Modifying the Cell Surface Carbohydrate Code: From the Evolution of Enzyme Tools for Blood Antigen Removal to the Discovery of Drugs Aimed at Enzyme Targets in Cancer

Cell surface glycans make up an important mode of intercellular communication and the enzymes that assemble and degrade them are not only important targets for therapeutics, but also powerful tools for chemical glycobiology. Our recent work has explored 1) the use of engineered glycoside hydrolases for generating universal blood by antigen removal, 2) the identification of inhibitors to glycosyltransferases in cancer pathways, and 3) the development of engineered “glycosynthases” to assemble and probe the function of glycosaminoglycan structures.

We have previously demonstrated that blood antigen-cleaving glycoside hydrolases can be engineered as tools towards the generation of universal blood through the cleavage of carbohydrate blood group antigens. Identification and directed evolution of these enzymes is enabled by a strategy that involves high-throughput screening with a sensitive fluorescence based assay. Using a similar approach, creatively repurposed to assay for glycosyltransferase rather than glycoside hydrolase activity, we have developed a high-throughput screen for inhibitors targeting fucosyltransferase enzymes that are highly expressed in cancers. Such inhibitors have potential as therapeutics for certain cancers wherein these enzymes’ upregulated activity results in the assembly of carbohydrate structures (e.g. sialyl Lewis^X) involved in malignant processes including metastasis. In another focus, we are developing tools for chemoenzymatic glycan synthesis through mechanism-based engineering of “glycosynthase” enzyme biocatalysts to assemble specific glycosaminoglycan structures. A facile enzymatic synthesis of these glycans will enable glycobiologists to probe their interactions in processes such as neural development and cancer.