Engineering an O‐methyltransferase for the Regioselective Biosynthesis of Hesperetin Dihydrochalcone

Abstract

Directed evolution of the O‐methyltransferase ZgOMT from Zooshikella ganghwensis focusing on active site residues resulted in highly regioselective biocatalysts (regioisomeric ratios up to 99 : 1) for the preparation of the taste active hesperetin dihydrochalcone and related compounds. These newly constructed enzyme variants provide an attractive synthesis route for para‐methylation of catechol scaffolds, which is challenging to perform with high regioselectivity utilizing wild‐type O‐methyltransferases.

Novel Catechol O-methyltransferases from Lentinula edodes Catalyze the Generation of Taste-Active Flavonoids

“…called Yerba santa, growing in the wild in arid areas of Northwest Mexico or Southwest US . Recently, a number of studies demonstrated promising approaches to obtain hesperetin dihydrochalcone, hesperetin, or homoeriodictyol by selective O -methylation of their respective precursors, eriodictyol dihydrochalcone and eriodictyol. ,, …”

“…The majority of reported flavonoid-specific OMTs were described for plants, such as soybean (Glycine max), rice (Oryza sativa), or periwinkle (Catharanthus roseus), which showed biocatalytic activities for the modification of i.a. naringenin, quercetin, and eriodictyol. − Moreover, synthetic pathways have recently been developed by heterologous expression of plant genes in bacterial cell hosts to produce O -methylated flavonoids. , Flavonoid-specific OMTs outside the plant kingdom have been reported only to a lesser extent. − ,,, In particular, the presence of OMTs from higher fungi, such as Basidiomycota, has been scarcely described. However, results from genome sequencing of various white-rot fungi revealed the presence of genes putatively encoding OMTs, which may be involved in the O -methylation of monolignols to inhibit oxidative stress from their free hydroxy groups and facilitate peroxidase activity for lignin degradation .…”

“…Interestingly, the aglycone of NHDC, hesperetin dihydrochalcone, and the corresponding flavanone analogue hesperetin along with its regioisomer homoeriodictyol have been reported to possess taste-active properties as well. [12][13][14][15]10 NHDC is a semisynthetic compound, which is commonly produced by hydrogenation of the naturally occurring neohesperidin under alkaline conditions. 7 Through subsequent hydrolysis of the neohesperidose sugar moiety, hesperetin dihydrochalcone can be formed.…”

Engineering a Plant Polyketide Synthase for the Biosynthesis of Methylated Flavonoids

“…coli . Lastly, Kunzendorf et al recently engineered a bacterial OMT for the regiospecific methylation of eriodictyol dihydrochalcone to hesperidin dihydrochalcone and eriodictyol to hesperetin in vitro , with 99:1 and 98:2 regioisomeric ratios, respectively . All of these strategies depend on the preassembled flavonoid scaffold that is either extracted from plant material or built de novo in a microbial cell factory.…”

Application of the C3-Methyltransferase StspM1 for the Synthesis of the Natural Pyrroloindole Motif

“…Focusing on the synthesis of the pyrroloindole structural motif in these natural compounds, a methyltransferase is needed for this key step in the biosynthetic pathway. , In nature, S -adenosyl methionine (SAM, 5 ) is used as a methyl donor for SAM-dependent methyltransferase reactions. The methyl group of SAM ( 5 ) can be transferred by these methyltransferases to a large variety of acceptor molecules, such as small metabolites or even biopolymers, whereby S -adenosyl-homocysteine (SAH) ( 6 ) is formed as the byproduct. − Methyltransferases can be further classified according to the atom on the substrate accepting the methyl group. Based on this classification, C -methyltransferases are comparatively rare (18%) …”