Cells undergo proliferation and apoptosis, migration and differentiation via a number of cell surface receptors, most of which are heavily glycosylated. This review discusses receptor glycosylation and the known roles of glycans on the functions of receptors expressed in diverse cell types. We included growth factor receptors that have an intracellular tyrosine kinase domain, growth factor receptors that have a serine/threonine kinase domain, and cell-death-inducing receptors. N- and O-glycans have a wide range of functions including roles in receptor conformation, ligand binding, oligomerization, and activation of signaling cascades. A better understanding of these functions will enable control of cell survival and cell death in diseases such as cancer and in immune responses.

The O antigen of enterotoxigenic Escherichia coli serotype O117 consists of repeating units with the structure [−D-GalNAcβ1–3-L-Rhaα1–4-D-Glcα1–4-D-Galβ1–3-D-GalNAcα1–4]_n. A related structure is found in E. coli O107 where Glc is replaced by a GlcNAc residue. The O117 and O107 antigen biosynthesis gene clusters are homologous and reveal the presence of four putative glycosyltransferase genes, wclW, wclX, wclY and wclZ, but the enzymes have not yet been biochemically characterized. We show here that the His₆-tagged WclY protein expressed in E. coli Lemo21(DE3) cells is an α1,4-Glc-transferase that transfers Glc to the Gal moiety of Galβ1–3GalNAcα-OPO₃-PO₃-phenoxyundecyl as a specific acceptor, and that the diphosphate moiety of this acceptor is required. WclY utilized UDP-Glc, TDP-Glc, ADP-Glc, as well as UDP-GlcNAc, UDP-Gal or UDP-GalNAc as donor substrates, suggesting an unusually broad donor specificity. Activity using GDP-Man suggested the presence of a novel Man-transferase in Lemo21(DE3) cells. Mutations of WclY revealed that both Glu residues of the Ex₇E motif within the predicted GT domain are essential for activity. High GlcNAc-transferase activities of WclY were created by mutating Arg194 to Cys. A triple mutant identical to WclY in E. coli O107 was identified as an α1,4-GlcNAc-transferase. Characterization of WclY opens the door for the development of antibacterial approaches.