spacer
View the latest EBI news stories and important announcements...
more

spacer
Search The CSA
PDB ID
UNIPROT ID
EC Number

Catalytic Site Atlas

CSA LITERATURE entry for 1fc4

E.C. nameglycine C-acetyltransferase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 2.3.1.29
CSA Homologues of 1fc4There are 93 Homologs
CSA Entries With UniProtID P0AB77
CSA Entries With EC Number 2.3.1.29
PDBe Entry 1fc4
PDBSum Entry 1fc4
MACiE Entry 1fc4

Literature Report

IntroductionThreonine is degraded into glycine and the acetyl group in a pathway common to prokaryotic and eukaryotic cells. The pathway is two steps long; the first step is the oxidation of the hydroxy group of threonine to create 2-amino-3-ketobutyrate. The second step is catalysed by 2-amino-3-ketobutyrate CoA ligase (KBL); this is a PLP-dependent acetyltransferase, transferring the newly formed acetyl group of the substrate to Coenzyme A to give glycine and acetyl-CoA.
The two enzymes needed for the pathway form a complex; this is because the aminoketobutyrate intermediate (substrate for KBL) spontaneously decarboxylates in aqueous solution.
Mechansim1) Lys 244 has a Schiff base linkage with the PLP cofactor. It is displaced by the amino acid substrate, in the usual fashion to give an external aldimine (PLP and threonine with a Schiff base linkage). In these steps His 213 acts as a general acid to the phenolic oxygen of PLP (with the phenolic proton being transferred to Lys 244), and a general base to the amino group of the joining threonine.
2) The thiol of CoA is nucleophilic and attacks the carbon of the carbonyl group of the aldimine. This gives a tetrahedral intermediate where the oxyanion is stabilised by hydrogen bonding to Ser 185. Lys 244 deprotonates the sulphur atom.
3) The tetrahedral intermediate collapses to release acetyl-CoA. The glycine moiety and PLP are held in a quinoid intermediate.
4) Lys 244 protonates the nitrogen of the glycine moiety, regenerating the substrate-PLP Schiff base link.
5) Lys 244 displaces the group bound to PLP in the usual fashion (His 213 again acting as a general acid/base) to release glycine and regenerate the original active PLP-enzyme adduct.
Reaction

Catalytic Sites for 1fc4

Annotated By Reference To The Literature - Site 5 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA213213macie:sideChainHis 213 acts as a general acid and base during the steps where the PLP Schiff base linkage is transferred from Lys 244 to the amino acid, and vice versa.
LysA244244macie:sideChainLys 244 is Schiff base-linked to the PLP cofactor in the resting state, and displaces the glycine product in the last step of the reaction.
Lys 244 deprotonates the thiol after the formation of the tetrahedral intermediate. The proton is transferred to the nitrogen atom of the glycine moiety of the quinoid intermediate to regenerate the imine linkage.

Annotated By Reference To The Literature - Site 6 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisB213213macie:sideChainHis 213 acts as a general acid and base during the steps where the PLP Schiff base linkage is transferred from Lys 244 to the amino acid, and vice versa.
LysB244244macie:sideChainLys 244 is Schiff base-linked to the PLP cofactor in the resting state, and displaces the glycine product in the last step of the reaction.
Lys 244 deprotonates the thiol after the formation of the tetrahedral intermediate. The proton is transferred to the nitrogen atom of the glycine moiety of the quinoid intermediate to regenerate the imine linkage.

Literature References

Notes:Although the active site runs between the monomers, the catalytic residues only come from one of the monomers.
Schmidt A
Three-dimensional structure of 2-amino-3-ketobutyrate CoA ligase from Escherichia coli complexed with a PLP-substrate intermediate: inferred reaction mechanism.
Biochemistry 2001 40 5151-5160
PubMed: 11318637
spacer
spacer