Glycome Atlas
protein
Also known as glycan-binding proteins, carbohydrate-binding proteins
Plain-language answer
Lectins are proteins that read the sugar coatings on cells. Instead of cutting or building sugars, they simply recognize and grab onto specific sugar shapes, a bit like a key fitting a lock. Cells and microbes are covered in these sugar patterns, so lectins act as the molecules that let one cell sense the sugar identity of another.12
Because lectins recognize sugar patterns, they help the immune system tell healthy self-tissue from microbes and damaged cells. They guide immune cells to sites of inflammation, trigger or calm immune responses, and are exploited by many viruses and bacteria to attach to us. Understanding lectins helps explain how the body uses its sugar code to make decisions.1
Technical detail
Lectins are a broad, structurally diverse class of glycan-binding proteins that bind carbohydrate ligands with defined specificity through carbohydrate-recognition domains, mediating recognition rather than catalytic modification of their target glycans.1
A lectin is operationally defined as a glycan-binding protein that is neither an antibody nor an enzyme acting on the bound sugar. Recognition is achieved through carbohydrate-recognition domains that read the identity, linkage, and presentation of monosaccharides. Individual lectin-glycan interactions are typically of modest affinity, so avidity is amplified by multivalent binding when lectins oligomerize or when ligands are clustered on a surface.1
Animal lectins are organized into families by the fold and metal dependence of their recognition domains, including the C-type lectins, the sialic-acid-binding I-type lectins known as siglecs, the beta-galactoside-binding galectins, and the selectins that direct leukocyte trafficking. Plant and microbial lectins form additional groups and are widely used as laboratory reagents for detecting glycans.1
Endogenous lectins translate the information carried by cell-surface glycans into cellular responses. They mediate cell-cell adhesion, clearance of aged or misfolded glycoproteins, intracellular glycoprotein trafficking, and the innate and adaptive immune recognition of self and non-self glycan patterns. Many pathogens display or exploit lectins to adhere to host tissue, making lectin-glycan recognition central to both defense and infection.12
Human relevance
Distinct lectin families set the balance of immune activation and restraint by reading glycan patterns, so their recognition activity contributes mechanistically to inflammatory and regulatory responses.1
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