|Gene:||metE||Accession Numbers: EG10584 (MetaCyc), b3829, ECK3823|
Species: Escherichia coli K-12 substr. MG1655
In the absence of exogenously supplied vitamin B12 (cobalamin), E. coli MetE catalyzes the final step of de novo methionine biosynthesis. In the presence of the vitamin B12 cofactor, MetH functions in this reaction and synthesis of MetE is repressed (see pathway L-methionine biosynthesis I). The metE and metH genes lack similarity in their deduced amino acid sequences, suggesting that these proteins arose by convergent evolution [Gonzalez92].
MetE was shown to utilize only the triglutamate form of folate (5-methyltetrahydropteroyltri-L-glutamate) whereas MetH utilized either the monoglutamate (5-methyl-tetrahydrofolate) or the triglutamate forms of folate [Foster64].
Early studies utilized unpurified or partially purified enzyme [Foster64, Guest64]. The enzyme was later purified from extracts of E. coli K-12 and characterized [Whitfield70]. The metE gene was cloned and expressed [Chu85, Old88] and the expression of MetE was shown to be repressed by methionine and vitamin B12 [Old88]. Recombinant enzyme has also been purified and characterized [Gonzalez92].
MetE contains zinc which is necessary for its activity. Cys643 and Cys726 have been identified as two of the zinc ligands and a third may be His641 [Zhou99]. Evidence suggested that the sulfur of the homocysteine substrate binds directly to the zinc ion [Peariso01]. Modeling of the structure of E. coli MetE based on the crystal structure of MetE from Thermotoga maritima showed a double-barrel structure that likely evolved by gene duplication [Pejchal05a].
Inactivation of MetE has been shown in E. coli cells growing under conditions of transient oxidative stress, resulting in a methionine auxotrophy. Under these conditions MetE protein is found at high levels. A possible mechanism involving reversible inactivation of MetE by oxidized glutathione was proposed and glutathionylation of Cys645 at the entrance to the active site was demonstrated. Thiol-trapping experiments provided direct evidence of MetE oxidation in vivo [Hondorp04]. It was subsequently shown that a Cys645Ala mutant eliminated the methionine auxotrophy imposed by oxidative stress, suggesting that modulation of MetE activity by Cys645 oxidation has physiological significance under these conditions. Control of methionine availability may modulate cellular growth during oxidative stress [Hondorp09].
The MetE reaction mechanism has been studied with respect to the kinetic pathway for binding of substrates 5-methyltetrahydropteroyltri-L-glutamate and homocysteine. Binding of these substrates was found to be synergistic. Evidence also suggested that activation of 5-methyltetrahydropteroyltri-L-glutamate for methyl group transfer occurs by protonation of N5, which occurs upon formation of the ternary MetE, homocysteine, 5-methyltetrahydropteroyltri-L-glutamate complex [Taurog06a, Taurog06].
Adaptation of E. coli to anaerobic growth has been shown to involve the action of a conserved, anaerobically induced small regulatory RNA named FnrS which negatively regulates a set of genes that includes metE (see the illustration above and click on FnrS). FnrS expression is strictly dependent on the anaerobic transcriptional regulator FNR. It was suggested that FnrS-mediated post-transcriptional control may play a role in rapid adaptation during anaerobic-to-aerobic transitions [Boysen10].
MetJ and MetR are involved in the overexpression of MetE, which is strongly induced by GroE depletion [Fujiwara12].
Review: Hondrop, E.R. and R.G. Matthews (2006) "Methionine" EcoSal 220.127.116.11 [ECOSAL].
|Map Position: [4,011,076 -> 4,013,337]|
Molecular Weight of Polypeptide: 84.673 kD (from nucleotide sequence)
Unification Links: ASAP:ABE-0012520 , CGSC:512 , DIP:DIP-6847N , EchoBASE:EB0579 , EcoGene:EG10584 , EcoliWiki:b3829 , Mint:MINT-1280694 , OU-Microarray:b3829 , PortEco:metE , PR:PRO_000023211 , Pride:P25665 , Protein Model Portal:P25665 , RefSeq:NP_418273 , RegulonDB:EG10584 , SMR:P25665 , String:511145.b3829 , Swiss-Model:P25665 , UniProt:P25665
Instance reaction of [L-homocysteine + an N5-methyl-tetrahydrofolate → L-methionine + a tetrahydrofolate] (18.104.22.168):
|Biological Process:||GO:0008652 - cellular amino acid biosynthetic process
GO:0009086 - methionine biosynthetic process [UniProtGOA11, GOA06, GOA01]
GO:0032259 - methylation [UniProtGOA11]
|Molecular Function:||GO:0003871 - 5-methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase activity
[GOA06, GOA01a, GOA01, Whitfield70]
GO:0005515 - protein binding [Rajagopala14, Arifuzzaman06]
GO:0008270 - zinc ion binding [GOA01, Zhou99]
GO:0008168 - methyltransferase activity [UniProtGOA11]
GO:0016740 - transferase activity [UniProtGOA11]
GO:0046872 - metal ion binding [UniProtGOA11]
|Cellular Component:||GO:0005829 - cytosol [DiazMejia09, Ishihama08]|
|MultiFun Terms:||metabolism → biosynthesis of building blocks → amino acids → methionine|
Enzymatic reaction of: cobalamin-independent homocysteine transmethylase
Synonyms: methionine synthase, tetrahydropteroyltriglutamate methyltransferase, homocysteine methylase, 5-methyltetrahydropteroyltri-L-glutamate:L-homocysteine S-methyltransferase, cobalamin-independent methionine synthase, 5-methyltetrahydropteroyltriglutamate-homocysteine-S-methyltransferase, 5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferase, 5-methyltetrahydropteroyltriglutamate-homocysteine transmethylase
EC Number: 22.214.171.124
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.
This reaction is reversible.
In Pathways: superpathway of S-adenosyl-L-methionine biosynthesis , aspartate superpathway , superpathway of L-lysine, L-threonine and L-methionine biosynthesis I , superpathway of L-methionine biosynthesis (transsulfuration) , L-homoserine and L-methionine biosynthesis , L-methionine biosynthesis I
Enzyme activity required the presence of inorganic phosphate in the reaction mixture and was stimulated by the divalent cations Mg2+ or Mn2+. Ca2+ was less effective and Ba2+ Co2+ Fe2+ and Zn2+ were not effective. Enzyme activity was nonspecifically inhibited by high ionic strength. Monoglutamate and diglutamate folate derivatives could not replace the triglutamate folate derivative as a methyl donor. Cysteine, β-mercaptoethanol, or dithiothreitol could not replace homocysteine as a methyl acceptor [Whitfield70, Guest64].
|Repeat||2 -> 370|
|Chain||2 -> 753|
|Repeat||371 -> 753|
10/20/97 Gene b3829 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG10584; confirmed by SwissProt match.
Arifuzzaman06: Arifuzzaman M, Maeda M, Itoh A, Nishikata K, Takita C, Saito R, Ara T, Nakahigashi K, Huang HC, Hirai A, Tsuzuki K, Nakamura S, Altaf-Ul-Amin M, Oshima T, Baba T, Yamamoto N, Kawamura T, Ioka-Nakamichi T, Kitagawa M, Tomita M, Kanaya S, Wada C, Mori H (2006). "Large-scale identification of protein-protein interaction of Escherichia coli K-12." Genome Res 16(5);686-91. PMID: 16606699
Boysen10: Boysen A, Moller-Jensen J, Kallipolitis B, Valentin-Hansen P, Overgaard M (2010). "Translational regulation of gene expression by an anaerobically induced small non-coding RNA in Escherichia coli." J Biol Chem 285(14);10690-702. PMID: 20075074
Chu85: Chu J, Shoeman R, Hart J, Coleman T, Mazaitis A, Kelker N, Brot N, Weissbach H (1985). "Cloning and expression of the metE gene in Escherichia coli." Arch Biochem Biophys 239(2);467-74. PMID: 2988449
Daniels92: Daniels DL, Plunkett G, Burland V, Blattner FR (1992). "Analysis of the Escherichia coli genome: DNA sequence of the region from 84.5 to 86.5 minutes." Science 1992;257(5071);771-8. PMID: 1379743
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
Gonzalez92: Gonzalez JC, Banerjee RV, Huang S, Sumner JS, Matthews RG (1992). "Comparison of cobalamin-independent and cobalamin-dependent methionine synthases from Escherichia coli: two solutions to the same chemical problem." Biochemistry 1992;31(26);6045-56. PMID: 1339288
Gonzalez96: Gonzalez JC, Peariso K, Penner-Hahn JE, Matthews RG (1996). "Cobalamin-independent methionine synthase from Escherichia coli: a zinc metalloenzyme." Biochemistry 35(38);12228-34. PMID: 8823155
Guest64: Guest JR, Friedman S, Foster MA, Tejerina G, Woods DD (1964). "Transfer of the methyl group from N5-methyltetrahydrofolates to homocysteine in Escherichia coli." Biochem J 92(3);497-504. PMID: 5319972
Hondorp09: Hondorp ER, Matthews RG (2009). "Oxidation of cysteine 645 of cobalamin-independent methionine synthase causes a methionine limitation in Escherichia coli." J Bacteriol 191(10);3407-10. PMID: 19286805
Link97: Link AJ, Robison K, Church GM (1997). "Comparing the predicted and observed properties of proteins encoded in the genome of Escherichia coli K-12." Electrophoresis 18(8);1259-313. PMID: 9298646
Neidhardt96: Neidhardt FC, Curtiss III R, Ingraham JL, Lin ECC, Low Jr KB, Magasanik B, Reznikoff WS, Riley M, Schaechter M, Umbarger HE "Escherichia coli and Salmonella, Cellular and Molecular Biology, Second Edition." American Society for Microbiology, Washington, D.C., 1996.
Old88: Old IG, Hunter MG, Wilson DT, Knight SM, Weatherston CA, Glass RE (1988). "Cloning and characterization of the genes for the two homocysteine transmethylases of Escherichia coli." Mol Gen Genet 211(1);78-87. PMID: 2830470
Peariso01: Peariso K, Zhou ZS, Smith AE, Matthews RG, Penner-Hahn JE (2001). "Characterization of the zinc sites in cobalamin-independent and cobalamin-dependent methionine synthase using zinc and selenium X-ray absorption spectroscopy." Biochemistry 40(4);987-93. PMID: 11170420
Plunkett93: Plunkett G, Burland V, Daniels DL, Blattner FR (1993). "Analysis of the Escherichia coli genome. III. DNA sequence of the region from 87.2 to 89.2 minutes." Nucleic Acids Res 1993;21(15);3391-8. PMID: 8346018
Rajagopala14: Rajagopala SV, Sikorski P, Kumar A, Mosca R, Vlasblom J, Arnold R, Franca-Koh J, Pakala SB, Phanse S, Ceol A, Hauser R, Siszler G, Wuchty S, Emili A, Babu M, Aloy P, Pieper R, Uetz P (2014). "The binary protein-protein interaction landscape of Escherichia coli." Nat Biotechnol 32(3);285-90. PMID: 24561554
Taurog06a: Taurog RE, Jakubowski H, Matthews RG (2006). "Synergistic, random sequential binding of substrates in cobalamin-independent methionine synthase." Biochemistry 45(16);5083-91. PMID: 16618097
Whitfield70: Whitfield CD, Steers EJ, Weisbach H (1970). "Purification and properties of 5-methyltetrahydropteroyltriglutamate-homocysteine transmethylase." J Biol Chem 1970;245(2);390-401. PMID: 4904482
Zhou00a: Zhou ZS, Smith AE, Matthews RG (2000). "L-Selenohomocysteine: one-step synthesis from L-selenomethionine and kinetic analysis as substrate for methionine synthases." Bioorg Med Chem Lett 10(21);2471-5. PMID: 11078203
Zhou99: Zhou ZS, Peariso K, Penner-Hahn JE, Matthews RG (1999). "Identification of the zinc ligands in cobalamin-independent methionine synthase (MetE) from Escherichia coli." Biochemistry 1999;38(48);15915-26. PMID: 10625458
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