|Gene:||kbl||Accession Numbers: EG10512 (MetaCyc), b3617, ECK3607|
Species: Escherichia coli K-12 substr. MG1655
Subunit composition of 2-amino-3-ketobutyrate CoA ligase = [Kbl]2
2-Amino-3-ketobutyrate CoA ligase (Kbl, AKB ligase) catalyzes the reversible, coenzyme A-dependent cleavage/condensation reaction between 2-amino-3-oxobutanoate (2-amino-3-ketobutyrate) and glycine plus acetyl-CoA. It is the second reaction in the threonine dehydrogenase-initiated pathway by which threonine is converted to glycine which is then converted to serine. This pathway is the primary route for threonine utilization in prokaryotes and is an alternate pathway for serine biosynthesis in E. coli [Mukherjee87, Ravnikar87]. Because 2-amino-3-oxobutanoate can spontaneously decarboxylate to aminoacetone, a second threonine dehydrogenase-initiated pathway is also possible (see L-threonine degradation III (to methylglyoxal)).
The crystal structure of Kbl in complex with a pyridoxal-5'-phosphate-substrate intermediate has been determined at 2.0 Å resolution and a reaction mechanism was proposed. Kbl belongs to the α family of PLP-dependent enzymes. It was noted that this enzyme has been evolutionarily conserved and E. coli Kbl shares 54% amino acid sequence identity with the human enzyme [Schmidt01]. Details of the condensation mechanism have been studied [Bashir06].
Review: Reitzer, L. (2005) "Catabolism of Amino Acids and Related Compounds" EcoSal 3.4.7 [ECOSAL]
|Map Position: [3,789,378 <- 3,790,574]|
Molecular Weight of Polypeptide: 43.117 kD (from nucleotide sequence), 42.0 kD (experimental) [Mukherjee87 ]
Molecular Weight of Multimer: 85.0 kD (experimental) [Mukherjee87]
Unification Links: ASAP:ABE-0011832 , CGSC:18205 , DIP:DIP-48030N , EchoBASE:EB0507 , EcoGene:EG10512 , EcoliWiki:b3617 , Mint:MINT-1315923 , ModBase:P0AB77 , OU-Microarray:b3617 , PortEco:kbl , PR:PRO_000023046 , Pride:P0AB77 , Protein Model Portal:P0AB77 , RefSeq:NP_418074 , RegulonDB:EG10512 , SMR:P0AB77 , String:511145.b3617 , UniProt:P0AB77
Relationship Links: InterPro:IN-FAMILY:IPR001917 , InterPro:IN-FAMILY:IPR004839 , InterPro:IN-FAMILY:IPR011282 , InterPro:IN-FAMILY:IPR015421 , InterPro:IN-FAMILY:IPR015422 , InterPro:IN-FAMILY:IPR015424 , PDB:Structure:1FC4 , Pfam:IN-FAMILY:PF00155 , Prosite:IN-FAMILY:PS00599
|Biological Process:||GO:0008152 - metabolic process
GO:0009058 - biosynthetic process [GOA01a]
GO:0019518 - L-threonine catabolic process to glycine [UniProtGOA12]
|Molecular Function:||GO:0016874 - ligase activity
GO:0030170 - pyridoxal phosphate binding [GOA01a, Mukherjee87, Schmidt01]
GO:0042803 - protein homodimerization activity [Mukherjee87]
GO:0046872 - metal ion binding [Mukherjee87]
GO:0003824 - catalytic activity [GOA01a]
GO:0008890 - glycine C-acetyltransferase activity [GOA01, GOA01a]
GO:0016740 - transferase activity [UniProtGOA11a, GOA01a]
GO:0016746 - transferase activity, transferring acyl groups [UniProtGOA11a]
|Cellular Component:||GO:0005737 - cytoplasm
GO:0005829 - cytosol [DiazMejia09, Ishihama08, LopezCampistrou05]
|MultiFun Terms:||metabolism → carbon utilization → amino acids|
|metabolism → central intermediary metabolism → threonine catabolism|
Enzymatic reaction of: 2-amino-3-ketobutyrate CoA ligase
Synonyms: glycine C-acetyltransferase, AKB ligase, aminoacetone synthase, aminoacetone synthetase, acetyl-CoA:glycine C-acetyltransferase
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 direction of enzyme catalysis.
This reaction is reversible. [Mukherjee87]
The enzyme activity was assayed in the reverse direction as the amount of coenzyme A released by the condensation of acetyl-CoA with glycine. No activity was seen with valeryl-CoA, succinyl-CoA, or glutaryl-CoA. The enzyme was specific for glycine and no activity was seen with glycinamide, glycine methylester, 2-aminoethanol, aminomethylphosphonic acid, aminomalonate, L-alanine, L-serine, L-threonine, L-valine, or L-leucine. Varying degrees of inhibition were seen with the divalent cations Mn2+, Ni2+ Ca2+ Sr2+ Ba2+ Zn2+ Hg2+ Cu2+ and Cd2+, with the latter three showing strongest inhibition [Mukherjee87].
The enzyme was also shown to have L-threonine aldolase activity, cleaving L-threonine to acetaldehyde and glycine. Although the Km for glycine (ligase activity) was 10 mM and the Km for L-threonine (aldolase activity) was 0.9 mM, the Vmax values were 2.5 μmol of CoA released/min per mg for the ligase activity versus 0.014 μmol of acetaldehyde formed (NADH oxidized)/min per mg for the aldolase activity [Marcus93].
Inhibitors (Unknown Mechanism): diacetyl [Mukherjee92] , cyclohexane-1,2-dione [Mukherjee92] , phenylglyoxal [Mukherjee92] , 4-(oxoacetyl)phenoxyacetate [Mukherjee92] , Hg2+ [Mukherjee87] , Cu2+ [Mukherjee87] , Cd2+ [Mukherjee87] , L-cysteine [Mukherjee87] , dithiothreitol [Mukherjee87] , glutathione [Mukherjee87] , aminomethylphosphonate [Mukherjee87] , coenzyme A [Comment 4]
|Protein-Segment||111 -> 112|
|Protein-Segment||210 -> 213|
|Protein-Segment||241 -> 244|
|Protein-Segment||274 -> 275|
10/20/97 Gene b3617 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG10512.
Bashir06: Bashir Q, Rashid N, Akhtar M (2006). "Mechanism and substrate stereochemistry of 2-amino-3-oxobutyrate CoA ligase: implications for 5-aminolevulinate synthase and related enzymes." Chem Commun (Camb) (48);5065-7. PMID: 17146529
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
LopezCampistrou05: Lopez-Campistrous A, Semchuk P, Burke L, Palmer-Stone T, Brokx SJ, Broderick G, Bottorff D, Bolch S, Weiner JH, Ellison MJ (2005). "Localization, annotation, and comparison of the Escherichia coli K-12 proteome under two states of growth." Mol Cell Proteomics 4(8);1205-9. PMID: 15911532
Marcus93: Marcus JP, Dekker EE (1993). "Identity and some properties of the L-threonine aldolase activity manifested by pure 2-amino-3-ketobutyrate ligase of Escherichia coli." Biochim Biophys Acta 1164(3);299-304. PMID: 8343529
Mukherjee87: Mukherjee JJ, Dekker EE (1987). "Purification, properties, and N-terminal amino acid sequence of homogeneous Escherichia coli 2-amino-3-ketobutyrate CoA ligase, a pyridoxal phosphate-dependent enzyme." J Biol Chem 1987;262(30);14441-7. PMID: 3117785
Mukherjee90: Mukherjee JJ, Dekker EE (1990). "2-Amino-3-ketobutyrate CoA ligase of Escherichia coli: stoichiometry of pyridoxal phosphate binding and location of the pyridoxyllysine peptide in the primary structure of the enzyme." Biochim Biophys Acta 1990;1037(1);24-9. PMID: 2104756
Mukherjee92: Mukherjee JJ, Dekker EE (1992). "Inactivation of Escherichia coli 2-amino-3-ketobutyrate CoA ligase by phenylglyoxal and identification of an active-site arginine peptide." Arch Biochem Biophys 299(1);147-53. PMID: 1444446
Rex91: Rex JH, Aronson BD, Somerville RL (1991). "The tdh and serA operons of Escherichia coli: mutational analysis of the regulatory elements of leucine-responsive genes." J Bacteriol 173(19);5944-53. PMID: 1917830
Schmidt01: Schmidt A, Sivaraman J, Li Y, Larocque R, Barbosa JA, Smith C, Matte A, Schrag JD, Cygler M (2001). "Three-dimensional structure of 2-amino-3-ketobutyrate CoA ligase from Escherichia coli complexed with a PLP-substrate intermediate: inferred reaction mechanism." Biochemistry 40(17);5151-60. PMID: 11318637
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