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Bacterial outer membrane Edit Wikipedia article
The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the outer membrane of many Gram-negative bacteria includes a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and in some bacteria such as E. coli it is linked to the cell's peptidoglycan by Braun's lipoprotein.
 Clinical significance
If lipid A, part of the LPS, enters the circulatory system it causes a toxic reaction by activating TLR 4. Lipid A is very immunogenic and causes an aggressive response by the immune system. The sufferer will have a high temperature and respiration rate and a low blood pressure. This may lead to endotoxic shock, which may be fatal.
The biogenesis of the outer membrane requires that the individual components are transported from the site of synthesis to their final destination outside the inner membrane by crossing both hydrophilic and hydrophobic compartments. The machinery and the energy source that drive this process are not yet fully understood. The lipid A-core moiety and the O-antigen repeat units are synthesized at the cytoplasmic face of the inner membrane and are separately exported via two independent transport systems, namely, the O-antigen transporter Wzx (RfbX) and the ATP binding cassette (ABC) transporter MsbA that flips the lipid A-core moiety from the inner leaflet to the outer leaflet of the inner membrane. O-antigen repeat units are then polymerised in the periplasm by the Wzy polymerase and ligated to the lipid A-core moiety by the WaaL ligase.
The LPS transport machinery is composed of LptA, LptB, LptC, LptD, LptE. This supported by the fact, that depletion of any of one of these proteins blocks the LPS assembly pathway and results in very similar outer membrane biogenesis defects. Moreover, the location of at least one of these five proteins in every cellular compartment suggests a model for how the LPS assembly pathway is organised and ordered in space.
LptC is equired for the translocation of lipopolysaccharide (LPS) from the inner membrane to the outer membrane. LptE forms a complex with LptD, which is involved in the assembly of LPS in the outer leaflet of the outer membrane and is essential for envelope biogenesis.
 See also
- van der Ley P, Heckels JE, Virji M, Hoogerhout P, Poolman JT (September 1991). "Topology of outer membrane porins in pathogenic Neisseria spp". Infection and immunity 59 (9): 2963–71. PMC 258120. PMID 1652557. http://iai.asm.org/cgi/pmidlookup?view=long&pmid=1652557.
- Feldman MF, Marolda CL, Monteiro MA, Perry MB, Parodi AJ, Valvano MA (December 1999). "The activity of a putative polyisoprenol-linked sugar translocase (Wzx) involved in Escherichia coli O antigen assembly is independent of the chemical structure of the O repeat". J. Biol. Chem. 274 (49): 35129–38. PMID 10574995.
- Liu D, Cole RA, Reeves PR (April 1996). "An O-antigen processing function for Wzx (RfbX): a promising candidate for O-unit flippase". J. Bacteriol. 178 (7): 2102–7. PMC 177911. PMID 8606190. //www.ncbi.nlm.nih.gov/pmc/articles/PMC177911/.
- Doerrler WT, Reedy MC, Raetz CR (April 2001). "An Escherichia coli mutant defective in lipid export". J. Biol. Chem. 276 (15): 11461–4. doi:10.1074/jbc.C100091200. PMID 11278265.
- Polissi A, Georgopoulos C (June 1996). "Mutational analysis and properties of the msbA gene of Escherichia coli, coding for an essential ABC family transporter". Mol. Microbiol. 20 (6): 1221–33. PMID 8809774.
- Zhou Z, White KA, Polissi A, Georgopoulos C, Raetz CR (May 1998). "Function of Escherichia coli MsbA, an essential ABC family transporter, in lipid A and phospholipid biosynthesis". J. Biol. Chem. 273 (20): 12466–75. doi:10.1074/jbc.273.20.12466. PMID 9575204.
- Raetz CR, Whitfield C (2002). "Lipopolysaccharide endotoxins". Annu. Rev. Biochem. 71: 635–700. doi:10.1146/annurev.biochem.71.110601.135414. PMC 2569852. PMID 12045108. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2569852/.
- Sperandeo P, Lau FK, Carpentieri A, De Castro C, Molinaro A, Deho G, Silhavy TJ, Polissi A (July 2008). "Functional analysis of the protein machinery required for transport of lipopolysaccharide to the outer membrane of Escherichia coli". J. Bacteriol. 190 (13): 4460–9. doi:10.1128/JB.00270-08. PMC 2446812. PMID 18424520. //www.ncbi.nlm.nih.gov/pmc/articles/PMC2446812/.
- Wu T, McCandlish AC, Gronenberg LS, Chng SS, Silhavy TJ, Kahne D (August 2006). "Identification of a protein complex that assembles lipopolysaccharide in the outer membrane of Escherichia coli". Proc. Natl. Acad. Sci. U.S.A. 103 (31): 11754–9. doi:10.1073/pnas.0604744103. PMC 1544242. PMID 16861298. //www.ncbi.nlm.nih.gov/pmc/articles/PMC1544242/.
- Bos MP, Tefsen B, Geurtsen J, Tommassen J (June 2004). "Identification of an outer membrane protein required for the transport of lipopolysaccharide to the bacterial cell surface". Proc. Natl. Acad. Sci. U.S.A. 101 (25): 9417–22. doi:10.1073/pnas.0402340101. PMC 438991. PMID 15192148. //www.ncbi.nlm.nih.gov/pmc/articles/PMC438991/.
Lipopolysaccharide-assembly Provide feedback
LptE (formerly known as RplB) is involved in lipopolysaccharide-assembly on the outer membrane of Gram-negative organisms. The lipopolysaccharide component of the outer bacterial membrane is transported from its source of origin to the outer membrane by a set of proteins constituting a transport machinery that is made up of LptA, LptB, LptC, LptD, LptE. LptD appears to be anchored in the outer membrane, and LptE forms a complex with it. This part of the machinery complex is involved in the assembly of lipopolysaccharide in the outer leaflet of the outer membrane .
Sperandeo P, Lau FK, Carpentieri A, De Castro C, Molinaro A, Deho G, Silhavy TJ, Polissi A;, J Bacteriol. 2008;190:4460-4469.: Functional analysis of the protein machinery required for transport of lipopolysaccharide to the outer membrane of Escherichia coli. PUBMED:18424520 EPMC:18424520
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR007485
The cell envelope of Gram-negative bacteria consists of an inner (IM) and an outer membrane (OM) separated by an aqueous compartment, the periplasm, which contains the peptidoglycan layer. The OM is an asymmetric bilayer, with phospholipids in the inner leaflet and lipopolysaccharides (LPS) facing outward [PUBMED:12045108, PUBMED:16357861]. The OM is an effective permeability barrier that protects the cells from toxic compounds, such as antibiotics and detergents, thus allowing bacteria to inhabit several different and often hostile environments. LPS is responsible for the permeability properties of the OM. LPS consists of the lipid A moiety (a glucosamine-based phospholipid) linked to the short core oligosaccharide and the distal O-antigen polysaccharide chain. The core oligosaccharide can be further divided into an inner core, composed of 3-deoxy-D-mannooctulosanate (KDO) and heptose, and an outer core, which has a somewhat variable structure. LPS is essential in most Gram-negative bacteria, with the notable exception of Neisseria meningitidis. The biogenesis of the OM implies that the individual components are transported from the site of synthesis to their final destination outside the IM by crossing both hydrophilic and hydrophobic compartments. The machinery and the energy source that drive this process are not yet fully understood. The lipid A-core moiety and the O-antigen repeat units are synthesized at the cytoplasmic face of the IM and are separately exported via two independent transport systems, namely, the O-antigen transporter Wzx (RfbX) [PUBMED:10574995, PUBMED:8606190] and the ATP binding cassette (ABC) transporter MsbA that flips the lipid A-core moiety from the inner leaflet to the outer leaflet of the IM [PUBMED:11278265, PUBMED:8809774, PUBMED:9575204]. O-antigen repeat units are then polymerised in the periplasm by the Wzy polymerase and ligated to the lipid A-core moiety by the WaaL ligase [see, PUBMED:12045108, PUBMED:18424520].
The LPS transport machinery is composed of LptA, LptB, LptC, LptD, LptE. This supported by the fact, that depletion of any of one of these proteins blocks the LPS assembly pathway and results in very similar OM biogenesis defects. Moreover, the location of at least one of these five proteins in every cellular compartment suggests a model for how the LPS assembly pathway is organised and ordered in space [PUBMED:18424520].
LptE forms a complex with LptD, which is involved in the assembly of LPS in the outer leaflet of the outer membrane [PUBMED:16861298, PUBMED:18424520, PUBMED:15192148]. LptE interacts with LptD while this protein is being assembled by the beta-barrel assembly machine [PUBMED:21257909]. In Neisseria, LptE does not have a direct role in LPS transport, suggesting that the Lpt system does not function in a completely conserved manner in all Gram-negative bacteria [PUBMED:21705335].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||outer membrane (GO:0019867)|
|Biological process||Gram-negative-bacterium-type cell outer membrane assembly (GO:0043165)|
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|Previous IDs:||DUF532; RplB;|
|Number in seed:||162|
|Number in full:||2176|
|Average length of the domain:||153.80 aa|
|Average identity of full alignment:||20 %|
|Average coverage of the sequence by the domain:||84.72 %|
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