Sialyl Lewis X (sLeX), also called cluster of differentiation 15s (CD15s) or stage-specific embryonic antigen-1 (SSEA-1), is a tetrasaccharide carbohydrate that plays a critical role in cell-cell recognition and adhesion. It consists of four monosaccharide units: N-acetylneuraminic acid (sialic acid), galactose, fucose, and N-acetylglucosamine, arranged in a specific branched configuration. This structure serves as the minimal recognition motif for the selectin family of cell adhesion molecules, making it fundamentally important in both physiological and pathological processes.
The antigen was first identified in the context of blood group biochemistry and later recognized as a crucial mediator of leukocyte trafficking during inflammation. Its expression on cell surfaces is tightly regulated by the coordinated action of multiple glycosyltransferases, particularly fucosyltransferases (FUT3, FUT4, FUT5, FUT6, FUT7) and sialyltransferases (ST3GAL3, ST3GAL4, ST3GAL6).
The sialyl Lewis X epitope has a well-defined branched structure [Neu5Acα2-3Galβ1-4[Fucα1-3]GlcNAcβ]. The core consists of a Type 2 lactosamine unit (Galβ1-4GlcNAc), which is modified by the addition of an α2,3-linked sialic acid to the galactose residue and an α1,3-linked fucose to the N-acetylglucosamine residue. This specific arrangement creates a three-dimensional conformation that is recognized by selectins.
- Tumor-associated carbohydrate antigen (TACA) and inflammation marker
- Applications: E-selectin, Siglec targeting
- Free -NH2 allow conjugation to biomolecules
