Structural and kinetic characterization of two 4-oxalocrotonate tautomerases in Methylibium petroleiphilum strain PM1.Terrell, C.R., Burks, E.A., Whitman, C.P., Hoffman, D.W.
(2013) Arch Biochem Biophys 537: 113-124
- PubMed: 23831510
- DOI: https://doi.org/10.1016/j.abb.2013.06.016
- Primary Citation of Related Structures:
- PubMed Abstract:
Methylibium petroleiphilum strain PM1 uses various petroleum products including the fuel additive methyl tert-butyl ether and straight chain and aromatic hydrocarbons as sole carbon and energy sources. It has two operons, dmpI and dmpII, that code for the enzymes in a pair of parallel meta-fission pathways. In order to understand the roles of the pathways, the 4-oxalocrotonate tautomerase (4-OT) isozyme from each pathway was characterized. Tautomerase I and tautomerase II have the lowest pairwise sequence identity (35%) among the isozyme pairs in the parallel pathways, and could offer insight into substrate preferences and pathway functions. The kinetic parameters of tautomerase I and tautomerase II were determined using 2-hydroxymuconate and 5-(methyl)-2-hydroxymuconate. Both tautomerase I and tautomerase II process the substrates, but with different efficiencies. Crystal structures were determined for both tautomerase I and tautomerase II, at 1.57 and 1.64Å resolution, respectively. The backbones of tautomerase I and tautomerase II are highly similar, but have distinct active site environments. The results, in combination with those for other structurally and kinetically characterized 4-OT isozymes, suggest that tautomerase I catalyzes the tautomerization of both 2-hydroxymuconate and alkyl derivatives, whereas tautomerase II might specialize in other aromatic hydrocarbon metabolites.
Department of Chemistry and Biochemistry, University of Texas, Austin, 78712, USA.