Human cells produce a repertoire of sialoglycans with high structural and functional diversity that forms a subclass within the Glycome - the Sialome. The structural diversity of the Sialome derives from the chemically diverse sialic acid types (e.g. Neu5Ac, Neu5Gc, Neu5,9Ac2), linkage types (α2-3/6/8) produced by twenty sialyltransferase isoenzymes, and underlying glycan types that are utilized in a combinatorial manner for sialoglycan synthesis. The vast structural diversity of the Sialome is mirrored by its diverse biological functions on the molecular and cellular level such as regulating the biochemical properties of glycoproteins or cell-cell and cell-extracellular matrix interactions. Moreover, the Sialome is at the center of numerous molecular interactions with endogenous sialic acid-binding lectins such as the Siglecs that are vital for immune cell function. On the contrary, the Sialome is exploited by pathogens that express sialic acid-binding lectins to attach to host cells and aberrations of the Sialome are associated with autoimmunity, neurodegeneration and cancer.
Many functions of the Sialome, however, remain elusive and the fine binding specificities of sialic acid-binding lectins, such as the fourteen Siglec family members, to specific sialoglycan types in their natural glycan environment at the cell surface are poorly understood. We have developed a library of isogenic HEK293 cells through precise gene-editing/engineering with combinatorial knock-in/out of glycosyltransferase genes to display distinct features of the Sialome in the natural glycoconjugate context. This cell-based sialoglycan array is used to dissect the fine binding specificities of sialic acid-binding lectins in the natural glycan context at the cell surface. We will present our genetic engineering platform for the cellular display of the human Sialome and its interactions with sialic acid-binding proteins with particular focus on the immunommodulatory Siglec family.