Biochemical properties and cyclodextrin production profiles of isoforms of cyclodextrin glycosyltransferase

Fisetin glycosides synthesized by cyclodextrin glycosyltransferase from Paenibacillus sp. RB01: characterization, molecular docking, and antioxidant activity

Fisetin is a flavonoid that exhibits high antioxidant activity and is widely employed in the pharmacological industries. However, the application of fisetin is limited due to its low water solubility. In this study, glycoside derivatives of fisetin were synthesized by an enzymatic reaction using cyclodextrin glycosyltransferase (CGTase) from Paenibacillus sp. RB01 in order to improve the water solubility of fisetin. Under optimal conditions, CGTase was able to convert more than 400 mg/L of fisetin to its glycoside derivatives, which is significantly higher than the previous biosynthesis using engineered E. coli. Product characterization by HPLC and LC-MS/MS revealed that the transglycosylated products consisted of at least five fisetin glycoside derivatives, including fisetin mono-, di- and triglucosides, as well as their isomers. Enzymatic analysis by glucoamylase and α-glucosidase showed that these fisetin glycosides were formed by α-1,4-glycosidic linkages. Molecular docking demonstrated that there are two possible binding modes of fisetin in the enzyme active site containing CGTase-glysosyl intermediate, in which O7 and O4' atoms of fisetin positioned close to the C1 of glycoside donor, corresponding to the isomers of the obtained fisetin monoglucosides. In addition, the water solubility and the antioxidant activity of the fisetin monoglucosides were tested. It was found that their water solubility was increased at least 800 times when compared to that of their parent molecule while still maintaining the antioxidant activity. This study revealed the potential application of CGTase to improve the solubility of flavonoids.

Identification, cloning and expression analysis of an alpha-CGTase produced by stain Y112

Cyclodextrin glycosyltransferase (CGTase) is an enzyme able to convert starch and other substrates into cyclodextrins (CDs). A marine strain Y112 producing α-CGTase was identified as Bacillus agaradhaerens Y112 by physiological and biochemical characterization, and 16S rDNA analysis. The gene coding for α-CGTase was cloned, sequenced and expressed in Escherichia coli BL21 (DE3) cells. Recombinant α-CGTase was purified in one-step chromatographic separation and its purity evaluated by SDS-PAGE, showing the presence of one band with a molecular mass of about 92 kDa. Additionally, enzymatic capability was analyzed by measuring the starch conversion, and resulted in about 45% of CDs obtained after 6 h of cyclodextrin reaction. Of these CDs, mainly α-CD was produced (70% of the total CDs yield), suggesting the potential of this CGTase for industrial applications.