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The catalytic mechanism of the hotdog-fold enzyme superfamily 4-hydroxybenzoyl-CoA thioesterase from Arthrobacter sp. strain SU.

ABSTRACT: The hotdog-fold enzyme 4-hydroxybenzoyl-coenzyme A (4-HB-CoA) thioesterase from Arthrobacter sp. strain AU catalyzes the hydrolysis of 4-HB-CoA to form 4-hydroxybenzoate (4-HB) and coenzyme A (CoA) in the final step of the 4-chlorobenzoate dehalogenation pathway. Guided by the published X-ray structures of the liganded enzyme (Thoden, J. B., Zhuang, Z., Dunaway-Mariano, D., and Holden H. M. (2003) J. Biol. Chem. 278, 43709-43716), a series of site-directed mutants were prepared for testing the roles of active site residues in substrate binding and catalysis. The mutant thioesterases were subjected to X-ray structure determination to confirm retention of the native fold, and in some cases, to reveal changes in the active site configuration. In parallel, the wild-type and mutant thioesterases were subjected to transient and steady-state kinetic analysis, and to (18)O-solvent labeling experiments. Evidence is provided that suggests that Glu73 functions in nucleophilic catalysis, that Gly65 and Gln58 contribute to transition-state stabilization via hydrogen bond formation with the thioester moiety and that Thr77 orients the water nucleophile for attack at the 4-hydroxybenzoyl carbon of the enzyme-anhydride intermediate. The replacement of Glu73 with Asp was shown to switch the function of the carboxylate residue from nucleophilic catalysis to base catalysis and thus, the reaction from a two-step process involving a covalent enzyme intermediate to a single-step hydrolysis reaction. The E73D/T77A double mutant regained most of the catalytic efficiency lost in the E73D single mutant. The results from (31)P NMR experiments indicate that the substrate nucleotide unit is bound to the enzyme surface. Kinetic analysis of site-directed mutants was carried out to determine the contributions made by Arg102, Arg150, Ser120, and Thr121 in binding the nucleotide unit. Lastly, we show by kinetic and X-ray analyses of Asp31, His64, and Glu78 site-directed mutants that these three active site residues are important for productive binding of the substrate 4-hydroxybenzoyl ring.

SUBMITTER: Song F

PROVIDER: S-EPMC4710518 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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The catalytic mechanism of the hotdog-fold enzyme superfamily 4-hydroxybenzoyl-CoA thioesterase from Arthrobacter sp. strain SU.

Song Feng F Thoden James B JB Zhuang Zhihao Z Latham John J Trujillo Michael M Holden Hazel M HM Dunaway-Mariano Debra D

Biochemistry 20120820 35

The hotdog-fold enzyme 4-hydroxybenzoyl-coenzyme A (4-HB-CoA) thioesterase from Arthrobacter sp. strain AU catalyzes the hydrolysis of 4-HB-CoA to form 4-hydroxybenzoate (4-HB) and coenzyme A (CoA) in the final step of the 4-chlorobenzoate dehalogenation pathway. Guided by the published X-ray structures of the liganded enzyme (Thoden, J. B., Zhuang, Z., Dunaway-Mariano, D., and Holden H. M. (2003) J. Biol. Chem. 278, 43709-43716), a series of site-directed mutants were prepared for testing the r ...[more]

PMID: 22873756

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Project description:The 4-hydroxybenzoyl-CoA (4-HB-CoA) thioesterase from Pseudomonas sp. strain CBS3 catalyzes the final step of the 4-chlorobenzoate degradation pathway, which is the hydrolysis of 4-HB-CoA to coenzyme A (CoA) and 4-hydroxybenzoate (4-HB). In previous work, X-ray structural analysis of the substrate-bound thioesterase provided evidence of the role of an active site Asp17 in nucleophilic catalysis [Thoden, J. B., Holden, H. M., Zhuang, Z., and Dunaway-Mariano, D. (2002) X-ray crystallographic analyses of inhibitor and substrate complexes of wild-type and mutant 4-hydroxybenzoyl-CoA thioesterase. J. Biol. Chem. 277, 27468-27476]. In the study presented here, kinetic techniques were used to test the catalytic mechanism that was suggested by the X-ray structural data. The time course for the multiple-turnover reaction of 50 ?M [(14)C]-4-HB-CoA catalyzed by 10 ?M thioesterase supported a two-step pathway in which the second step is rate-limiting. Steady-state product inhibition studies revealed that binding of CoA (K(is) = 250 ± 70 ?M; K(ii) = 900 ± 300 ?M) and 4-HB (K(is) = 1.2 ± 0.2 mM) is weak, suggesting that product release is not rate-limiting. A substantial D(2)O solvent kinetic isotope effect (3.8) on the steady-state k(cat) value (18 s(-1)) provided evidence that a chemical step involving proton transfer is the rate-limiting step. Taken together, the kinetic results support a two-chemical pathway. The microscopic rate constants governing the formation and consumption of the putative aspartyl 17-(4-hydroxybenzoyl)anhydride intermediate were determined by simulation-based fitting of a kinetic model to time courses for the substrate binding reaction (5.0 ?M 4-HB-CoA and 0.54 ?M thioesterase), single-turnover reaction (5 ?M [(14)C]-4-HB-CoA catalyzed by 50 ?M thioesterase), steady-state reaction (5.2 ?M 4-HB-CoA catalyzed by 0.003 ?M thioesterase), and transient-state multiple-turnover reaction (50 ?M [(14)C]-4-HB-CoA catalyzed by 10 ?M thioesterase). Together with the results obtained from solvent (18)O labeling experiments, the findings are interpreted as evidence of the formation of an aspartyl 17-(4-hydroxybenzoyl)anhydride intermediate that undergoes rate-limiting hydrolytic cleavage at the hydroxybenzoyl carbonyl carbon atom.

Dataset Information

The catalytic mechanism of the hotdog-fold enzyme superfamily 4-hydroxybenzoyl-CoA thioesterase from Arthrobacter sp. strain SU.

Publications

The catalytic mechanism of the hotdog-fold enzyme superfamily 4-hydroxybenzoyl-CoA thioesterase from Arthrobacter sp. strain SU.

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