Lewis X and sialyl Lewis X glycosphingolipids

Lewis X (Le(x)) and sialyl Lewis X (sLe(x)) are carbohydrate blood group antigens important in cell adhesion. On cell membranes, Le(x) and sLe(x) may be expressed on glycoproteins or glycosphingolipids (GSLs). The latter are complex macromolecules consisting of an oligosaccharide moiety covalently linked to a ceramide lipid tail. Similar to glycoproteins, Le(x) and sLe(x) glycans expressed on GSLs can be either simple or multifucosylated, complex, branched, long-chain oligosaccharides. Developmental changes in Le(x) and sLe(x) GSL expression may play a role in embryonic development and organogenesis. On neutrophils and platelets, sLe(x) GSLs may function as the physiologic ligand for endothelial E-selectin, mediating rolling of platelets and neutrophils along activated endothelium. Likewise, endothelial sLe(x) GSLs may function as ligands for L-selectin on lymphocytes. In lens, the age-dependent increase in Le(x) GSL expression may contribute to cataractogenesis via Le(x)-Le(x) homotypic adhesion, leading to spatial rearrangement of lens fibers and lens opacification, In malignancy, neoexpression of Le(x) and sLe(x) GSLs by many tumors may contribute to tumor metastasis via increased adherence to vascular endothelium and platelets. In hematopoietic cells, biosynthesis of Le(x) and sLe(x) GSLs reflects the action of multiple glycosyltransferases. Lewis(x) and sLe(x) GSLs may also be chemically synthesized where they have been very useful in structure-function studies of selectin recognition and binding.