2fm7
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Evolution of Enzymatic Activity in the Tautomerase Superfamily: Mechanistic and Structural Consequences of the L8R Mutation in 4-Oxalocrotonate Tautomerase
OverviewOverview
4-Oxalocrotonate tautomerase (4-OT) and trans-3-chloroacrylic acid, dehalogenase (CaaD) are members of the tautomerase superfamily, a group of, structurally homologous proteins that share a beta-alpha-beta fold and a, catalytic amino-terminal proline. 4-OT, from Pseudomonas putida mt-2, catalyzes the conversion of 2-oxo-4-hexenedioate to 2-oxo-3-hexenedioate, through the dienol intermediate 2-hydroxymuconate in a catabolic pathway, for aromatic hydrocarbons. CaaD, from Pseudomonas pavonaceae 170, catalyzes the hydrolytic dehalogenation of trans-3-chloroacrylate in the, trans-1,3-dichloropropene degradation pathway. Both reactions may involve, an arginine-stabilized enediolate intermediate, a capability that may, partially account for the low-level CaaD activity of 4-OT. Two active-site, residues in 4-OT, Leu-8 and Ile-52, have now been mutated to the, positionally conserved and catalytic ones in CaaD, alphaArg-8, and, alphaGlu-52. The L8R and L8R/I52E mutants show improved CaaD activity (50-, and 32-fold increases in k(cat)/K(m), respectively) and diminished 4-OT, activity (5- and 1700-fold decreases in k(cat)/K(m), respectively). The, increased efficiency of L8R-4-OT for the CaaD reaction stems primarily, from an 8.8-fold increase in k(cat), whereas that of the L8R/I52E mutant, is due largely to a 23-fold decrease in K(m). The presence of the, additional arginine residue in the active site of L8R-4-OT does not alter, the pK(a) of the Pro-1 amino group from that measured for the wild type, (6.5 +/- 0.1 versus 6.4 +/- 0.2). Moreover, the crystal structure of, L8R-4-OT is comparable to that of the wild type. Hence, the enhanced CaaD, activity of L8R-4-OT is likely due to the additional arginine residue that, can participate in substrate binding and/or stabilization of the putative, enediolate intermediate. The results also suggest that the evolution of, new functions within the tautomerase superfamily could be quite facile, requiring only a few strategically placed active-site mutations.
About this StructureAbout this Structure
2FM7 is a Single protein structure of sequence from Pseudomonas putida with CL as ligand. Full crystallographic information is available from OCA.
ReferenceReference
Evolution of enzymatic activity in the tautomerase superfamily: mechanistic and structural consequences of the L8R mutation in 4-oxalocrotonate tautomerase., Poelarends GJ, Almrud JJ, Serrano H, Darty JE, Johnson WH Jr, Hackert ML, Whitman CP, Biochemistry. 2006 Jun 27;45(25):7700-8. PMID:16784221
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