<p>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 [<cite idref="PUB00025426"/>]. Members of this superfamily include macrophage migration inhibitory factor (MIF) and related proteins such as D-dopachrome tautomerase; 4-oxalocronoate tautomerase and related enzymes such as trans-3-chloroacrylic acid dehalogenase; and 5-carboxymethyl-2-hydroxymuconate isomerase (CHMI).</p><p> 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 [<cite idref="PUB00034437"/>]. 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 [<cite idref="PUB00034439"/>].</p><p>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 [<cite idref="PUB00007676"/>].</p><p>5-carboxymethyl-2-hydroxymuconate isomerase (CHMI) is a trimeric enzyme involved in the homoprotocatechuate pathway in <taxon tax_id="562">Escherichia coli</taxon> [<cite idref="PUB00019310"/>]. This enzyme catalyses the isomerisation of 5-carboxymethyl-2-hydroxymuconate (CHM) to 5-carboxymethyl-2-oxo-3-hexene-1,6-dioate (COHED).</p>