Colistin-Resistant, Lipopolysaccharide-Deficient Acinetobacter baumannii Responds to Lipopolysaccharide Loss through Increased Expression of Genes Involved in the Synthesis and Transport of Lipoproteins, Phospholipids, and Poly-β-1,6-
            <i>N</i>
            -Acetylglucosamine

Henry, Rebekah; Vithanage, Nuwam R; Harrison, Paul F.; Seemann, Torsten; Coutts, Scott; Moffatt, Jennifer H.; Nation, Roger L.; Li, Jian; Harper, Marina; Adler, Ben; Boyce, John D.

doi:10.1128/aac.05191-11

Cited by 165 publications

(179 citation statements)

References 56 publications

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“…Despite the fact that the Lol system is widely conserved across the gammaproteobacteria, activity was seen in only E. coli and H. influenzae. At present, it is not clear why cellular activity was not seen against a wider range of gammaproteobacteria, as the five Lol proteins are highly conserved across species (37), with the exception of Acinetobacter baumannii, for which no clear homolog of LolC has been identified (44). Some other clinically relevant gammaproteobacteria, such as P. aeruginosa, are notorious for their resistance to antibiotics due to the impermeability of their outer membranes and active efflux systems.…”

Section: Discussionmentioning

confidence: 97%

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

et al. 2015

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cIn Gram-negative bacteria, lipoproteins are transported to the outer membrane by the Lol system. In this process, lipoproteins are released from the inner membrane by the ABC transporter LolCDE and passed to LolA, a diffusible periplasmic molecular chaperone. Lipoproteins are then transferred to the outer membrane receptor protein, LolB, for insertion in the outer membrane. Here we describe the discovery and characterization of novel pyridineimidazole compounds that inhibit this process. Escherichia coli mutants resistant to the pyridineimidazoles show no cross-resistance to other classes of antibiotics and map to either the LolC or LolE protein of the LolCDE transporter complex. The pyridineimidazoles were shown to inhibit the LolA-dependent release of the lipoprotein Lpp from E. coli spheroplasts. These results combined with bacterial cytological profiling are consistent with LolCDE-mediated disruption of lipoprotein targeting to the outer membrane as the mode of action of these pyridineimidazoles. The pyridineimidazoles are the first reported inhibitors of the LolCDE complex, a target which has never been exploited for therapeutic intervention. These compounds open the door to further interrogation of the outer membrane lipoprotein transport pathway as a target for antimicrobial therapy.T he most distinguishing feature of Gram-negative bacteria is their cell envelope, which is comprised of both an inner and an outer membrane bilayer. The outer membrane has a unique composition of lipoproteins, ␤-barrel proteins, lipopolysaccharides, and phospholipids. Lipoproteins, membrane proteins that are covalently modified with lipids, are involved in a variety of integral cellular functions, such as the synthesis and maintenance of the cell surface and the transport of substrates (reviewed in reference 1). Lipoproteins are synthesized as precursors in the cytoplasm. Upon transit across the inner membrane by either the Sec or Tat machinery, the export signal peptide is cleaved, and attached to its amino terminus is a lipid moiety. This lipid serves as a membrane anchor for the lipoprotein. Some lipoproteins remain in the outer leaflet of the inner membrane, while others must cross the hydrophilic periplasmic space to the outer membrane. This sorting of lipoproteins to the outer membrane is achieved by the Lol system, which consists of five proteins (Fig. 1) (reviewed in reference 1). In this process, lipoproteins destined for the outer membrane are released from the inner membrane by the LolCDE complex, an inner membrane ABC transporter. LolCDE transfers the lipoproteins to LolA, a diffusible periplasmic chaperone (2, 3). LolA then transfers the lipoprotein to LolB, the outer membrane lipoprotein receptor, which incorporates these lipoproteins into the inner leaflet of the outer membrane (1, 4). This is in contrast to Grampositive bacteria, which have a single membrane bilayer; therefore, localization of lipoproteins to the cell surface requires only export through the cytoplasmic membrane and acylation (5).Infections c...

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Section: Discussionmentioning

confidence: 97%

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

et al. 2015

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“…However, little is known about the regulation of Lol protein expression, although lipopolysaccharide-deficient Acinetobacter baumannii was very recently reported to exhibit increased expression levels of genes involved in lipoprotein trans- port, such as LolA, LolB, LolE, and LolD, to various extents (18). No clear homolog of LolC was identified in this gammaproteobacterium.…”

Section: Discussionmentioning

confidence: 99%

Defective Lipoprotein Sorting Induces lolA Expression through the Rcs Stress Response Phosphorelay System

2012

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cThe Escherichia coli LolA protein is a lipoprotein-specific chaperone that carries lipoproteins from the inner to the outer membrane. A dominant negative LolA mutant, LolA(I93C/F140C), in which both 93 Ile and 140 Phe are replaced by Cys, binds tightly to the lipoprotein-dedicated ABC transporter LolCDE complex on the inner membrane and therefore inhibits the detachment of outer membrane-specific lipoproteins from the inner membrane. We found that the expression of this mutant strongly induced lolA gene transcription. The depletion of the LolA or LolB protein also triggered lolA gene transcription, indicating that the inhibition of outer membrane lipoprotein transport triggers lolA transcription. To elucidate the mechanism, we isolated mutants that are unable to induce lolA transcription using the lacZ gene fused to the lolA promoter as a reporter and found that the Rcs phosphorelay system directly regulates lolA transcription. An outer membrane lipoprotein, RcsF, was essential for this activation, while the coactivator RcsA was dispensable. Taking the observation that an RcsF mutant localized in the inner membrane constitutively activated the Rcs phosphorelay system into consideration, the results shown here strongly suggest that correct lipoprotein sorting to the outer membrane is monitored by RcsF, which plays a key role in the Rcs stress response system.

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“…encode the genes for a T6SS, including Acinetobacter noscomialis and Acinetobacter baylyi, which possess a constitutively active antibacterial T6SS (20)(21)(22)(23)(24). A. baumannii strains have been shown by us and others to secrete Hcp (21,25), but to our knowledge a T6SS-dependent phenotype has not been ascribed to this species. Furthermore, our previous results showed that Hcp secretion is highly variable between A. baumannii strains, with some isolates carrying an inactive system (21).…”

mentioning

confidence: 99%

A multidrug resistance plasmid contains the molecular switch for type VI secretion in Acinetobacter baumannii

Weber

Irwin

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

161

190

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Infections with Acinetobacter baumannii, one of the most troublesome and least studied multidrug-resistant superbugs, are increasing at alarming rates. A. baumannii encodes a type VI secretion system (T6SS), an antibacterial apparatus of Gram-negative bacteria used to kill competitors. Expression of the T6SS varies among different strains of A. baumannii, for which the regulatory mechanisms are unknown. Here, we show that several multidrug-resistant strains of A. baumannii harbor a large, self-transmissible resistance plasmid that carries the negative regulators for T6SS. T6SS activity is silenced in plasmid-containing, antibiotic-resistant cells, while part of the population undergoes frequent plasmid loss and activation of the T6SS. This activation results in T6SS-mediated killing of competing bacteria but renders A. baumannii susceptible to antibiotics. Our data show that a plasmid that has evolved to harbor antibiotic resistance genes plays a role in the differentiation of cells specialized in the elimination of competing bacteria.

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Colistin-Resistant, Lipopolysaccharide-Deficient Acinetobacter baumannii Responds to Lipopolysaccharide Loss through Increased Expression of Genes Involved in the Synthesis and Transport of Lipoproteins, Phospholipids, and Poly-β-1,6- N -Acetylglucosamine

Cited by 165 publications

References 56 publications

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

Small-Molecule Inhibitors of Gram-Negative Lipoprotein Trafficking Discovered by Phenotypic Screening

Defective Lipoprotein Sorting Induces lolA Expression through the Rcs Stress Response Phosphorelay System

A multidrug resistance plasmid contains the molecular switch for type VI secretion in Acinetobacter baumannii

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