Imp/OstA is required for cell envelope biogenesis in <i>Escherichia coli</i>

Braun, Martin; Silhavy, Thomas J.

doi:10.1046/j.1365-2958.2002.03091.x

Cited by 231 publications

(260 citation statements)

References 36 publications

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“…This higher density might result from an increased protein to lipid ratio. Consistently, whereas OMP assembly appeared unaffected by Imp depletion, both in E. coli (6) and in N. meningitidis (this study), we have demonstrated now that Imp depletion results in decreased levels of LPS in the OM, thus changing the protein:lipid ratio. Also, the observations that missense mutations in the E. coli imp gene resulted in increased sensitivity to hydrophobic agents (7,8) can now be understood: these mutants likely suffered from reduced levels of LPS, a property known to affect the integrity of the OM (23).…”

Section: Discussionsupporting

confidence: 87%

“…The desialylation of a small portion of the LPS observed when whole cells of the imp mutant were treated with neuraminidase was mostly likely due to the diminished membrane integrity in these bacteria, which may have been reinforced by the repeated centrifugation and respuspension steps required for this assay. Because Imp itself is an OMP, as shown by its presence in purified Neisserial (this study) and E. coli (6) OMs, Imp is likely the transporter that mediates the f lip-f lop of LPS over the OM, although an additional role in transport through the periplasm cannot be excluded at this stage.…”

Section: Discussionmentioning

confidence: 80%

“…Braun and Silhavy (6) reported that depletion of Imp in a conditional E. coli mutant resulted in the appearance of highdensity membranes found in sucrose gradient fractionations. This higher density might result from an increased protein to lipid ratio.…”

Section: Discussionmentioning

confidence: 99%

“…Genes involved in the biogenesis of well conserved structures such as LPS are likely highly conserved. This concept appears to be true for the imp gene, because homologs could be found in most Gram-negative, but not in Gram-positive bacteria (6). The absence of an imp homolog in some Gram-negative bacteria appears to correlate with the absence of LPS, because we were unable to find imp homologs in bacteria that possess an OM, but lack LPS biosynthesis genes (1), such as Thermotoga maritima, Deinococcus radiodurans, and the spirochaetes Borrelia burgdorfferi and Treponema pallidum.…”

Section: Phenotype Of a Neisserial Imp Mutantmentioning

confidence: 99%

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Identification of an outer membrane protein required for the transport of lipopolysaccharide to the bacterial cell surface

Bos

Tefsen

Geurtsen

et al. 2004

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

233

226

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Lipopolysaccharide (LPS), also known as endotoxin due to its severe pathophysiological effects in infected subjects, is an essential component of the outer membrane (OM) of most Gramnegative bacteria. LPS is synthesized in the bacterial inner membrane, a process that is now well understood. In contrast, the mechanism of its transport to the outer leaflet of the OM has remained enigmatic. We demonstrate here that the OM protein, known as increased membrane permeability (Imp) or organic solvent tolerance protein, is involved in this process. An Impdeficient mutant of Neisseria meningitidis was viable and produced severely reduced amounts of LPS. The limited amount of LPS that was still produced was not accessible to LPS-modifying enzymes expressed in the OM or added to the extracellular medium. We conclude therefore that Imp mediates the transport of LPS to the cell surface. The role of Imp in LPS biogenesis and its high conservation among Gram-negative bacteria make it an excellent target for the development of novel antibacterial compounds. G ram-negative bacteria are enclosed by a cell envelope consisting of an inner membrane (IM) and an outer membrane (OM), separated by the periplasm. The IM is a phospholipid bilayer, whereas the OM is an asymmetrical bilayer, containing phospholipids in the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. LPS consists of a hydrophobic membrane anchor, lipid A, substituted with a nonrepeating oligosaccharide, the core region. In many bacteria, the core region is extended with the O antigen, a repeating oligosaccharide. The lipid A-core region and the O antigen are synthesized as separate units at the cytoplasmic leaflet of the IM. Almost all of the enzymes involved in their biosynthesis have been identified in Escherichia coli (1, 2). The transport of the lipid A-core moiety to the periplasmic side of the IM is mediated by the MsbA protein, an ATP-binding cassette family transporter (3), whereas flipping of O antigen units over the IM can be facilitated by several distinct mechanisms (1). At the periplasmic side of the IM, the O antigen is ligated to the lipid A-core region. The next step, transport of the fully assembled LPS through the periplasm and across the OM, remains an entirely elusive aspect of LPS biogenesis (1, 2). Recently, Omp85, an essential OMP, was suggested to be involved in this process (4). However, we found a severe OMP assembly defect in a Neisserial Omp85 mutant (5). This phenotype, together with the affinity of Omp85 for OMPs (5) and the presence of omp85 homologs in Gram-negative bacteria lacking LPS, are much more consistent with a role of this protein in OMP assembly, with only an indirect role in LPS transport. Braun and Silhavy (6) identified another essential OMP in E. coli, depletion of which resulted in the formation of aberrant membranes. Missense mutations in the gene encoding this 87-kDa OMP, called increased membrane permeability (Imp) or organic solvent tolerance protein, were already known to affect OM permeability (7,8). He...

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Section: Discussionsupporting

confidence: 87%

Section: Discussionmentioning

confidence: 80%

Section: Discussionmentioning

confidence: 99%

Section: Phenotype Of a Neisserial Imp Mutantmentioning

confidence: 99%

See 2 more Smart Citations

Identification of an outer membrane protein required for the transport of lipopolysaccharide to the bacterial cell surface

Bos

Tefsen

Geurtsen

et al. 2004

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

233

226

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“…Two of these proteins, LptD and LptE (formerly Imp and RlpB, resp. ), reside in the OM and are responsible for the translocation of LPS across the OM (to the cell surface) in the final stages of assembly (8)(9)(10).…”

mentioning

confidence: 99%

The complex that inserts lipopolysaccharide into the bacterial outer membrane forms a two-protein plug-and-barrel

Freinkman

Chng

Kahne

2011

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

159

181

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The cell surfaces of Gram-negative bacteria are composed of lipopolysaccharide (LPS). This glycolipid is found exclusively in the outer leaflet of the asymmetric outer membrane (OM), where it forms a barrier to the entry of toxic hydrophobic molecules into the cell. LPS typically contains six fatty acyl chains and up to several hundred sugar residues. It is biosynthesized in the cytosol and must then be transported across two membranes and an aqueous intermembrane space to the cell surface. These processes are required for the viability of most Gram-negative organisms. The integral membrane β-barrel LptD and the lipoprotein LptE form an essential complex in the OM, which is necessary for LPS assembly. It is not known how this complex translocates large, amphipathic LPS molecules across the OM to the outer leaflet. Here, we show that LptE resides within the LptD β-barrel both in vitro and in vivo. LptD/E associate via an extensive interface; in one specific interaction, LptE contacts a predicted extracellular loop of LptD through the lumen of the β-barrel. Disrupting this interaction site compromises the biogenesis of LptD. This unprecedented two-protein plug-and-barrel architecture suggests how LptD/E can insert LPS from the periplasm directly into the outer leaflet of the OM to establish the asymmetry of the bilayer.lipopolysaccharide assembly | outer membrane protein complex

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