3D structure of AcrB: the archetypal multidrug efflux transporter of Escherichia coli likely captures substrates from periplasm

Elkins, Christopher A.; Nikaido, Hiroshi

doi:10.1016/s1368-7646(03)00004-9

Cited by 43 publications

(38 citation statements)

References 17 publications

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“…This point of view is consistent with the recent determination of the three-dimensional structure of AcrB, which is organized as a trimer, in which the three-dimensional structure revealed the presence of vestibules that permit direct access of the substrates from the periplasm or the outer leaflet of the cytoplasmic membrane to its central cavity, with the large periplasmic domains of AcrB being involved in substrate recognition (16,17,20,32,36,44,46,47). Then, the TolC channel, also organized as a trimer (26), would be recruited to form with AcrB a direct transit structure to the extracellular medium (2,16,25,36,37).…”

Section: Discussionsupporting

confidence: 90%

AcrAB-TolC Directs Efflux-Mediated Multidrug Resistance in Salmonella enterica Serovar Typhimurium DT104

Baucheron

Tyler

Boyd

et al. 2004

Antimicrob Agents Chemother

154

125

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Multidrug-resistant Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) strains harbor a genomic island, called Salmonella genomic island 1 (SGI1), which contains an antibiotic resistance gene cluster conferring resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides, and tetracyclines. They may be additionally resistant to quinolones. Among the antibiotic resistance genes there are two, i.e., floR and tet(G), which code for efflux pumps of the major facilitator superfamily with 12 transmembrane segments that confer resistance to chloramphenicol-florfenicol and the tetracyclines, respectively. In the present study we determined, by constructing acrB and tolC mutants, the role of the AcrAB-TolC multidrug efflux system in the multidrug resistance of several DT104 strains displaying additional quinolone resistance or not displaying quinolone resistance. This study shows that the quinolone resistance and the decreased fluoroquinolone susceptibilities of the strains are highly dependent on the AcrAB-TolC efflux system and that single mutations in the quinolone resistance-determining region of gyrA are of little relevance in mediating this resistance. Overproduction of the AcrAB efflux pump, as determined by Western blotting with an anti-AcrA polyclonal antibody, appeared to be the major mechanism of resistance to quinolones. Moreover, chloramphenicol-florfenicol and tetracycline resistance also appeared to be highly dependent on the presence of AcrAB-TolC, since the introduction of mutations in the respective acrB and tolC genes resulted in a susceptible or intermediate resistance phenotype, according to clinical MIC breakpoints, despite the presence of the FloR and Tet(G) efflux pumps. Resistance to other antibiotics, ampicillin, streptomycin, and sulfonamides, was not affected in the acrB and tolC mutants of DT104 strains harboring SGI1. Therefore, AcrAB-TolC appears to direct efflux-mediated resistance to quinolones, chloramphenicol-florfenicol, and tetracyclines in multidrugresistant S. enterica serovar Typhimurium DT104 strains.

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Section: Discussionsupporting

confidence: 90%

AcrAB-TolC Directs Efflux-Mediated Multidrug Resistance in Salmonella enterica Serovar Typhimurium DT104

Baucheron

Tyler

Boyd

et al. 2004

Antimicrob Agents Chemother

154

125

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“…However, as stated above, this change does not appreciably affect its ability to function with VceAB. Models for the assembly of MDR efflux pumps have suggested that the functional docking of an OEP with its corresponding pump involves a two-step process: (i) the physical docking of the OEP with its corresponding CMT-MFP pump and (ii) the opening of the OEP channel (9,12,18,19,27). Our results and those of Andersen et al (4) support that view and suggest that these two steps can be genetically separated.…”

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confidence: 84%

Isolation and Characterization of VceC Gain-of-Function Mutants That Can Function with the AcrAB Multiple-Drug-Resistant Efflux Pump of Escherichia coli

2006

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VceC is the outer membrane component of the major facilitator (MF) VceAB-VceC multiple-drug-resistant (MDR) efflux pump of Vibrio cholerae. TolC is the outer membrane component of the resistance-nodulationdivision AcrAB-TolC efflux pump of Escherichia coli. Although these proteins share little amino acid sequence identity, their crystal structures can be readily superimposed upon one another. In this study, we have asked if TolC and VceC are interchangeable for the functioning of the AcrAB and VceAB pumps. We have found that TolC can replace VceC to form a functional VceAB-TolC MDR pump, but VceC cannot replace TolC to form a functional AcrAB-VceC pump. However, we have been able to isolate gain-of-function (gof) VceC mutants which can functionally interface with AcrAB. These mutations map to four different amino acids located at the periplasmic tip of VceC. Chemical cross-linkage experiments indicate that both wild-type and gof mutant VceC can physically interact with the AcrAB complex, suggesting that these gof mutations are not affecting the recruitment of VceC to the AcrAB complex but rather its ability to functionally interface with the AcrAB pump.

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“…Detailed analysis of the BepE and BepG peptide sequences suggests that both proteins are complete and functional RND transporters. Comparison of these proteins with the AcrB (36) and MexB (31) proteins showed high conservation of key residues involved in protein structure (19,39,70) and proton relay transfer (24) that sustain a possible role of BepE and BepG in multidrug efflux. A similar conclusion was drawn for the BepD and BepF MFP components.…”

Section: Discussionmentioning

confidence: 99%

Interplay between Two RND Systems Mediating Antimicrobial Resistance inBrucella suis

Martín

Posadas

Carrica³

et al. 2009

J Bacteriol

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The RND-type efflux pumps are responsible for the multidrug resistance phenotype observed in many clinically relevant species. Also, RND pumps have been implicated in physiological processes, with roles in the virulence mechanisms of several pathogenic bacteria. We have previously shown that the BepC outer membrane factor of Brucella suis is involved in the efflux of diverse drugs, probably as part of a tripartite complex with an inner membrane translocase. In the present work, we characterize two membrane fusion protein-RND translocases of B. suis encoded by the bepDE and bepFG loci. MIC assays showed that the B. suis ⌬bepE mutant was more sensitive to deoxycholate (DOC), ethidium bromide, and crystal violet. Furthermore, multicopy bepDE increased resistance to DOC and crystal violet and also to other drugs, including ampicillin, norfloxacin, ciprofloxacin, tetracycline, and doxycycline. In contrast to the ⌬bepE mutant, the resistance profile of B. suis remained unaltered when the other RND gene (bepG) was deleted. However, the ⌬bepE ⌬bepG double mutant showed a more severe phenotype than the ⌬bepE mutant, indicating that BepFG also contributes to drug resistance. An open reading frame (bepR) coding for a putative regulatory protein of the TetR family was found upstream of the bepDE locus. BepR strongly repressed the activity of the bepDE promoter, but DOC released the repression mediated by BepR. A clear induction of the bepFG promoter activity was observed only in the BepDE-defective mutant, indicating a regulatory interplay between the two RND efflux pumps. Although only the BepFG-defective mutant showed a moderate attenuation in model cells, the activities of both bepDE and bepFG promoters were induced in the intracellular environment of HeLa cells. Our results show that B. suis harbors two functional RND efflux pumps that may contribute to virulence.Brucella is a facultative intracellular pathogen taxonomically classified within the Alphaproteobacteria, along with other intracellular pathogens, such as Rickettsia, Bartonella, and several plant symbionts and pathogens (7). Brucella spp. are the etiological agents of brucellosis, a major zoonotic disease distributed worldwide and transmitted from domestic, farm, and wild animals to humans. Brucella enters the host through the nasal, oral, and pharyngeal cavities and from there is transported to the proximal lymph nodes. Early during infection, host innate immunity mechanisms contribute to reduce the initial number of infecting brucellae (26). Once in contact with the organism, Brucella is able to invade professional and nonprofessional phagocytes (10). Within the cells, Brucella is found in a membrane-associated vacuole called a Brucellacontaining vacuole. The Brucella-containing vacuole is able to subvert the normal phagocytic pathway to form a vacuole with endoplasmic reticulum markers suitable for Brucella sp. replication (13,50). This strategy helps the bacteria to escape from the bactericidal mechanisms used by the host (7).Host barriers range from anti...

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3D structure of AcrB: the archetypal multidrug efflux transporter of Escherichia coli likely captures substrates from periplasm

Cited by 43 publications

References 17 publications

AcrAB-TolC Directs Efflux-Mediated Multidrug Resistance in Salmonella enterica Serovar Typhimurium DT104

AcrAB-TolC Directs Efflux-Mediated Multidrug Resistance in Salmonella enterica Serovar Typhimurium DT104

Isolation and Characterization of VceC Gain-of-Function Mutants That Can Function with the AcrAB Multiple-Drug-Resistant Efflux Pump of Escherichia coli

Interplay between Two RND Systems Mediating Antimicrobial Resistance inBrucella suis

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