Structural and functional aspects of the multidrug efflux pump AcrB

Eicher, Thomas; Brandstätter, Lorenz; Pos, Klaas M.

doi:10.1515/bc.2009.090

Cited by 53 publications

(47 citation statements)

References 75 publications

(97 reference statements)

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“…These genes are part of the acid resistance systems (18). Expression of a pH-inducible protein involved in the stress response (inaA), the major oxygen-insensitive nitroreductase (nfsAB), and the multidrug efflux transporters (acrAB and mdtG) (19) was significantly induced in tetracyclineand enrofloxacin-resistant cells. The regulator of acrAB, acrR, was upregulated 5.9 times in enrofloxacin-resistant cells, resulting in a very comparable upregulation of acrA by a factor of 7.9 and acrB by a factor of 5.8.…”

Section: Resultsmentioning

confidence: 99%

Interaction between Mutations and Regulation of Gene Expression during Development of De Novo Antibiotic Resistance

Händel

Schuurmans

Feng

et al. 2014

Antimicrob Agents Chemother

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bBacteria can become resistant not only by horizontal gene transfer or other forms of exchange of genetic information but also by de novo by adaptation at the gene expression level and through DNA mutations. The interrelationship between changes in gene expression and DNA mutations during acquisition of resistance is not well documented. In addition, it is not known whether the DNA mutations leading to resistance always occur in the same order and whether the final result is always identical. The expression of >4,000 genes in Escherichia coli was compared upon adaptation to amoxicillin, tetracycline, and enrofloxacin. During adaptation, known resistance genes were sequenced for mutations that cause resistance. The order of mutations varied within two sets of strains adapted in parallel to amoxicillin and enrofloxacin, respectively, whereas the buildup of resistance was very similar. No specific mutations were related to the rather modest increase in tetracycline resistance. Ribosome-sensed induction and efflux pump activation initially protected the cell through induction of expression and allowed it to survive low levels of antibiotics. Subsequently, mutations were promoted by the stress-induced SOS response that stimulated modulation of genetic instability, and these mutations resulted in resistance to even higher antibiotic concentrations. The initial adaptation at the expression level enabled a subsequent trial and error search for the optimal mutations. The quantitative adjustment of cellular processes at different levels accelerated the acquisition of antibiotic resistance. The de novo acquisition of resistance against antibiotics is known to be accompanied by certain mutations and differential expression of specific genes (1-5). The "radical-based" theory (6, 7) proposes that bactericidal antibiotics cause cell death by a single mechanism, driven by the accumulation of oxygen radicals in the cells. In that case, the cellular response to sublethal concentrations of antibiotics should be similar even for compounds belonging to different classes of bactericidal drugs, such as beta-lactams or fluoroquinolones. The outcome might differ for bacteriostatic drugs, for example, tetracycline. The radical-based theory, however, is the subject of debate (8). The revelation of a common denominator for the adaptation processes to different antibiotics might illuminate the question of a single mechanism from a different angle.Resistance can easily be induced in Escherichia coli by exposure to stepwise increasing sublethal antibiotic concentrations (9). The effects of the acquisition of resistance to amoxicillin on the overall physiology is a complex set of adaptations at the gene expression level, preventing metabolic costs at the expense of the ecological range (10). After the initial stage, the prolonged exposure to antibiotics modulates the SOS response, leading in turn to mutations that cause resistance (11). The mutations generate more permanent resistance, which remains long after the antibiotic pressure has been ...

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Section: Resultsmentioning

confidence: 99%

Interaction between Mutations and Regulation of Gene Expression during Development of De Novo Antibiotic Resistance

Händel

Schuurmans

Feng

et al. 2014

Antimicrob Agents Chemother

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“…The efficiency of restoration depends on the respective affinities of the transported drugs and the tested compound for affinity/ binding sites located inside the efflux pump system. These sites have been proposed from the co-crystallographic analyses (Yu et al, 2003(Yu et al, , 2005 and modelling studies carried out on the AcrB pump (Eicher et al, 2009;Li & Nikaido, 2009;Murakami, 2008;Nikaido & Takatsuka, 2009;Pos, 2009;Takatsuka et al, 2010). Consequently, as the concentration of the compound is increased, competition for these internal binding sites (Nagano & Nikaido, 2009) favours the compound, depending on the respective affinity constant ratio, thereby promoting the intrabacterial retention of the antibiotic.…”

Section: Discussionmentioning

confidence: 99%

An alkylaminoquinazoline restores antibiotic activity in Gram-negative resistant isolates

et al. 2011

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To date, various bacterial drug efflux pump inhibitors (EPIs) have been described. They exhibit variability in their activity spectrum with respect to antibiotic structural class and bacterial species. Among the various 4-alkylaminoquinazoline derivatives synthesized and studied in this work, one molecule, 1167, increased the susceptibility of important human-pathogenic, resistant, Gram-negative bacteria towards different antibiotic classes. This 4-(3-morpholinopropylamino)-quinazoline induced an increase in the activity of chloramphenicol, nalidixic acid, norfloxacin and sparfloxacin, which are substrates of the AcrAB-TolC and MexAB-OprM efflux pumps that act in these multidrug-resistant isolates. In addition, 1167 increased the intracellular concentration of chloramphenicol in efflux pump-overproducing strains. The rate of restoration depended on the structure of the antibiotic, suggesting that different sites in the efflux pumps may be involved. A molecule exhibiting a morpholine functional group and a propyl extension of the side chain was more active.

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“…Data predominantly from crystallization and computer modeling studies have suggested a vestibule and a cleft entrance. The vestibule channel appears to be opened to the so-called "groove" between TM8 and TM9 and is thought to trap substrates from the outer leaflet of the inner membrane, whereas the cleft pathway is thought to allow the entrance of substrates from the periplasm between subdomains PC1 and PC2 further apart from the upper ending of the TM domain (9,(12)(13)(14)(20)(21)(22). A third option, an entrance on the back side of AcrB open to the central cavity built from the intermolecular space between the protomers is considered to be less likely (13,21).…”

mentioning

confidence: 99%

Evidence of a Substrate-Discriminating Entrance Channel in the Lower Porter Domain of the Multidrug Resistance Efflux Pump AcrB

Schuster

Vavra

Kern

2016

Antimicrob Agents Chemother

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Efflux pumps of the resistance nodulation cell division (RND) transporter family, such as AcrB of Escherichia coli, play an important role in the development of multidrug resistance, but the molecular basis for their substrate promiscuity is not yet completely understood. From a collection of highly clarithromycin-resistant AcrB periplasmic domain mutants derived from in vitro random mutagenesis, we identified variants with an unusually altered drug resistance pattern characterized by increased susceptibility to many drugs of lower molecular weight, including fluoroquinolones, tetracyclines, and oxazolidinones, but unchanged or increased resistance to drugs of higher molecular weight, including macrolides. Sequencing of 14 such "divergent resistance" phenotype mutants and 15 control mutants showed that this unusual phenotype was associated with mutations at residues I38 and I671 predominantly to phenylalanine and threonine, respectively, both conferring a similar susceptibility pattern. Reconstructed I38F and I671T single mutants as well as an engineered I38F I671T double mutant with proved efflux competence revealed an equivalent phenotype with enhanced or unchanged resistance to many large AcrB substrates but increased susceptibility to several lower-molecular-weight drugs known to bind within the distal binding pocket. The two isoleucines located in close vicinity to each other in the lower porter domain of AcrB beneath the bottom of the proximal binding pocket may be part of a preferential small-drug entrance pathway that is compromised by the mutations. This finding supports recent indications of distinct entrance channels used by compounds with different physicochemical properties, of which molecular size appears to play a prominent role. Bacterial multidrug resistance (MDR) is one of the great challenges in view of increasing resistance rates, particularly among Gram-negative pathogens and limited development of new therapeutic compounds (1). In Gram-negative bacteria, the outer membrane influx barrier and MDR efflux contribute to poor susceptibility to various antibiotics (2, 3). Several classes of bacterial drug exporters are known (4, 5), among them the resistance nodulation cell division (RND)-type transporters, which are considered the most efficient MDR efflux systems of Gram-negative organisms. RND pumps cooperate with an outer membrane channel and membrane fusion proteins, thereby bridging the inner membrane, the periplasm, and the outer membrane. Some of the RND pumps have a narrow substrate range (e.g., the aminoglycoside exporter AcrD from Escherichia coli and MexY from Pseudomonas aeruginosa), while many of them confer resistance to a wide variety of chemically unrelated compounds. The latter group includes the constitutively expressed trimeric exporter AcrB, the major MDR efflux pump of E. coli which works together with the outer membrane channel TolC and the AcrA membrane fusion proteins.AcrB serves as a model RND transporter and has been extensively investigated. Anchored in the inner membr...

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Structural and functional aspects of the multidrug efflux pump AcrB

Cited by 53 publications

References 75 publications

Interaction between Mutations and Regulation of Gene Expression during Development of De Novo Antibiotic Resistance

Interaction between Mutations and Regulation of Gene Expression during Development of De Novo Antibiotic Resistance

An alkylaminoquinazoline restores antibiotic activity in Gram-negative resistant isolates

Evidence of a Substrate-Discriminating Entrance Channel in the Lower Porter Domain of the Multidrug Resistance Efflux Pump AcrB

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