title: An elegant means of self-protection in gram-negative bacteria by recognizing and extruding xenobiotics from the periplasmic space.
abstract: Infection of Pseudomonas aeruginosa in cystic fibrosis patients is a major cause of mortality. This organism shows wide ranging antibiotic resistance that is largely attributable to the expression of xenobiotic efflux pump(s). Here, we show a novel mechanism by which the resistance-nodulation-division-type xenobiotic transporter expels potential hazards and protects the interior of the cells. The xenobiotic transporters MexB and MexY preferentially export beta-lactam and aminoglycoside antibiotics, respectively. When two large extramembrane loops of MexY were replaced by the corresponding loops of MexB, the hybrid protein exhibited beta-lactam selectivity (MexB-type), but failed to recognize aminoglycoside. As the transmembrane segment of MexB was replaced with a corresponding transmembrane segment of MexY, one-by-one for all 12 segments, all the hybrid proteins showed MexB-type antibiotic selectivity. These results clearly demonstrated that the resistance-nodulation-division-type efflux pump in P. aeruginosa selects and transports substrates via the domains that largely protrude over the cytoplasmic membrane. The transmembrane segments were unlikely to have been involved in substrate selectivity. These observations led us to propose a novel mechanism by which the xenobiotic transporters in Gram-negative bacteria select and expel substrates from the periplasmic space before potential hazards penetrate into the cytoplasmic membrane.
authors.affiliation: Department of Molecular Life Science, Tokai University School of Medicine, 143 Shimokasuya, Isehara 259-1193, Japan.
authors.forename: Shima
authors.initials: S
authors.lastname: Eda
authors.forename: Hideaki
authors.initials: H
authors.lastname: Maseda
authors.forename: Taiji
authors.initials: T
authors.lastname: Nakae
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D001692:Biological Transport; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006090:Gram-Negative Bacteria / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009154:Mutation; D019897:Periplasm / Q000382:microbiology*; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D013379:Substrate Specificity; D015262:Xenobiotics / Q000494:pharmacology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D026901:Membrane Transport Proteins; C118597:MexB protein, Pseudomonas aeruginosa; C402791:MexXY protein, Pseudomonas aeruginosa; D015262:Xenobiotics