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Katsuki N, Fukushima R, Doi Y, Masuo S, Arakawa T, Yamada C, Fushinobu S, Takaya N. Protocatechuate hydroxylase is a novel group A flavoprotein monooxygenase with a unique substrate recognition mechanism. J Biol Chem 2024; 300:105508. [PMID: 38029967 PMCID: PMC10770758 DOI: 10.1016/j.jbc.2023.105508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Revised: 11/20/2023] [Accepted: 11/22/2023] [Indexed: 12/01/2023] Open
Abstract
Para-hydroxybenzoate hydroxylase (PHBH) is a group A flavoprotein monooxygenase that hydroxylates p-hydroxybenzoate to protocatechuate (PCA). Despite intensive studies of Pseudomonas aeruginosa p-hydroxybenzoate hydroxylase (PaPobA), the catalytic reactions of extremely diverse putative PHBH isozymes remain unresolved. We analyzed the phylogenetic relationships of known and predicted PHBHs and identified eight divergent clades. Clade F contains a protein that lacks the critical amino acid residues required for PaPobA to generate PHBH activity. Among proteins in this clade, Xylophilus ampelinus PobA (XaPobA) preferred PCA as a substrate and is the first known natural PCA 5-hydroxylase (PCAH). Crystal structures and kinetic properties revealed similar mechanisms of substrate carboxy group recognition between XaPobA and PaPobA. The unique Ile75, Met72, Val199, Trp201, and Phe385 residues of XaPobA form the bottom of a hydrophobic cavity with a shape that complements the 3-and 4-hydroxy groups of PCA and its binding site configuration. An interaction between the δ-sulfur atom of Met210 and the aromatic ring of PCA is likely to stabilize XaPobA-PCA complexes. The 4-hydroxy group of PCA forms a hydrogen bond with the main chain carbonyl of Thr294. These modes of binding constitute a novel substrate recognition mechanism that PaPobA lacks. This mechanism characterizes XaPobA and sheds light on the diversity of catalytic mechanisms of PobA-type PHBHs and group A flavoprotein monooxygenases.
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Affiliation(s)
- Nozomi Katsuki
- Faculty of Life and Environmental Sciences, Microbiology Research Center for Sustainability, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Riku Fukushima
- Department of Biotechnology, The University of Tokyo, Tokyo, Japan
| | - Yuki Doi
- Faculty of Life and Environmental Sciences, Microbiology Research Center for Sustainability, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Shunsuke Masuo
- Faculty of Life and Environmental Sciences, Microbiology Research Center for Sustainability, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Takatoshi Arakawa
- Faculty of Pharmaceutical Sciences, Tokyo University of Science, Noda, Chiba, Japan
| | - Chihaya Yamada
- School of Agriculture, Meiji University, Kawasaki, Kanagawa, Japan
| | - Shinya Fushinobu
- Department of Biotechnology, The University of Tokyo, Tokyo, Japan; Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, Tokyo, Japan.
| | - Naoki Takaya
- Faculty of Life and Environmental Sciences, Microbiology Research Center for Sustainability, University of Tsukuba, Tsukuba, Ibaraki, Japan.
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2
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Nonaka K, Osamura T, Takahashi F. A 4-hydroxybenzoate 3-hydroxylase mutant enables 4-amino-3-hydroxybenzoic acid production from glucose in Corynebacterium glutamicum. Microb Cell Fact 2023; 22:168. [PMID: 37644492 PMCID: PMC10466732 DOI: 10.1186/s12934-023-02179-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 08/14/2023] [Indexed: 08/31/2023] Open
Abstract
BACKGROUND Microbial production of aromatic chemicals is an attractive method for obtaining high-performance materials from biomass resources. A non-proteinogenic amino acid, 4-amino-3-hydroxybenzoic acid (4,3-AHBA), is expected to be a precursor of highly functional polybenzoxazole polymers; however, methods for its microbial production have not been reported. In this study, we attempted to produce 4,3-AHBA from glucose by introducing 3-hydroxylation of 4-aminobenzoic acid (4-ABA) into the metabolic pathway of an industrially relevant bacterium, Corynebacterium glutamicum. RESULTS Six different 4-hydroxybenzoate 3-hydroxylases (PHBHs) were heterologously expressed in C. glutamicum strains, which were then screened for the production of 4,3-AHBA by culturing with glucose as a carbon source. The highest concentration of 4,3-AHBA was detected in the strain expressing PHBH from Caulobacter vibrioides (CvPHBH). A combination of site-directed mutagenesis in the active site and random mutagenesis via laccase-mediated colorimetric assay allowed us to obtain CvPHBH mutants that enhanced 4,3-AHBA productivity under deep-well plate culture conditions. The recombinant C. glutamicum strain expressing CvPHBHM106A/T294S and having an enhanced 4-ABA biosynthetic pathway produced 13.5 g/L (88 mM) 4,3-AHBA and 0.059 g/L (0.43 mM) precursor 4-ABA in fed-batch culture using a nutrient-rich medium. The culture of this strain in the chemically defined CGXII medium yielded 9.8 C-mol% of 4,3-AHBA from glucose, corresponding to 12.8% of the theoretical maximum yield (76.8 C-mol%) calculated using a genome-scale metabolic model of C. glutamicum. CONCLUSIONS Identification of PHBH mutants that could efficiently catalyze the 3-hydroxylation of 4-ABA in C. glutamicum allowed us to construct an artificial biosynthetic pathway capable of producing 4,3-AHBA on a gram-scale using glucose as the carbon source. These findings will contribute to a better understanding of enzyme-catalyzed regioselective hydroxylation of aromatic chemicals and to the diversification of biomass-derived precursors for high-performance materials.
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Affiliation(s)
- Kyoshiro Nonaka
- Biological Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama, 640-8580, Japan.
| | - Tatsuya Osamura
- Biological Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama, 640-8580, Japan
| | - Fumikazu Takahashi
- Biological Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama, 640-8580, Japan
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3
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Beaupre BA, Reabe KR, Roman JV, Moran GR. Hydrogen movements in the oxidative half-reaction of kynurenine 3-monooxygenase from Pseudomonas fluorescens reveal the mechanism of hydroxylation. Arch Biochem Biophys 2020; 690:108474. [PMID: 32687799 DOI: 10.1016/j.abb.2020.108474] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Revised: 06/08/2020] [Accepted: 06/17/2020] [Indexed: 11/30/2022]
Abstract
Kynurenine 3-monoxygenase (KMO) catalyzes the conversion of l-kynurenine (L-Kyn) to 3-hydroxykynurenine (3-OHKyn) in the pathway for tryptophan catabolism. We have investigated the effects of pH and deuterium substitution on the oxidative half-reaction of KMO from P. fluorescens (PfKMO). The three phases observed during the oxidative half reaction are formation of the hydroperoxyflavin, hydroxylation and product release. The measured rate constants for these phases proved largely unchanging with pH, suggesting that the KMO active site is insulated from exchange with solvent during catalysis. A solvent inventory study indicated that a solvent isotope effect of 2-3 is observed for the hydroxylation phase and that two or more protons are in flight during this step. An inverse isotope effect of 0.84 ± 0.01 on the rate constant for the hydroxylation step with ring perdeutero-L-Kyn as a substrate indicates a shift from sp2 to sp3 hybridization in the transition state leading to the formation of a non-aromatic intermediate. The pH dependence of transient state data collected for the substrate analog meta-nitrobenzoylalanine indicate that groups proximal to the hydroperoxyflavin are titrated in the range pH 5-8.5 and can be described by a pKa of 8.8. That higher pH values do not slow the rate of hydroxylation precludes that the pKa measured pertains to the proton of the hydroperoxflavin. Together, these observations indicate that the C4a-hydroperoxyflavin has a pKa ≫ 8.5, that a non-aromatic species is the immediate product of hydroxylation and that at least two solvent derived protons are in-flight during oxygen insertion to the substrate aromatic ring. A unifying mechanistic proposal for these observations is proposed.
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Affiliation(s)
- Brett A Beaupre
- Department of Chemistry and Biochemistry, 1068 W Sheridan Rd, Loyola University Chicago, Chicago, IL, 60660, USA
| | - Karen R Reabe
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, 3210 N. Cramer Street, Milwaukee, WI, 53211-3029, USA
| | - Joseph V Roman
- Department of Chemistry and Biochemistry, 1068 W Sheridan Rd, Loyola University Chicago, Chicago, IL, 60660, USA
| | - Graham R Moran
- Department of Chemistry and Biochemistry, 1068 W Sheridan Rd, Loyola University Chicago, Chicago, IL, 60660, USA.
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4
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Rudolph J, Erbse AH, Behlen LS, Copley SD. A radical intermediate in the conversion of pentachlorophenol to tetrachlorohydroquinone by Sphingobium chlorophenolicum. Biochemistry 2014; 53:6539-49. [PMID: 25238136 PMCID: PMC4204890 DOI: 10.1021/bi5010427] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Pentachlorophenol
(PCP) hydroxylase, the first enzyme in the pathway
for degradation of PCP in Sphingobium chlorophenolicum, is an unusually slow flavin-dependent monooxygenase (kcat = 0.02 s–1) that converts PCP to
a highly reactive product, tetrachlorobenzoquinone (TCBQ). Using stopped-flow
spectroscopy, we have shown that the steps up to and including formation
of TCBQ are rapid (5–30 s–1). Before products
can be released from the active site, the strongly oxidizing TCBQ
abstracts an electron from a donor at the active site, possibly a
cysteine residue, resulting in an off-pathway diradical state that
only slowly reverts to an intermediate capable of completing the catalytic
cycle. TCBQ reductase, the second enzyme in the PCP degradation pathway,
rescues this nonproductive complex via two fast sequential one-electron
transfers. These studies demonstrate how adoption of an ancestral
catalytic strategy for conversion of a substrate with different steric
and electronic properties can lead to subtle yet (literally) radical
changes in enzymatic reaction mechanisms.
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Affiliation(s)
- Johannes Rudolph
- Department of Molecular, Cellular and Developmental Biology and the Cooperative Institute for Research in Environmental Sciences, and ‡Department of Chemistry and Biochemistry, University of Colorado Boulder , Boulder, Colorado 80309, United States
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5
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Suemori A. Conserved and non-conserved residues and their role in the structure and function of p-hydroxybenzoate hydroxylase. Protein Eng Des Sel 2013; 26:479-88. [PMID: 23766373 DOI: 10.1093/protein/gzt026] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In order to elucidate the molecular mechanism of the catalytic reaction and enzyme conformation, we substituted 53 conserved residues identified by aligning 92 p-hydroxybenzoate hydroxylase sequences and 19 non-conserved residues selected from crystallographic studies of Pseudomonas fluorescens NBRC14160 p-hydroxybenzoate hydroxylase with 19 other naturally occurring amino acids, yielding a database of 619 active single mutants. The database contained 365 and 254 active single mutants for 44/53 conserved residues and 19 non-conserved residues, respectively; the data included main activity, sub-activity for NADPH and NADPH reaction specificity. Active mutations were not observed for the G14, Q102, G160, E198, R220, R246, N300, F342 and G387 conserved residues, and only one active mutant was obtained at the G9, G11, G187, D286, Y201, R214 and G295 conserved residues and the S13, E32 and R42 non-conserved residues. Only seven active mutants with higher activity than the wild-type enzyme were observed at conserved residues, and only two were observed at non-conserved residues. The 365 mutants at conserved residues included 64 active mutants with higher NADPH reaction specificity than the wild-type enzyme, and some Y181X single mutants exhibited considerable changes in NADPH reaction specificity. A Y181X/L268G double-mutant database was constructed to computationally analyze the effects of these substitutions on structural conformation and function. These results indicated that some conserved or non-conserved residues are important for structural stability or enzyme function.
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Affiliation(s)
- Akio Suemori
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology-AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
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6
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Form follows function: structural and catalytic variation in the class a flavoprotein monooxygenases. Int J Mol Sci 2012; 13:15601-39. [PMID: 23443084 PMCID: PMC3546652 DOI: 10.3390/ijms131215601] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 11/08/2012] [Accepted: 11/09/2012] [Indexed: 12/02/2022] Open
Abstract
Flavoprotein monooxygenases (FPMOs) exhibit an array of mechanistic solutions to a common chemical objective; the monooxygenation of a target substrate. Each FPMO efficiently couples reduction of a flavin cofactor by NAD(P)H to oxygenation of the target substrate via a (hydro)peroxyflavin intermediate. This purpose of this review is to describe in detail the Class A flavoprotein hydroxylases (FPMO) in the context of the other FPMO classes (B–F). Both one and two component FPMOs are found in nature. Two-component enzymes require, in addition to the monooxygenase, the involvement of a reductase that first catalyzes the reduction of the flavin by NAD(P)H. The Class A and B FPMOs are single-component and manage to orchestrate the same net reaction within a single peptide. The Class A enzymes have, by some considerable margin, the most complete research record. These enzymes use choreographed movements of the flavin ring that facilitate access of the organic substrates to the active site, provide a means for interaction of NADPH with the flavin, offer a mechanism to sequester the dioxygen reduction chemistry from solvent and a means to release the product. The majority of the discrete catalytic events of the catalytic cycle can be observed directly in exquisite detail using spectrophotometric kinetic methods and many of the key mechanistic conclusions are further supported by structural data. This review attempts to compile each of the key observations made for both paradigm and newly discovered examples of Class A FPMOs into a complete catalytic description of one enzymatic turnover.
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7
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Meneely KM, Barr EW, Bollinger JM, Lamb AL. Kinetic mechanism of ornithine hydroxylase (PvdA) from Pseudomonas aeruginosa: substrate triggering of O2 addition but not flavin reduction. Biochemistry 2009; 48:4371-6. [PMID: 19368334 DOI: 10.1021/bi900442z] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PvdA catalyzes the hydroxylation of the side chain primary amine of ornithine in the initial step of the biosynthesis of the Pseudomonas aeruginosa siderophore pyoverdin. The reaction requires FAD, NADPH, and O(2). PvdA uses the same cosubstrates as several flavin-dependent hydroxylases that differ one from another in the kinetic mechanisms of their oxidative and reductive half-reactions. Therefore, the mechanism of PvdA was determined by absorption stopped-flow experiments. By contrast to some flavin-dependent hydroxylases (notably, p-hydroxybenzoate hydroxylase), binding of the hydroxylation target is not required to trigger reduction of the flavin by NADPH: the reductive half-reaction is equally facile in the presence and absence of ornithine. Reaction of O(2) with FADH(2) in the oxidative half-reaction is accelerated by ornithine 80-fold, providing a mechanism by which PvdA can ensure coupling of NADPH and ornithine oxidation. In the presence of ornithine, the expected C(4a)-hydroperoxyflavin intermediate with 390 nm absorption accumulates and decays to the C(4a)-hydroxyflavin in a kinetically competent fashion. The slower oxidative half-reaction that occurs in the absence of ornithine involves accumulation of an oxygenated flavin species and two subsequent states that are tentatively assigned as C(4a)-peroxy- and C(4a)-hydroperoxyflavin intermediates and the oxidized flavin. The enzyme generates stoichiometric hydrogen peroxide in lieu of hydroxyornithine. The data suggest that PvdA employs a kinetic mechanism that is a hybrid of those previously documented for other flavin-dependent hydroxylases.
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Affiliation(s)
- Kathleen M Meneely
- Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, Kansas 66045, USA
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8
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Crozier-Reabe KR, Phillips RS, Moran GR. Kynurenine 3-monooxygenase from Pseudomonas fluorescens: substrate-like inhibitors both stimulate flavin reduction and stabilize the flavin-peroxo intermediate yet result in the production of hydrogen peroxide. Biochemistry 2009; 47:12420-33. [PMID: 18954092 DOI: 10.1021/bi8010434] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Kynurenine 3-monooxygenase (KMO) is a flavin-dependent hydroxylase that catalyzes the conversion of l-kynurenine (l-Kyn) to 3-hydroxykynurenine (3OHKyn) in the pathway for tryptophan catabolism. KMO inhibition has been widely suggested as an early treatment for stroke and other neurological disorders that involve ischemia. We have investigated the reductive and the oxidative half-reactions of a stable form of KMO from Pseudomonas fluorescens (KMO). The binding of l-Kyn by the enzyme is relatively slow and involves at least two reversible steps. The rate constant for reduction of the flavin cofactor by NADPH increases by a factor of approximately 2.5 x 10(3) when l-Kyn is bound. The rate of reduction of the KMO.l-Kyn complex is 160 s(-1), and the K(d) for the NADPH complex is 200 microM with charge-transfer absorption bands for the KMO(RED).l-Kyn.NADP(+) complex accumulating after reduction. The reduction potential of KMO is -188 mV and is unresponsive to the addition of l-Kyn or other inhibitory ligands. KMO inhibitors whose structures are reminiscent of l-Kyn such as m-nitrobenzoylalanine and benzoylalanine also stimulate reduction of flavin by NADPH and, in the presence of dioxygen, result in the stoichiometric liberation of hydrogen peroxide, diminishing the perceived therapeutic potential of inhibitors of this type. In the presence of the native substrate, the oxidative half-reaction exhibits triphasic absorbance data. A spectrum consistent with that of a peroxyflavin species accumulates and then decays to yield the oxidized enzyme. This species then undergoes minor spectral changes that, based on flavin difference spectra defined in the presence of 3OHKyn, can be correlated with product release. The oxidative half-reaction observed in the presence of saturating benzoylalanine or m-nitrobenzoylalanine also shows the accumulation of a peroxyflavin species that then decays to yield hydrogen peroxide without hydroxylation.
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Affiliation(s)
- Karen R Crozier-Reabe
- Department of Chemistry and Biochemistry, University of Wisconsin, 3210 North Cramer Street, Milwaukee, Wisconsin 53211-3029, USA
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9
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Time-resolved fluorescence analysis of the mobile flavin cofactor in p-hydroxybenzoate hydroxylase. J CHEM SCI 2007. [DOI: 10.1007/s12039-007-0019-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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10
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Ballou DP, Entsch B, Cole LJ. Dynamics involved in catalysis by single-component and two-component flavin-dependent aromatic hydroxylases. Biochem Biophys Res Commun 2005; 338:590-8. [PMID: 16236251 DOI: 10.1016/j.bbrc.2005.09.081] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Accepted: 09/13/2005] [Indexed: 10/25/2022]
Abstract
Flavoprotein monooxygenases are involved in a wide variety of biological processes including drug detoxification, biodegradation of aromatic compounds in the environment, biosynthesis of antibiotics and siderophores, and many others. The reactions use NAD(P)H and O2 as co-substrates and insert one atom of oxygen into the substrate. The flavin-dependent monooxygenases utilize a general cycle in which NAD(P)H reduces the flavin, and the reduced flavin reacts with O2 to form a C4a-(hydro)peroxyflavin intermediate, which is the oxygenating agent. This complicated catalytic process has diverse requirements that are difficult to be satisfied by a single site. Two general strategies have evolved to satisfy these requirements. para-Hydroxybenzoate hydroxylase, the paradigm for the single-component flavoprotein monooxygenases, is one of the most thoroughly studied of all enzymes. This enzyme undergoes significant protein and flavin dynamics during catalysis. There is an open conformation that gives access of substrate and product to solvent, and a closed or in conformation for the reaction with oxygen and the hydroxylation to occur. This closed form prevents solvent from destabilizing the hydroperoxyflavin intermediate. Finally, there is an out conformation achieved by movement of the isoalloxazine toward the solvent, which exposes its N5 for hydride delivery from NAD(P)H. The protein coordinates these dynamic events during catalysis. The second strategy uses a reductase to catalyze the reduction of the flavin and an oxygenase that uses the reduced flavin as a substrate to react with oxygen and hydroxylate the organic substrate. These two-component systems must be able to transfer reduced flavin from the reductase to the oxygenase and stabilize a C4a-peroxyflavin until a substrate binds to be hydroxylated, all before flavin oxidation and release of H2O2. Again, protein dynamics are important for catalytic success.
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Affiliation(s)
- David P Ballou
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0606, USA.
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11
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Young DM, D'Argenio DA, Jen M, Parke D, Nicholas Ornston L. Gunsalus and Stanier set the stage for selection of cold-sensitive mutants apparently impaired in movement of FAD within 4-hydroxybenzoate hydroxylase. Biochem Biophys Res Commun 2004; 312:153-60. [PMID: 14630034 DOI: 10.1016/j.bbrc.2003.09.240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- David M Young
- Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., D1-219, Boston, MA 02115, USA
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12
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Abe I, Kashiwagi K, Noguchi H. Antioxidative galloyl esters as enzyme inhibitors of p-hydroxybenzoate hydroxylase. FEBS Lett 2000; 483:131-4. [PMID: 11042267 DOI: 10.1016/s0014-5793(00)02100-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Gallic acid and its esters were evaluated as enzyme inhibitors of recombinant p-hydroxybenzoate hydroxylase (PHBH), a NADPH-dependent flavin monooxygenase from Pseudomonas aeruginosa. n-Dodecyl gallate (DG) (IC(50)=16 microM) and (-)-epigallocatechin-3-O-gallate (EGCG) (IC(50)=16 microM), a major component of green tea polyphenols, showed the most potent inhibition, while product-like gallic acid did not inhibit the enzyme significantly (IC(50)>250 microM). Inhibition kinetics revealed that both DG and EGCG inhibited PHBH in a non-competitive manner (K(I)=18.1 and 14.0 microM, respectively). The enzyme inhibition was caused by specific binding of the antioxidative gallate to the enzyme, and by scavenging reactive oxygen species required for the monooxygenase reaction. Molecular modeling predicted that EGCG binds to the enzyme in the proximity of the FAD binding site via formation of three hydrogen bonds.
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Affiliation(s)
- I Abe
- School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan.
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