Osmoporin <scp>OmpC</scp> forms a complex with <scp>MlaA</scp> to maintain outer membrane lipid asymmetry in <scp><i>E</i></scp><i>scherichia coli</i>

Chong, Zhi-Soon; Woo, Wei-Fen; Chng, Shu‐Sin

doi:10.1111/mmi.13202

Cited by 129 publications

(200 citation statements)

References 52 publications

(89 reference statements)

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“…However, due to its toxicity, the yebT-expressing plasmid did not complement the hypersensitivity (data not shown). It was reported that the Mla pathway depends on OmpC porin for its function (21). However, even in the ΔmlaD ompC background, deletion of both the pqiABC and yebST operons rendered cells sensitive to SDS-EDTA (Fig.…”

Section: Resultsmentioning

confidence: 99%

pqiABC and yebST , Putative mce Operons of Escherichia coli, Encode Transport Pathways and Contribute to Membrane Integrity

Nakayama

Zhang-Akiyama

2017

J Bacteriol

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The membranes of single-cell organisms are crucial as the first line of defense. The outer membrane of Gram-negative bacteria is an asymmetric bilayer in which lipopolysaccharides (LPSs) and phospholipids are localized in the outer and inner leaflet, respectively. This asymmetry is important for membrane integrity. In Escherichia coli, the Mla transport pathway maintains this asymmetry by removing phospholipids from the outer leaflet. The MlaD component of this system is a mammalian cell entry (MCE) domain protein, and E. coli has two other MCE domain proteins of unknown function (PqiB and YebT). Here, we show that these two proteins are components of novel transport pathways that contribute to membrane integrity. The pqiAB operon is regulated by SoxS and RpoS. The yebST operon contains pqiAB homologues. Here, we found a third member of the pqi operon, ymbA (pqiC). A PqiB-PqiC complex bridges the inner and the outer membrane, and in other bacteria, pqiBC genes are located in operons together with transporter proteins. We show here that simultaneous deletion of pqiABC and yebST operons in an Δmla background rendered cells more sensitive to SDS-EDTA, and the SDS-EDTA sensitivity of mla mutants was rescued by additional copies of pqiABC. We also found that the yebST operon was induced by a defect in LPS molecules. In conclusion, PqiABC and YebST are novel transport pathways related to the Mla transport pathway and important for membrane integrity.IMPORTANCE Membranes of bacteria are crucial for stress resistance. The composition of the E. coli outer membrane is asymmetric, with asymmetry maintained by the Mla ABC transport pathway. We propose that the stress-inducible pqiABC operon and homologous yebST operon, both of previously unknown function, encode transport pathway proteins related to the Mla transport pathway. Deletion of these operons rendered cells more sensitive to membrane stress, and additional copies of pqiABC suppressed the SDS-EDTA sensitivity of mla mutant strains. We found that yebS=-=lacZ fusion was activated in mutant strains with defective LPS molecules.KEYWORDS SoxS, membranes, oxidative stress, pqiABC, yebST E scherichia coli, a Gram-negative bacterium, has an inner membrane (IM) and an outer membrane (OM). Since these membranes separate essential cellular components from the environment, they are important for stress resistance (1, 2). The OM of E. coli is an asymmetric bilayer in which lipopolysaccharides (LPSs) and phospholipids (PLs) are localized in the outer and the inner leaflet, respectively (3). Lipophilic molecules easily penetrate a bilayer of PLs. Because of the low fluidity of lipid A (the lipid portion of LPSs), the asymmetric OM performs a barrier function against lipophilic molecules (3). Mutant strains with defective LPSs are also sensitive to hydrophilic molecules, presumably due to transient cracks in the OM (3). Therefore, disruption of

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Section: Resultsmentioning

confidence: 99%

pqiABC and yebST , Putative mce Operons of Escherichia coli, Encode Transport Pathways and Contribute to Membrane Integrity

Nakayama

Zhang-Akiyama

2017

J Bacteriol

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“…Some ABC transports are involved in the biogenesis of the outer membrane and are important for maintaining outer membrane integrity and stability (50,54,55). Disruption of such transporters adversely affects membrane integrity and stability, which in turn affects the cell's susceptibilities to toxic compounds.…”

Section: Resultsmentioning

confidence: 99%

A PhoPQ-Regulated ABC Transporter System Exports Tetracycline in Pseudomonas aeruginosa

Chen

Duan

2016

Antimicrob Agents Chemother

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bPseudomonas aeruginosa is an important human pathogen whose infections are difficult to treat due to its high intrinsic resistance to many antibiotics. Here, we show that the disruption of PA4456, encoding the ATP binding component of a putative ATP-binding cassette (ABC) transporter, increased the bacterium's susceptible to tetracycline and other antibiotics or toxic chemicals. Fluorescence spectroscopy and antibiotic accumulation tests showed that the interruption of the ABC transporter caused increased intracellular accumulation of tetracycline, demonstrating a role of the ABC transporter in tetracycline expulsion. Site-directed mutagenesis proved that the conserved residues of E170 in the Walker B motif and H203 in the H-loop, which are important for ATP hydrolysis, were essential for the function of PA4456. Through a genome-wide search, the PhoPQ twocomponent system was identified as a regulator of the computationally predicted PA4456-4452 operon that encodes the ABC transporter system. A >5-fold increase of the expression of this operon was observed in the phoQ mutant. The results obtained also show that the expression of the phzA1B1C1D1E1 operon and the production of pyocyanin were significantly higher in the ABC transporter mutant, signifying a connection between the ABC transporter and pyocyanin production. These results indicated that the PhoPQ-regulated ABC transporter is associated with intrinsic resistance to antibiotics and other adverse compounds in P. aeruginosa, probably by extruding them out of the cell.

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“…Indeed, in contrast to PldA, which requires calcium for activity, PagP levels are increased by the PhoPQ stress response under conditions of divalent cation limitation [55,58]. In addition to fortifying the OM barrier, palmitoylated lipid A can also alter the innate immune response and has proven a useful experimental tool as a probe to monitor ectopic exposure of PLs in the OM [50,59,60]. Although the fate of the lyso-PL by-products of PagP activity is unclear, systems exist to recycle these lipids [61,62], which will be discussed further in Section 4.1…”

Section: – Maintenance Of Om Asymmetrymentioning

confidence: 99%

“…How phospholipids could be flipped to the inner leaflet of the OM, which is devoid of an obvious energy source, is not yet clear. The OM lipoprotein component MlaA has been shown to interact with the OM protein porin OmpC, and deletion of this porin has a similar phenotype to mlaA null mutants under some, but not all, conditions [59]. These observations led to the proposal that the porin may facilitate transbilayer movement of mislocalized PLs [59].…”

Section: – Maintenance Of Om Asymmetrymentioning

confidence: 99%

Making a membrane on the other side of the wall

May

Silhavy

2017

Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biolog

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The outer membrane (OM) of Gram-negative bacteria is positioned at the frontline of the cell’s interaction with its environment and provides a barrier against influx of external toxins while still allowing import of nutrients and excretion of wastes. It is a remarkable asymmetric bilayer with a glycolipid surface-exposed leaflet and a glycerophospholipid inner leaflet. Lipid asymmetry is key to OM barrier function and several different systems actively maintain this lipid asymmetry. All OM components are synthesized in the cytosol before being secreted and assembled into a contiguous membrane on the other side of the cell wall. Work in recent years has uncovered the pathways that transport and assemble most of the OM components. However, our understanding of how phospholipids are delivered to the OM remains notably limited. Here we will review seminal works in phospholipid transfer performed some 40 years ago and place more recent insights in their context.

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Osmoporin OmpC forms a complex with MlaA to maintain outer membrane lipid asymmetry in Escherichia coli

Cited by 129 publications

References 52 publications

pqiABC and yebST , Putative mce Operons of Escherichia coli, Encode Transport Pathways and Contribute to Membrane Integrity

pqiABC and yebST , Putative mce Operons of Escherichia coli, Encode Transport Pathways and Contribute to Membrane Integrity

A PhoPQ-Regulated ABC Transporter System Exports Tetracycline in Pseudomonas aeruginosa

Making a membrane on the other side of the wall

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