Abstract
Glucosyltransferases are versatile biocatalysts to chemically modify small molecules and thus enhance their water solubility and structural stability. Although the genomes of all organisms harbor a multitude of glucosyltransferase genes, their functional characterization is hampered by the lack of high-throughput in-vivo systems to rapidly test the versatility of the encoded proteins. We have developed and applied a high-throughput whole cell biotransformation system to screen a plant glucosyltransferase library. As proof of principle, we identified 25, 24, 15, and 18 biocatalysts transferring D-glucose to sotolone, maple furanone, furaneol and homofuraneol, four highly appreciated flavor compounds, respectively. Although these 3(2H)- and 2(5H)-furanones have extremely low odor thresholds their glucosides were odorless. Upscaling of the biotechnological process yielded titers of 5.3 and 7.2 g/L for the new to nature β-D-glucopyranosides of sotolone and maple furanone, respectively. Consequently, plant glucosyltransferase show stunning catalytic activities, which enable the economical production of novel and unexplored chemicals with exciting new functionalities by whole-cell biotransformation.
Highlights
Sotolone (4,5-dimethyl-3-hydroxy-2(5H)-furanone) is a naturally occurring chiral lactone of industrial significance and is considered a high impact aroma chemical (Fig. 1)[1]
Maple furanone was initially synthesized in 1957 and later identified in hydrolyzed soy protein in 1980, and has been named after its powerful maple-caramel aroma and taste, which is reminiscent of maple syrup[22]
Since furanones are potent flavoring agents, we envisioned the development of a biocatalytic process for the production of furanone glucosides based on E. coli whole-cell biocatalysts expressing recombinant plant uridine diphosphate-sugar dependent glycosyltransferases in cells (UGTs)
Summary
Sotolone (4,5-dimethyl-3-hydroxy-2(5H)-furanone) is a naturally occurring chiral lactone of industrial significance and is considered a high impact aroma chemical (Fig. 1)[1]. Sotolone was first described as a breakdown product of the amino acid threonine[5] and was later proposed as the flavor principle of seasonings prepared from plant protein hydrolysates[6] It has since been identified in many foods, including coffee, aged sake and rum, flor sherry, and wines[7,8,9,10,11,12]. Sugar conjugation results in increased stability and water solubility as consequence of enhanced polarity and has a major impact on biological activity and toxicity[37] Because of their sessile life style, plants have evolved different mechanisms to cope with environmental threats involving a large gene family of UGTs for detoxification of endogenous and exogenous substances[38,39]. Plants are a particular rich source of unexplored UGT genes
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