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Structural basis for certain naturally occurring bioflavonoids to function as reducing co-substrates of cyclooxygenase I and II.

Wang P, Bai HW, Zhu BT - PLoS ONE (2010)

Bottom Line: The docking results were verified by biochemical analysis, which reveals that when the cyclooxygenase activity of COXs is inhibited by covalent modification, myricetin can still stimulate the conversion of PGG(2) to PGE(2), a reaction selectively catalyzed by the peroxidase activity.Using the site-directed mutagenesis analysis, we confirmed that Q189 at the peroxidase site of COX II is essential for bioflavonoids to bind and re-activate its catalytic activity.These findings provide the structural basis for bioflavonoids to function as high-affinity reducing co-substrates of COXs through binding to the peroxidase active site, facilitating electron transfer and enzyme re-activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Toxicology and Therapeutics, School of Medicine, University of Kansas Medical Center, Kansas City, Kansas, United States of America.

ABSTRACT

Background: Recent studies showed that some of the dietary bioflavonoids can strongly stimulate the catalytic activity of cyclooxygenase (COX) I and II in vitro and in vivo, presumably by facilitating enzyme re-activation. In this study, we sought to understand the structural basis of COX activation by these dietary compounds.

Methodology/principal findings: A combination of molecular modeling studies, biochemical analysis and site-directed mutagenesis assay was used as research tools. Three-dimensional quantitative structure-activity relationship analysis (QSAR/CoMFA) predicted that the ability of bioflavonoids to activate COX I and II depends heavily on their B-ring structure, a moiety known to be associated with strong antioxidant ability. Using the homology modeling and docking approaches, we identified the peroxidase active site of COX I and II as the binding site for bioflavonoids. Upon binding to this site, bioflavonoid can directly interact with hematin of the COX enzyme and facilitate the electron transfer from bioflavonoid to hematin. The docking results were verified by biochemical analysis, which reveals that when the cyclooxygenase activity of COXs is inhibited by covalent modification, myricetin can still stimulate the conversion of PGG(2) to PGE(2), a reaction selectively catalyzed by the peroxidase activity. Using the site-directed mutagenesis analysis, we confirmed that Q189 at the peroxidase site of COX II is essential for bioflavonoids to bind and re-activate its catalytic activity.

Conclusions/significance: These findings provide the structural basis for bioflavonoids to function as high-affinity reducing co-substrates of COXs through binding to the peroxidase active site, facilitating electron transfer and enzyme re-activation.

Show MeSH
Chemical structures of the bioflavonoids used in this study.The structure of flavone is enlarged to show the numbering of different carbon positions.
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pone-0012316-g001: Chemical structures of the bioflavonoids used in this study.The structure of flavone is enlarged to show the numbering of different carbon positions.

Mentions: To probe the structural determinants of various bioflavonoids for activating COX I and II, we developed the 3-D QSAR/CoMFA models by using the experimental data obtained from 9 representative bioflavonoids (myricetin, quercetin, fisetin, morin, baicalein, chrysin, apigenin, kaempferol and naringenin) and flavone. These compounds were selected from our recent study [15], and they all share a highly-similar core structure (structures shown in Figure 1). In the QSAR/CoMFA analysis, the experimental values are the COX I- or COX II-mediated production of PGE2 (a major PG formed from AA) in vitro in the presence or absence of a dietary compound [15]. The relevant statistical parameters (PC, q2, r2, SEE, and F) for the CoMFA models of COX I and II are listed in Figure 2. The contributions from the steric and electrostatic fields were 42.5% and 57.5%, respectively, for the COX I CoMFA model, and 56.7% and 43.3%, respectively, for the COX II CoMFA model. There is a high degree of correlation between the experimentally-determined values and the predicted values (Figure 2), with r2 of 0.968 and 0.985, respectively, for COX I and II. In addition, the q2 values are 0.721 and 0.903, respectively. Since the q2 values are far greater than 0.5, it suggests that the 3-D QSAR/CoMFA models developed in this study have a very high predictive ability.


Structural basis for certain naturally occurring bioflavonoids to function as reducing co-substrates of cyclooxygenase I and II.

Wang P, Bai HW, Zhu BT - PLoS ONE (2010)

Chemical structures of the bioflavonoids used in this study.The structure of flavone is enlarged to show the numbering of different carbon positions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2925883&req=5

pone-0012316-g001: Chemical structures of the bioflavonoids used in this study.The structure of flavone is enlarged to show the numbering of different carbon positions.
Mentions: To probe the structural determinants of various bioflavonoids for activating COX I and II, we developed the 3-D QSAR/CoMFA models by using the experimental data obtained from 9 representative bioflavonoids (myricetin, quercetin, fisetin, morin, baicalein, chrysin, apigenin, kaempferol and naringenin) and flavone. These compounds were selected from our recent study [15], and they all share a highly-similar core structure (structures shown in Figure 1). In the QSAR/CoMFA analysis, the experimental values are the COX I- or COX II-mediated production of PGE2 (a major PG formed from AA) in vitro in the presence or absence of a dietary compound [15]. The relevant statistical parameters (PC, q2, r2, SEE, and F) for the CoMFA models of COX I and II are listed in Figure 2. The contributions from the steric and electrostatic fields were 42.5% and 57.5%, respectively, for the COX I CoMFA model, and 56.7% and 43.3%, respectively, for the COX II CoMFA model. There is a high degree of correlation between the experimentally-determined values and the predicted values (Figure 2), with r2 of 0.968 and 0.985, respectively, for COX I and II. In addition, the q2 values are 0.721 and 0.903, respectively. Since the q2 values are far greater than 0.5, it suggests that the 3-D QSAR/CoMFA models developed in this study have a very high predictive ability.

Bottom Line: The docking results were verified by biochemical analysis, which reveals that when the cyclooxygenase activity of COXs is inhibited by covalent modification, myricetin can still stimulate the conversion of PGG(2) to PGE(2), a reaction selectively catalyzed by the peroxidase activity.Using the site-directed mutagenesis analysis, we confirmed that Q189 at the peroxidase site of COX II is essential for bioflavonoids to bind and re-activate its catalytic activity.These findings provide the structural basis for bioflavonoids to function as high-affinity reducing co-substrates of COXs through binding to the peroxidase active site, facilitating electron transfer and enzyme re-activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Toxicology and Therapeutics, School of Medicine, University of Kansas Medical Center, Kansas City, Kansas, United States of America.

ABSTRACT

Background: Recent studies showed that some of the dietary bioflavonoids can strongly stimulate the catalytic activity of cyclooxygenase (COX) I and II in vitro and in vivo, presumably by facilitating enzyme re-activation. In this study, we sought to understand the structural basis of COX activation by these dietary compounds.

Methodology/principal findings: A combination of molecular modeling studies, biochemical analysis and site-directed mutagenesis assay was used as research tools. Three-dimensional quantitative structure-activity relationship analysis (QSAR/CoMFA) predicted that the ability of bioflavonoids to activate COX I and II depends heavily on their B-ring structure, a moiety known to be associated with strong antioxidant ability. Using the homology modeling and docking approaches, we identified the peroxidase active site of COX I and II as the binding site for bioflavonoids. Upon binding to this site, bioflavonoid can directly interact with hematin of the COX enzyme and facilitate the electron transfer from bioflavonoid to hematin. The docking results were verified by biochemical analysis, which reveals that when the cyclooxygenase activity of COXs is inhibited by covalent modification, myricetin can still stimulate the conversion of PGG(2) to PGE(2), a reaction selectively catalyzed by the peroxidase activity. Using the site-directed mutagenesis analysis, we confirmed that Q189 at the peroxidase site of COX II is essential for bioflavonoids to bind and re-activate its catalytic activity.

Conclusions/significance: These findings provide the structural basis for bioflavonoids to function as high-affinity reducing co-substrates of COXs through binding to the peroxidase active site, facilitating electron transfer and enzyme re-activation.

Show MeSH