4-Oxalocrotonate tautomerase

4-Oxalocrotonate tautomerase (EC 5.3.2.6) or 4-OT is an enzyme that converts 2-hydroxymuconate to the αβ-unsaturated ketone, 2-oxo-3-hexenedioate.^[1] This enzyme forms part of a bacterial metabolic pathway that oxidatively catabolizes toluene, o-xylene, 3-ethyltoluene, and 1,2,4-trimethylbenzene into intermediates of the citric acid cycle. With a monomer size of just 62 amino acid residues, the 4-Oxalocrotonate tautomerase is one of the smallest enzyme subunits known.^[2] However, in solution, the enzyme forms a hexamer of six identical subunits, so the active site may be formed by amino acid residues from several subunits.^[3] This enzyme is also unusual in that it uses a proline residue at the amino terminus as an active site residue.

Reaction catalyzed by 4-oxalocrotonate tautomerase.^[1]

4-oxalocrotonate tautomerase
Pseudomonas putida 4-oxalocrotonate tautomerase hexamer bound to 2-oxo-3-pentenoic acid. PDB: 1BJP​
Identifiers
Symbol	Taut
Pfam	PF01361
InterPro	IPR004370
CDD	cd00491
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary PDB PDB: 1bjp​ PDB: 1gyj​ PDB: 1gyx​ PDB: 1gyy​ PDB: 1otf​ PDB: 1s0y​ PDB: 4ota​ PDB: 4otb​ PDB: 4otc​

References

1. Chen LH, Kenyon GL, Curtin F, Harayama S, Bembenek ME, Hajipour G, Whitman CP (September 1992). "4-Oxalocrotonate tautomerase, an enzyme composed of 62 amino acid residues per monomer". The Journal of Biological Chemistry. 267 (25): 17716–21. PMID 1339435.
2. Whitman CP (June 2002). "The 4-oxalocrotonate tautomerase family of enzymes: how nature makes new enzymes using a beta-alpha-beta structural motif". Archives of Biochemistry and Biophysics. 402 (1): 1–13. doi:10.1016/S0003-9861(02)00052-8. PMID 12051677.
3. Subramanya HS, Roper DI, Dauter Z, Dodson EJ, Davies GJ, Wilson KS, Wigley DB (January 1996). "Enzymatic ketonization of 2-hydroxymuconate: specificity and mechanism investigated by the crystal structures of two isomerases". Biochemistry. 35 (3): 792–802. doi:10.1021/bi951732k. PMID 8547259.