Lewis X (Lex) is a fucosylated trisaccharide carbohydrate antigen that serves as a fundamental structural motif in mammalian glycobiology. Composed of galactose, fucose, and N-acetylglucosamine arranged in a characteristic branched configuration, Lewis X represents the core Type 2 Lewis antigen structure. Unlike its sialylated derivative (sialyl Lewis X), Lewis X lacks the terminal sialic acid residue, which significantly alters its biological properties and receptor interactions.
First identified in the context of blood group biochemistry, Lewis X gained prominence when it was recognized as Stage-Specific Embryonic Antigen 1 (SSEA-1), a marker of murine embryonic stem cells and early embryonic development. In the clinical laboratory, Lewis X is detected as CD15, a widely used marker for granulocytes and certain leukemias. The antigen occupies a central position in glycan biosynthesis, serving as a precursor for more complex structures including sialyl Lewis X and Lewis Y.
The Lewis X epitope consists of a Type 2 lactosamine core (Galβ1-4GlcNAc) decorated with an α1,3-linked fucose attached to the N-acetylglucosamine residue. This branched trisaccharide configuration creates a distinctive three-dimensional shape that is recognized by specific lectins and antibodies. The absence of sialic acid leaves the galactose residue with a free hydroxyl group at the C3 position, which can serve as an acceptor site for further glycan elaboration.
Glycan structure: Galβ1-4(Fucα1-3)GlcNAc
Plays important roles in cell recognition, development, and immunity. It’s one of several “Lewis antigens” .
- Trisaccharide antigen overexpressed on cancer cells.
- Applications: targeting of immune lectin DC-SIGN
- Free -NH2 allow conjugation to biomolecules
