|Gene:||lapB||Accession Numbers: EG12691 (EcoCyc), b1280, ECK1275|
Biochemical and genetic analyses suggest that the LapB inner membrane protein functions in the coupling of lipopolysaccharide (LPS) biosynthesis and transport.
lapB (formerly yciM) is essential for growth under standard laboratory conditions. Absence of lapB results in increased LPS production and cell death. Overexpression of lapB results in decreased LPS levels [Mahalakshmi14]. The viability of the lapB mutant from the Keio collection is due to the presence of a suppressor mutation in lpxC [Mahalakshmi14].
Suppressor free ΔlapB mutants can be constructed on minimal medium at 30°C. LPS extracted from these mutants contains increased amounts of precursor forms and various defects in (KDO)2-lipid A structure: carbon chain length polymorphism, pentaacylation and derivatives with two lauroyl side chains [Klein14]. ΔlapB mutants also have increased levels of LpxC [Klein14].
Mutations in lpxA, lpxC and lpxD which result in decreased lipid IVA synthesis, suppress the essentiality of lapB [Mahalakshmi14]. Extragenic suppressors of lapB essentiality map to genes involved in Lipid A core biosynthesis (waaC, waaQ, waaG) and heptose biosynthesis (lpcA); multicopy suppressors of lapB essentiality include fabZ, fabB (phospholipid and fatty acid biosynthesis), murA (peptidoglycan synthesis), rcsF, hicA, a new small RNA (slrA) and genes of unknown function (yceK, yeaD, nudK, mliC) [Klein14]. A null mutation in lpp which encodes murein lipoprotein, suppresses the essentiality of lapB [Klein14].
LapB is anchored to the cytoplasmic membrane by it's N-terminus with the remainder of the protein located in the cytoplasm. The membrane anchor is essential for LapB function.LapB contains an iron-sulfur center (rubredoxin type) coordinated by 4 cysteine residues located at the C-terminus of the protein. LapB binds zinc in a 1:1 stoichiometry in vitro but is predicted to bind iron in vivo [Nicolaes14]. LapB contains six tetratricopeptide (TPR) repeats and a C-terminal Zinc-finger domain [Mahalakshmi14].
LapB copurifies with LapA, FtsH and WaaC and with the LPS transport system proteins (LptE/D, LptBFGC, LptA). Purified LapB contains LPS [Klein14].
lapAB transcription is subject to heat shock induction via an RpoH-regulated promoter located upstream of lapA [Klein14]. LapB is a post-transcriptional regulator of LpxC - this regulation is dependent on the presence of the FtsH protease [Mahalakshmi14].
lapB: lipopolysaccharide assembly protein B
Gene Citations: [Nonaka06]
Locations: cytosol, inner membrane
|Map Position: [1,338,582 -> 1,339,751] (28.85 centisomes)||Length: 1170 bp / 389 aa|
Molecular Weight of Polypeptide: 44.531 kD (from nucleotide sequence), 55.0 kD (experimental) [Nicolaes14 ]
Unification Links: ASAP:ABE-0004300 , DIP:DIP-48161N , EchoBASE:EB2554 , EcoGene:EG12691 , EcoliWiki:b1280 , ModBase:P0AB58 , OU-Microarray:b1280 , PortEco:yciM , Protein Model Portal:P0AB58 , RefSeq:NP_415796 , RegulonDB:EG12691 , SMR:P0AB58 , String:511145.b1280 , UniProt:P0AB58
Relationship Links: InterPro:IN-FAMILY:IPR011990 , InterPro:IN-FAMILY:IPR013026 , InterPro:IN-FAMILY:IPR013105 , InterPro:IN-FAMILY:IPR019734 , Pfam:IN-FAMILY:PF07719 , Pfam:IN-FAMILY:PF13176 , Prosite:IN-FAMILY:PS50005 , Prosite:IN-FAMILY:PS50293 , Smart:IN-FAMILY:SM00028
|Biological Process:||GO:0008653 - lipopolysaccharide metabolic process [Klein14, Mahalakshmi14]|
|Molecular Function:||GO:0046872 - metal ion binding [UniProtGOA11a, Nicolaes14]|
|Cellular Component:||GO:0005829 - cytosol
GO:0005887 - integral component of plasma membrane [Nicolaes14]
GO:0005886 - plasma membrane [UniProtGOA11, UniProtGOA11a]
GO:0016020 - membrane [UniProtGOA11a]
GO:0016021 - integral component of membrane [UniProtGOA11a]
|MultiFun Terms:||metabolism → biosynthesis of macromolecules (cellular constituents) → lipopolysaccharide|
|Growth Medium||Growth?||T (°C)||O2||pH||Osm/L||Growth Observations|
|LB enriched||Yes||37||Aerobic||6.95||Yes [Gerdes03, Comment 1]|
|LB Lennox||Indeterminate||37||Aerobic||7||Yes [Baba06, Comment 2] |
|M9 medium with 1% glycerol||Yes||37||Aerobic||7.2||0.35||Yes [Joyce06, Comment 3]|
|MOPS medium with 0.4% glucose||Yes||37||Aerobic||7.2||0.22||Yes [Baba06, Comment 2]|
|Signal-Sequence||1 -> 16|
|Chain||17 -> 389|
|Repeat||69 -> 102|
|Repeat||107 -> 140|
|Repeat||141 -> 174|
|Repeat||180 -> 213|
|Repeat||214 -> 247|
|Repeat||249 -> 282|
|Zn-Finger-Region||357 -> 374|
10/20/97 Gene b1280 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG12691; confirmed by SwissProt match.
Baba06: Baba T, Ara T, Hasegawa M, Takai Y, Okumura Y, Baba M, Datsenko KA, Tomita M, Wanner BL, Mori H (2006). "Construction of Escherichia coli K-12 in-frame, single-gene knockout mutants: the Keio collection." Mol Syst Biol 2;2006.0008. PMID: 16738554
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Gerdes03: Gerdes SY, Scholle MD, Campbell JW, Balazsi G, Ravasz E, Daugherty MD, Somera AL, Kyrpides NC, Anderson I, Gelfand MS, Bhattacharya A, Kapatral V, D'Souza M, Baev MV, Grechkin Y, Mseeh F, Fonstein MY, Overbeek R, Barabasi AL, Oltvai ZN, Osterman AL (2003). "Experimental determination and system level analysis of essential genes in Escherichia coli MG1655." J Bacteriol 185(19);5673-84. PMID: 13129938
Joyce06: Joyce AR, Reed JL, White A, Edwards R, Osterman A, Baba T, Mori H, Lesely SA, Palsson BO, Agarwalla S (2006). "Experimental and computational assessment of conditionally essential genes in Escherichia coli." J Bacteriol 188(23);8259-71. PMID: 17012394
Mahalakshmi14: Mahalakshmi S, Sunayana MR, SaiSree L, Reddy M (2014). "yciM is an essential gene required for regulation of lipopolysaccharide synthesis in Escherichia coli." Mol Microbiol 91(1);145-57. PMID: 24266962
Nicolaes14: Nicolaes V, El Hajjaji H, Davis RM, Van der Henst C, Depuydt M, Leverrier P, Aertsen A, Haufroid V, Ollagnier de Choudens S, De Bolle X, Ruiz N, Collet JF (2014). "Insights into the function of YciM, a heat shock membrane protein required to maintain envelope integrity in Escherichia coli." J Bacteriol 196(2);300-9. PMID: 24187084
Nonaka06: Nonaka G, Blankschien M, Herman C, Gross CA, Rhodius VA (2006). "Regulon and promoter analysis of the E. coli heat-shock factor, sigma32, reveals a multifaceted cellular response to heat stress." Genes Dev 20(13);1776-89. PMID: 16818608
ParadisBleau14: Paradis-Bleau C, Kritikos G, Orlova K, Typas A, Bernhardt TG (2014). "A genome-wide screen for bacterial envelope biogenesis mutants identifies a novel factor involved in cell wall precursor metabolism." PLoS Genet 10(1);e1004056. PMID: 24391520
Zhang07: Zhang N, Chen R, Young N, Wishart D, Winter P, Weiner JH, Li L (2007). "Comparison of SDS- and methanol-assisted protein solubilization and digestion methods for Escherichia coli membrane proteome analysis by 2-D LC-MS/MS." Proteomics 7(4);484-93. PMID: 17309111
Wade06: Wade JT, Roa DC, Grainger DC, Hurd D, Busby SJ, Struhl K, Nudler E (2006). "Extensive functional overlap between sigma factors in Escherichia coli." Nat Struct Mol Biol 13(9);806-14. PMID: 16892065
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