A lectin is a sugar-binding protein that agglutinates cells or precipitates glycoconjugates. A lectin molecule contains at least two sugar-binding sites. The specificity of a lectin is usually defined by the monosaccharides or oligosaccharides that are best at inhibiting the agglutination or precipitation the lectin causes.
Where is a Lectin found?
A lectin is a sugar-binding protein. Lectins have been found in
plants, viruses, microorganisms and animals, but despite their ubiquity,
their function in nature is unclear. Although lectins share the common
property of binding to defined sugar structures, their roles in various
organisms are not likely to be the same.
Plant Lectin
Plant lectins, a unique group of proteins and
glycoproteins with potent biological activity, occur in foods like wheat, corn,
tomato, peanut, kidney bean, banana, pea, lentil, soybean,
mushroom, rice, and
potato. Thus, dietary intakes by humans can be significant. Many lectins resist
digestion, survive gut passage, and bind to gastrointestinal cells and/or enter
the circulation intact, maintaining full biological activity.
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Lectin and Cancer Prevention or
Treatment
Several lectins
have been found to possess anticancer properties; they are used as therapeutic agents, preferentially binding to
cancer cell membranes or their receptors, causing cytotoxicity, apoptosis, and
inhibition of tumor growth. These compounds can become internalized into cells,
causing cancer cell agglutination and/or aggregation. Ingestion of lectins also
sequesters the available body pool of polyamines, thereby thwarting cancer cell
growth. Lectins can also
downregulate telomerase activity and inhibit angiogenesis.
Lectin and the Immune System
Lectins affect the immune system by altering the production of various
interleukins, or by activating certain protein kinases.