Glycome Atlas
protein
Also known as E-selectin, P-selectin, L-selectin
Gal (β1-4) → GlcNAc; Neu5Ac (α2-3) → Gal; Fuc (α1-3) → GlcNAc
How to read these diagrams (SNFG)
Each shape is a class of sugar and each colour a specific one. Structures read right to left, with the reducing end (the point of attachment) on the right.
Plain-language answer
Selectins are adhesion molecules that let white blood cells stick lightly to the vessel wall and roll along it, like a piece of tape that grabs and releases as it tumbles. There are three of them: one on white blood cells, one on the vessel lining, and one released quickly by activated vessels and platelets. Each one grabs a specific sugar tag on its partner cell.1
Selectin-driven rolling is the first step that lets immune cells leave the bloodstream and reach infected or injured tissue. This makes selectins central to normal defense and to inflammation. When rolling goes into overdrive, it fuels inflammatory disease, and tumor cells can borrow the same sugar tags to spread through the blood.1
Technical detail
Selectins are a family of three transmembrane calcium-dependent (C-type) lectins, encoded by SELE, SELP, and SELL, that bind sialylated fucosylated glycans such as sialyl-Lewis-x under flow to mediate leukocyte tethering and rolling as the first step of the leukocyte adhesion cascade.1
Each selectin shares an amino-terminal C-type lectin domain, an epidermal-growth-factor-like domain, and a series of consensus repeats. E-selectin is induced on activated endothelium, P-selectin is stored in Weibel-Palade bodies of endothelium and platelet granules for rapid surface display, and L-selectin is constitutively expressed on most leukocytes. Their calcium-dependent lectin domains recognize the sialyl-Lewis-x tetrasaccharide and closely related sialylated, fucosylated structures.1
Physiological binding requires that sialyl-Lewis-x be correctly presented on specialized glycoprotein scaffolds. The best-characterized ligand is P-selectin glycoprotein ligand-1 (PSGL-1), which additionally requires tyrosine sulfation for high-affinity P-selectin binding, illustrating that both the glycan and its protein context determine selectin engagement.1
Selectin-ligand bonds form and break rapidly and can strengthen transiently under shear as catch bonds, which allows leukocytes to tether and roll along the vessel wall against blood flow rather than detaching. Rolling slows the cell enough for chemokine signals to trigger integrin activation, firm arrest, and transmigration, placing selectins at the start of the multistep adhesion cascade.1
Human relevance
Selectin-mediated rolling is a required first step in recruiting leukocytes to inflamed tissue, and excessive or dysregulated selectin activity contributes mechanistically to inflammatory and thrombotic disease.1
Tumor cells that display selectin ligands such as sialyl-Lewis-x can engage selectins on endothelium and platelets, an interaction associated with hematogenous metastatic spread.1
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References