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, source
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.
Lectin and Cancer Prevention or
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.
Saracin: A lectin from Saraca indica seed integument induces apoptosis in human T-lymphocytes.
Lectin and the Immune System
Lectins affect the immune system by altering the production of various interleukins, or by activating certain protein kinases.
l-Type lectin from the kuruma shrimp Marsupenaeus japonicus promotes hemocyte phagocytosis. Dev Comp Immunology. 2014.
Dangers of excess
Alternative Therapies Health Medicine. 2015. Lectins, Agglutinins, and Their Roles in Autoimmune Reactivities. Lectins are carbohydrate-binding proteins present throughout nature that act as agglutinins. Approximately 30% of our food contains lectins, some of which may be resistant enough to digestion to enter the circulation. Because of their binding properties, lectins can cause nutrient deficiencies, disrupt digestion, and cause severe intestinal damage when consumed in excess by an individual with dysfunctional enzymes. These effects are followed by disruption of intestinal barrier integrity, which is the gateway to various autoimmunities. Shared amino acid motifs between dietary lectins, exogenous peptides, and various body tissues may lead to cross-reactivity, resulting in the production of antibodies against lectin and bacterial antigens, followed by autoimmunity. The detection of immunoglobulin G (IgG) or immunoglobulin A (IgA) antibodies against specific lectins may serve as a guide for the elimination of these lectins from the diet. It is proposed that this process can reduce the peripheral antigenic stimulus and, thereby, result in a diminution of disease symptoms in some-but not all-patients with autoimmune disorders.