Crystallization of a Unique Flavonol 3-O Glucosyltransferase found in Grapefruit

Authors' Affiliations

Aaron Birchfield, Cecilia McIntosh East Tennessee State University, Department of Biological Sciences, Johnson City, TN 37601, USA

Location

Culp Room 303

Start Date

4-6-2022 9:00 AM

End Date

4-6-2022 10:00 AM

Faculty Sponsor’s Department

Biological Sciences

Name of Project's Faculty Sponsor

Cecilia McIntosh

Classification of First Author

Graduate Student-Doctoral

Competition Type

Competitive

Type

Oral Presentation

Project's Category

Enzyme Catalysis

Abstract or Artist's Statement

Flavonoids are a specialized group of compounds produced by plants that give them greater adaptability to their environment and ultimately enhance their ability to survive. In plants, one function of flavonoids is to attract pollinators by their various flavor and scent profiles. They also protect the photosynthetic machinery from photo-oxidation. In humans, flavonoids have been shown to act as antioxidants, exhibit antimicrobial activity, and have shown potential as cancer treatments. In nature, flavonoids are most often found coupled with a sugar group (glucose, rhamnose, and others) which imparts stability and increases bioactivity. The process of adding a sugar (glycosylation) is catalyzed by a class of enzymes called glycosyltransferases (GT). One such enzyme found in grapefruit only glucosylates the flavonol class of flavonoids at the 3-OH position and is of interest due to its unique substrate and regio-specificity. Called Cp3GT (Citrus paradisi flavonol 3-O glucosyltransferase), this enzyme is similar in structure to other plant GT’s yet differs in the flavonoids it can glucosylate and where the glucose can be added. To date, the literature has not reported a structural mechanism for a flavonol specific 3-O glucosyltransferase’s unique catalytic activity. High-resolution structural imagery of enzymes, elucidated using X-ray crystallography, can be used to direct custom enzyme development to produce bioavailable natural products. Furthermore, structural research on enzymes with high specificity strengthens enzyme-ligand docking simulations, which are commonly used to test the binding affinity of potential pharmaceuticals. This research hypothesizes Cp3GT has structural features that confer its unique substrate and regiospecificity that are not revealed by homology modeling. This hypothesis will be tested using x-ray crystallography of purified Cp3GT protein bound to its preferred flavonol substrates. The gene for Cp3GT was transformed into Pichia pastoris and was recombinantly expressed using methanol induction. Cp3GT was purified to 80% purity using cobalt metal affinity chromatography. Cp3GT was subjected to additional purification measures using anion exchange chromatography with the goal of increasing purity to ≥95% for crystallization experiments. Purity analysis was conducted using SDS-PAGE (Coomassie/silver stain, western blot) and UV-Vis spectrophotometry. While initial results are promising, additional purification steps may be needed to achieve the purity necessary for crystallization.

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Apr 6th, 9:00 AM Apr 6th, 10:00 AM

Crystallization of a Unique Flavonol 3-O Glucosyltransferase found in Grapefruit

Culp Room 303

Flavonoids are a specialized group of compounds produced by plants that give them greater adaptability to their environment and ultimately enhance their ability to survive. In plants, one function of flavonoids is to attract pollinators by their various flavor and scent profiles. They also protect the photosynthetic machinery from photo-oxidation. In humans, flavonoids have been shown to act as antioxidants, exhibit antimicrobial activity, and have shown potential as cancer treatments. In nature, flavonoids are most often found coupled with a sugar group (glucose, rhamnose, and others) which imparts stability and increases bioactivity. The process of adding a sugar (glycosylation) is catalyzed by a class of enzymes called glycosyltransferases (GT). One such enzyme found in grapefruit only glucosylates the flavonol class of flavonoids at the 3-OH position and is of interest due to its unique substrate and regio-specificity. Called Cp3GT (Citrus paradisi flavonol 3-O glucosyltransferase), this enzyme is similar in structure to other plant GT’s yet differs in the flavonoids it can glucosylate and where the glucose can be added. To date, the literature has not reported a structural mechanism for a flavonol specific 3-O glucosyltransferase’s unique catalytic activity. High-resolution structural imagery of enzymes, elucidated using X-ray crystallography, can be used to direct custom enzyme development to produce bioavailable natural products. Furthermore, structural research on enzymes with high specificity strengthens enzyme-ligand docking simulations, which are commonly used to test the binding affinity of potential pharmaceuticals. This research hypothesizes Cp3GT has structural features that confer its unique substrate and regiospecificity that are not revealed by homology modeling. This hypothesis will be tested using x-ray crystallography of purified Cp3GT protein bound to its preferred flavonol substrates. The gene for Cp3GT was transformed into Pichia pastoris and was recombinantly expressed using methanol induction. Cp3GT was purified to 80% purity using cobalt metal affinity chromatography. Cp3GT was subjected to additional purification measures using anion exchange chromatography with the goal of increasing purity to ≥95% for crystallization experiments. Purity analysis was conducted using SDS-PAGE (Coomassie/silver stain, western blot) and UV-Vis spectrophotometry. While initial results are promising, additional purification steps may be needed to achieve the purity necessary for crystallization.