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Properties of p-hydroxybenzoate hydroxylase when stabilized in its open conformation.
Biochemistry. 2005 Nov 15; 44(45):14807-17.B

Abstract

p-Hydroxybenzoate hydroxylase is extensively studied as a model for single-component flavoprotein monooxygenases. It catalyzes a reaction in two parts: (1) reduction of the FAD in the enzyme by NADPH in response to binding of p-hydroxybenzoate to the enzyme and (2) oxidation of reduced FAD with oxygen in an environment free from solvent to form a hydroperoxide, which then reacts with p-hydroxybenzoate to form an oxygenated product. These different reactions are coordinated through conformational rearrangements of the protein and the isoalloxazine ring during catalysis. Until recently, it has not been clear how p-hydroxybenzoate gains access to the buried active site. In 2002, a structure of a mutant form of the enzyme without substrate was published that showed an open conformation with solvent access to the active site [Wang, J., Ortiz-Maldonado, M., Entsch, B., Massey, V., Ballou, D., and Gatti, D. L. (2002) Proc. Natl. Acad. Sci. U.S.A. 99, 608-613]. The wild-type enzyme does not form high-resolution crystals without substrate. We hypothesized that the wild-type enzyme without substrate also forms an open conformation for binding p-hydroxybenzoate, but only transiently. To test this idea, we have studied the properties of two different mutant forms of the enzyme that are stabilized in the open conformation. These mutant enzymes bind p-hydroxybenzoate very fast, but with very low affinity, as expected from the open structure. The mutant enzymes are extremely inactive, but are capable of slowly forming small amounts of product by the normal catalytic pathway. The lack of activity results from the failure of the mutants to readily form the out conformation required for flavin reduction by NADPH. The mutants form a large fraction of an abnormal conformation of the reduced enzyme with p-hydroxybenzoate bound. This conformation of the enzyme is unreactive with oxygen. We conclude that transient formation of this open conformation is the mechanism for sequestering p-hydroxybenzoate to initiate catalysis. This overall study emphasizes the role that protein dynamics can play in enzymatic catalysis.

Authors+Show Affiliations

Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

16274228

Citation

Cole, Lindsay J., et al. "Properties of P-hydroxybenzoate Hydroxylase when Stabilized in Its Open Conformation." Biochemistry, vol. 44, no. 45, 2005, pp. 14807-17.
Cole LJ, Entsch B, Ortiz-Maldonado M, et al. Properties of p-hydroxybenzoate hydroxylase when stabilized in its open conformation. Biochemistry. 2005;44(45):14807-17.
Cole, L. J., Entsch, B., Ortiz-Maldonado, M., & Ballou, D. P. (2005). Properties of p-hydroxybenzoate hydroxylase when stabilized in its open conformation. Biochemistry, 44(45), 14807-17.
Cole LJ, et al. Properties of P-hydroxybenzoate Hydroxylase when Stabilized in Its Open Conformation. Biochemistry. 2005 Nov 15;44(45):14807-17. PubMed PMID: 16274228.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Properties of p-hydroxybenzoate hydroxylase when stabilized in its open conformation. AU - Cole,Lindsay J, AU - Entsch,Barrie, AU - Ortiz-Maldonado,Mariliz, AU - Ballou,David P, PY - 2005/11/9/pubmed PY - 2006/1/5/medline PY - 2005/11/9/entrez SP - 14807 EP - 17 JF - Biochemistry JO - Biochemistry VL - 44 IS - 45 N2 - p-Hydroxybenzoate hydroxylase is extensively studied as a model for single-component flavoprotein monooxygenases. It catalyzes a reaction in two parts: (1) reduction of the FAD in the enzyme by NADPH in response to binding of p-hydroxybenzoate to the enzyme and (2) oxidation of reduced FAD with oxygen in an environment free from solvent to form a hydroperoxide, which then reacts with p-hydroxybenzoate to form an oxygenated product. These different reactions are coordinated through conformational rearrangements of the protein and the isoalloxazine ring during catalysis. Until recently, it has not been clear how p-hydroxybenzoate gains access to the buried active site. In 2002, a structure of a mutant form of the enzyme without substrate was published that showed an open conformation with solvent access to the active site [Wang, J., Ortiz-Maldonado, M., Entsch, B., Massey, V., Ballou, D., and Gatti, D. L. (2002) Proc. Natl. Acad. Sci. U.S.A. 99, 608-613]. The wild-type enzyme does not form high-resolution crystals without substrate. We hypothesized that the wild-type enzyme without substrate also forms an open conformation for binding p-hydroxybenzoate, but only transiently. To test this idea, we have studied the properties of two different mutant forms of the enzyme that are stabilized in the open conformation. These mutant enzymes bind p-hydroxybenzoate very fast, but with very low affinity, as expected from the open structure. The mutant enzymes are extremely inactive, but are capable of slowly forming small amounts of product by the normal catalytic pathway. The lack of activity results from the failure of the mutants to readily form the out conformation required for flavin reduction by NADPH. The mutants form a large fraction of an abnormal conformation of the reduced enzyme with p-hydroxybenzoate bound. This conformation of the enzyme is unreactive with oxygen. We conclude that transient formation of this open conformation is the mechanism for sequestering p-hydroxybenzoate to initiate catalysis. This overall study emphasizes the role that protein dynamics can play in enzymatic catalysis. SN - 0006-2960 UR - https://www.unboundmedicine.com/medline/citation/16274228/Properties_of_p_hydroxybenzoate_hydroxylase_when_stabilized_in_its_open_conformation_ L2 - https://doi.org/10.1021/bi0512142 DB - PRIME DP - Unbound Medicine ER -