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Validation of inhibitors of an ABC transporter required to transport lipopolysaccharide to the cell surface in Escherichia coli.

ABSTRACT: The presence of lipopolysaccharide (LPS) in the outer leaflet of the outer membrane (OM) of Gram-negative bacteria creates a permeability barrier that prevents the entry of most currently available antibiotics. The seven lipopolysaccharide transport (Lpt) proteins involved in transporting and assembling this glycolipid are essential for growth and division in Escherichia coli; therefore, inhibiting their functions leads to cell death. LptB, the ATPase that provides energy for LPS transport and assembly, forms a complex with three other inner membrane (IM) components, LptC, F, and G. We demonstrate that inhibitors of pure LptB can also inhibit the full IM complex, LptBFGC, purified in detergent. We also compare inhibition of LptB and the LptBFGC complex with the antibiotic activity of these compounds. Our long-term goal is to develop tools to study inhibitors of LPS biogenesis that could serve as potentiators by disrupting the OM permeability barrier, facilitating entry of clinically used antibiotics not normally used to treat Gram-negative infections, or that can serve as antibiotics themselves.

SUBMITTER: Sherman DJ

PROVIDER: S-EPMC3821166 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Validation of inhibitors of an ABC transporter required to transport lipopolysaccharide to the cell surface in Escherichia coli.

Sherman David J DJ Okuda Suguru S Denny William A WA Kahne Daniel D

Bioorganic & medicinal chemistry 20130418 16

The presence of lipopolysaccharide (LPS) in the outer leaflet of the outer membrane (OM) of Gram-negative bacteria creates a permeability barrier that prevents the entry of most currently available antibiotics. The seven lipopolysaccharide transport (Lpt) proteins involved in transporting and assembling this glycolipid are essential for growth and division in Escherichia coli; therefore, inhibiting their functions leads to cell death. LptB, the ATPase that provides energy for LPS transport and a ...[more]

PMID: 23665139

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Project description:The assembly of lipopolysaccharide (LPS) in the outer leaflet of the outer membrane (OM) requires the transenvelope Lpt (lipopolysaccharide transport) complex, made in Escherichia coli of seven essential proteins located in the inner membrane (IM) (LptBCFG), periplasm (LptA), and OM (LptDE). At the IM, LptBFG constitute an unusual ATP binding cassette (ABC) transporter, composed by the transmembrane LptFG proteins and the cytoplasmic LptB ATPase, which is thought to extract LPS from the IM and to provide the energy for its export across the periplasm to the cell surface. LptC is a small IM bitopic protein that binds to LptBFG and recruits LptA via its N- and C-terminal regions, and its role in LPS export is not completely understood. Here, we show that the expression level of lptB is a critical factor for suppressing lethality of deletions in the C-terminal region of LptC and the functioning of a hybrid Lpt machinery that carries Pa-LptC, the highly divergent LptC orthologue from Pseudomonas aeruginosa We found that LptB overexpression stabilizes C-terminally truncated LptC mutant proteins, thereby allowing the formation of a sufficient amount of stable IM complexes to support growth. Moreover, the LptB level seems also critical for the assembly of IM complexes carrying Pa-LptC which is otherwise defective in interactions with the E. coli LptFG components. Overall, our data suggest that LptB and LptC functionally interact and support a model whereby LptB plays a key role in the assembly of the Lpt machinery.The asymmetric outer membrane (OM) of Gram-negative bacteria contains in its outer leaflet an unusual glycolipid, the lipopolysaccharide (LPS). LPS largely contributes to the peculiar permeability barrier properties of the OM that prevent the entry of many antibiotics, thus making Gram-negative pathogens difficult to treat. In Escherichia coli the LPS transporter (the Lpt machine) is made of seven essential proteins (LptABCDEFG) that form a transenvelope complex. Here, we show that increased expression of the membrane-associated ABC protein LptB can suppress defects of LptC, which participates in the formation of the periplasmic bridge. This reveals functional interactions between these two components and supports a role of LptB in the assembly of the Lpt machine.

Project description:Microgravity has been shown to influence the expression of ABC (ATP-Binding Cassette) transporters in bacteria, fungi and mammals, but also to modify the activity of certain cellular components with structural and functional similarities to ABC transporters. Changes in activity of ABC transporters could lead to important metabolic disorders and undesired pharmacological effects during spaceflights. However, no current means exist to study the functionality of these transporters in microgravity. To this end, a Vesicular Transport Assay (®) (Solvo Biotechnology, Hungary) was adapted to evaluate multi-drug resistance-associated protein 2 (MRP2) trans-membrane estradiol-17-β-glucuronide (E17βG) transport activity, when activated by adenosine-tri-phosphate (ATP) during parabolic flights. Simple diffusion, ATP-independent transport and benzbromarone inhibition were also evaluated. A high accuracy engineering system was designed to perform, monitor and synchronize all procedures. Samples were analysed using a validated high sensitivity drug detection protocol. Experiments were performed in microgravity during parabolic flights, and compared to 1g on ground results using identical equipment and procedures in all cases. Our results revealed that sufficient equipment accuracy and analytical sensitivity were reached to detect transport activity in both gravitational conditions. Additionally, transport activity levels of on ground samples were within commercial transport standards, proving the validity of the methods and equipment used. MRP2 net transport activity was significantly reduced in microgravity, so was signal detected in simple diffusion samples. Ultra-structural changes induced by gravitational stress upon vesicle membranes or transporters could explain the current results, although alternative explanations are possible. Further research is needed to provide a conclusive answer in this regard. Nevertheless, the present validated technology opens new and interesting research lines in biology and human physiology with the potential for significant benefits for both space and terrestrial medicine.

Dataset Information

Validation of inhibitors of an ABC transporter required to transport lipopolysaccharide to the cell surface in Escherichia coli.

Publications

Validation of inhibitors of an ABC transporter required to transport lipopolysaccharide to the cell surface in Escherichia coli.

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