a minority single domain conformer and a majority two-domain conformer (Sugawara, E., Nestorovich, E. M., Bezrukov, S. M., and Nikaido, H. (2006) J. Biol. Chem. 281, 16220-16229). With the fraction depleted for the single domain conformer, we were unable to detect formation of any channels with well defined conductance levels. With the unfractionated OprF, we saw only rare channel formation. However, with the single domain-enriched fraction of OprF, we observed regular insertion of channels with highly reproducible conductances. Single OprF channels demonstrate rich kinetic behavior exhibiting spontaneous transitions between several subconformations that differ in ionic conductance and radius measured in polymer exclusion experiments. Although we showed that the effective radius of the most conductive conformation exceeds that of the general outer membrane porin of Escherichia coli, OmpF, we also found that a single OprF channel mainly exists in weakly conductive subconformations and switches to the fully open state for a short time only. Therefore, the low permeability of OprF reported earlier may be due to two factors: mainly to the paucity of the single domain conformer in the OprF population and secondly to the predominance of weakly conductive subconformations within the single domain conformer.
authors.affiliation: Laboratory of Physical and Structural Biology, NICHD/National Institutes of Health, 9 Memorial Drive, Bethesda, MD 20892-0924, USA.
authors.forename: Ekaterina M
authors.initials: EM
authors.lastname: Nestorovich
authors.forename: Etsuko
authors.initials: E
authors.lastname: Sugawara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nikaido
authors.forename: Sergey M
authors.initials: SM
authors.lastname: Bezrukov
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry; D007477:Ions; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry; D018272:Porins / Q000737:chemistry / Q000502:physiology*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D050994:Voltage-Dependent Anion Channels / Q000737:chemistry
chemical_list: D001425:Bacterial Outer Membrane Proteins; D007477:Ions; D008051:Lipid Bilayers; D008081:Liposomes; D011108:Polymers; D018272:Porins; D050994:Voltage-Dependent Anion Channels