UDP-Glucose 4-Epimerase and ß-1,4-Galactosyltransferase from the Oyster Magallana gigas as Valuable Biocatalysts for the Production of Galactosylated Products.

Uridine diphosphate galactose (UDP-galactose) is a valuable building block in the enzymatic synthesis of galactose-containing glycoconjugates. UDP-glucose 4-epimerase (UGE) is an enzyme which catalyzes the reversible conversion of abundantly available UDP-glucose to UDP-galactose. Herein, we described the cloning, expression, purification, and biochemical characterization of an unstudied UGE from the oyster Magallana gigas (MgUGE). Activity tests of recombinantly expressed MgUGE, using HPLC (high-performance liquid chromatography), mass spectrometry, and photometric assays, showed an optimal temperature of 16 °C, and reasonable thermal stability up to 37 °C. No metal ions were required for enzymatic activity. The simple nickel-affinity-purification procedure makes MgUGE a valuable biocatalyst for the synthesis of UDP-galactose from UDP-glucose. The biosynthetic potential of MgUGE was further exemplified in a coupled enzymatic reaction with an oyster-derived ß-1,4-galactosyltransferase (MgGalT7), allowing the galactosylation of the model substrate para-nitrophenol xylose (pNP-xylose) using UDP-glucose as the starting material.

Galactosylation of glycoconjugates using Pacific oyster ß-1,3-galactosyltransferases.

The Pacific oyster (Magallana gigas) exhibits an extensive diversity of N- and O-linked glycoconjugates, offering significant potential for biotechnological applications. Through genomic data mining, we have identified and characterized a suite of ß-1,3-galactosyltransferase enzymes, pivotal for the synthesis of glycan structures. Out of ten cloned gene candidates, six enzymes were successfully expressed recombinantly in Escherichia coli. Four of these enzymes exhibited measurable catalytic activity in the transfer of galactose to various acceptor substrates. Notably, MgB3GalT1 demonstrated the highest efficiency, achieving a 91.2 % conversion rate. This enzyme was proficient in glycosylating diverse glycan structures, including Core 2 O-glycans and several di-, tri-, and tetra-antennary complex N-glycan standards. Mass spectrometric analysis confirmed the successful modification of N-glycans. These findings open new approaches for utilizing oyster-derived enzymes in glycan-based therapeutics and molecular glycoengineering, highlighting their utility in synthetic applications and biotechnological advancements.

Discovery and Biochemical Characterization of the UDP-Xylose Biosynthesis Pathway in Sphaerobacter thermophilus.

The biosynthesis of UDP-xylose requires the stepwise oxidation/ decarboxylation of UDP-glucose, which is catalyzed by the enzymes UDPglucuronic acid dehydrogenase (UGD) and UDP-xylose synthase (UXS). UDPxylose biosynthesis is ubiquitous in animals and plants. However, only a few UGD and UXS isoforms of bacterial origin have thus far been biochemically characterized. Sphaerobacter thermophilus DSM 20745 is a bacterium isolated from heated sewage sludge, and therefore can be a valuable source of thermostable enzymes of biotechnological interest. However, no biochemical characterizations of any S. thermophilus enzymes have yet been reported. Herein, we describe the cloning and characterization of putative UGD (StUGD) and UXS (StUXS) isoforms from this organism. HPLC- and plate reader-based activity tests of the recombinantly expressed StUGD and StUXS showed that they are indeed active enzymes. Both StUGD and StUXS showed a temperature optimum of 70°C, and a reasonable thermal stability up to 60°C. No metal ions were required for enzymatic activities. StUGD had a higher pH optimum than StUXS. The simple purification procedures and the thermotolerance of StUGD and StUXS make them valuable biocatalysts for the synthesis of UDP-glucuronic acid and UDP-xylose at elevated temperatures. The biosynthetic potential of StUGD was further exemplified in a coupled enzymatic reaction with an UDP-glucuronosyltransferase, allowing the glucuronylation of the natural model substrate bilirubin.