InterPro domain: IPR014347

Tautomerase superfamily members have a (beta-alpha-beta)2 structure in two layers, and use a similar mechanism of action involving an amino-terminal proline as a general base in a ket-enol tautomerisation reaction [ 1 ]. Members of this superfamily include macrophage migration inhibitory factor (MIF) and related proteins such as D-dopachrome tautomerase; 4-oxalocrotonoate tautomerase and related enzymes such as trans-3-chloroacrylic acid dehalogenase; and 5-carboxymethyl-2-hydroxymuconate Delta-isomerase (CHMI).

Macrophage migration inhibitory factor (MIF) is a key regulatory cytokine within innate and adaptive immune responses, capable of promoting and modulating the magnitude of the response [ 2 ]. MIF is released from T-cells and macrophages, and it can regulate cytokine secretion and the expression of receptors involved in the immune response. MIF has been linked to various inflammatory diseases, such as rheumatoid arthritis and atherosclerosis [ 3 ].

4-Oxalocrotonate tautomerase (4-OT) is a plasmid-encoded enzyme that catalyzes the isomerisation of beta,gamma-unsaturated enones to their alpha,beta-isomers. This enzyme is part of the plasmid-encoded catechol meta-fission pathway, which enables the bacteria to use various aromatic hydrocarbons as their sole sources of carbon and energy [ 4 ].

5-carboxymethyl-2-hydroxymuconate isomerase (CHMI) is a trimeric enzyme involved in the homoprotocatechuate pathway in Escherichia coli [ 5 ]. This enzyme catalyses the isomerisation of 5-carboxymethyl-2-hydroxymuconate (CHM) to 5-carboxymethyl-2-oxo-3-hexene-1,6-dioate (COHED).

1. The crystal structure of YdcE, a 4-oxalocrotonate tautomerase homologue from Escherichia coli, confirms the structural basis for oligomer diversity. Biochemistry 41, 12010-24
2. Macrophage migration inhibitory factor: molecular, cellular and genetic aspects of a key neuroendocrine molecule. J. Endocrinol. 182, 1-9
3. MIF: a new cytokine link between rheumatoid arthritis and atherosclerosis. null 5, 399-410
4. The 4-oxalocrotonate tautomerase family of enzymes: how nature makes new enzymes using a beta-alpha-beta structural motif. Arch. Biochem. Biophys. 402, 1-13
5. Enzymatic ketonization of 2-hydroxymuconate: specificity and mechanism investigated by the crystal structures of two isomerases. Biochemistry 35, 792-802