1 Department of Biology, Centre for Applied Synthetic Biology, and Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke Street West, Montreal, Quebec, Canada H4B 1R6.
2 Department of Biology, Centre for Applied Synthetic Biology, and Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke Street West, Montreal, Quebec, Canada H4B 1R6; Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montreal, Quebec, Canada H4B 1R6; PROTEO, Quebec Network for Research on Protein Function, Structure, and Engineering, Quebec City, Quebec, Canada G1V 0A6. Electronic address: david.kwan@concordia.ca.

The sugar moieties of many glycosylated small molecule natural products are essential for their biological activity. Glycosyltransferases (GTs) are the enzymes responsible for installing these sugar moieties on a variety of biomolecules. Several GTs that are active on natural products are inherently substrate-promiscuous and thus serve as useful tools in manipulating natural product glycosylation to generate new combinations of sugar units (glycone) and scaffold molecules (aglycone) in a process called glycodiversification. It is important to have an effective screening tool to detect the activity of promiscuous enzymes and their resulting glycoside products. Towards this aim, we have developed a strategy for screening natural product GTs in a high-throughput fashion enabled by rapid isolation and detection of chromophoric or fluorescent glycosylated natural products. This involves a solvent extraction step to isolate the resulting polar glycoside product from the unreacted aglycone acceptor substrate and the detection of the formed glycoside by the innate absorbance or fluorescence of the aglycone moiety. Using our approach, we screened a collection of natural product GTs against a panel of precursors to therapeutically important molecules. Three GTs showed previously unreported promiscuity towards anthraquinones resulting in novel e-rhodomycinone glycosides. Considering the pharmaceutical value of the clinically used anthraquinone glycosides that are biosynthesized from an e-rhodomycinone precursor, and the significance that the sugar moiety has on the biological activity of these drugs, our results are of particular importance towards the glycodiversification of therapeutics in this class. The GTs identified and the novel compounds that they produce show promise towards new biocatalytic tools and therapeutics.