title: Structural and kinetic characterization of two 4-oxalocrotonate tautomerases in Methylibium petroleiphilum strain PM1.
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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas, Austin, 78712, USA.
authors.forename: Cassidy R
authors.initials: CR
authors.lastname: Terrell
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Burks
authors.forename: Christian P
authors.initials: CP
authors.lastname: Whitman
authors.forename: David W
authors.initials: DW
authors.lastname: Hoffman
mesh_terms: D000595:Amino Acid Sequence; D020562:Betaproteobacteria / Q000145:classification* / Q000201:enzymology*; D004789:Enzyme Activation; D004795:Enzyme Stability; D007535:Isomerases / Q000737:chemistry* / Q000648:ultrastructure*; D007700:Kinetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013045:Species Specificity; D013379:Substrate Specificity
chemical_list: C021918:4-oxalocrotonate tautomerase; D007535:Isomerases
keywords: Bioremediation; Methylibium petroleiphilum; Tautomerase; X-ray crystallography