Glucosylation of (±)-Menthol by Uridine-Diphosphate-Sugar Dependent Glucosyltransferases from Plants

Abstract

Menthol is a cyclic monoterpene alcohol of the essential oils of plants of the genus Mentha, which is in demand by various industries due to its diverse sensorial and physiological properties. However, its poor water solubility and its toxic effect limit possible applications. Glycosylation offers a solution as the binding of a sugar residue to small molecules increases their water solubility and stability, renders aroma components odorless and modifies bioactivity. In order to identify plant enzymes that catalyze this reaction, a glycosyltransferase library containing 57 uridine diphosphate sugar-dependent enzymes (UGTs) was screened with (±)-menthol. The identity of the products was confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy. Five enzymes were able to form (±)-menthyl-β-d-glucopyranoside in whole-cell biotransformations: UGT93Y1, UGT93Y2, UGT85K11, UGT72B27 and UGT73B24. In vitro enzyme activity assays revealed highest catalytic activity for UGT93Y1 (7.6 nkat/mg) from Camellia sinensis towards menthol and its isomeric forms. Although UGT93Y2 shares 70% sequence identity with UGT93Y1, it was less efficient. Of the five enzymes, UGT93Y1 stood out because of its high in vivo and in vitro biotransformation rate. The identification of novel menthol glycosyltransferases from the tea plant opens new perspectives for the biotechnological production of menthyl glucoside.

Comparative Physicochemical and Biochemical Characterization of Small-Molecule Glucosides

“…Recently, biotechnological platforms based on whole-cell biotransformation have been developed, , allowing the production of large quantities of SMGs (Figure ), whose physiochemical and biochemical properties have been analyzed in detail in this study.…”

Genome-wide identification of UDP-glycosyltransferases in the tea plant (Camellia sinensis) and their biochemical and physiological functions

“…However, tea UGTs not only glucosylate phenolics including flavonoids, in recent years a number of CsUGTs have also been functionally characterized that glycosylate plant volatiles ( Jiang et al., 2018 ; Chen et al., 2020 ; Jing et al., 2020 ; Zhao et al., 2020a ; Zhao et al., 2020b ; Kurze et al., 2021 ; Zhao et al., 2022 ). Plants produce airborne signalling metabolites such as ( Z )-3-hexenol in response to herbivore attack ( Wei and Kang, 2011 ).…”

“…Although menthol, an important aroma chemical, has not previously been found as a natural constituent of the tea plant, CsUGT93Y1 and CsUGT93Y2 were identified as (+/-)-menthol glucosyltransferases in a whole-cell biotransformation screen ( Kurze et al., 2021 ). The results demonstrate once again that several enzymes involved in the transformation of secondary metabolites exhibit substrate promiscuity.…”