Leloir Glycosyltransferases as Biocatalysts for Chemical Production

Glycosylation is a chemical transformation that is centrally important in all glycoscience and related technologies. Catalysts offering good control over reactivity and selectivity in synthetic glycosylations are much sought. The enzymes responsible for glycosylations in natural biosynthesis are sugar-nucleotide-dependent (Leloir) glycosyltransferases. Discovery-oriented synthesis and pilot batch production of oligosaccharides and glycosylated natural products have previously relied on Leloir glycosyltransferases. However, despite their perceived synthetic utility, Leloir glycosyltransferases are yet to see widespread application in industrial biocatalysis. Here we show progress and limitations in the development of Leloir glycosyltransferases into robust biocatalytic systems for use in glycosylations for chemical production. Obtaining highly active and stable (whole-cell) catalysts that can promote the desired glycosylation(s) coupled to an in situ sugar nucleotide supply remains a difficult problem. Optimizing glycosyltransferase cascade reactions for high process efficiency is another. Glycosylations of some natural products (e.g., flavonoids, terpenoids) involve acceptor substrate solubility as a special challenge for biocatalytic process design. Strategies to overcome these problems are illustrated from examples of integrated biocatalytic process development with this class of enzymes.