Lectin

Lectins are complex proteins or glycoproteins that bind specific carbohydrate structures and therefore are able to specifically bind to cells or cell membranes, and from there induce biochemical reactions. However, they do not exert enzymatic activity.

Lectins (Latin legere, to read ',' select ' ), various metabolic processes such as cell division, ribosomal protein, agglutination of cells (in terms of red blood cells is the hemagglutination ) or affect the immune system.

Lectins are widespread. They can be made from animals, plants or microorganisms.

Classification

Among the lectins include N- acetylglucosamine -binding Gramineae lectins, the chitin -binding Solanaceae lectins, the group of legume lectins and mannose -binding lectins from Amaryllidaceae, Alliaceae and Orchidaceae. The lectins from Aegopodium podagraria, Eranthis hyemalis and Urtica dioica are previously assigned to any group. In addition, many other lectins known.

Lectins to include some AB toxins such as high molecular weight Samenglykoproteide as ricin or bacterial toxins Shiga toxin, Vero toxin, diphtheria toxin, exotoxin A or alpha- sarcin. Abrin, ricin, phasins (after Phaseolus vulgaris, the common bean, Red kidney bean lectin, Erythroagglutinin, PHA -E, phaseolin ) and IgSF (English I- type lectins, I type lectins '), calnexin and calreticulin are different lectins. An example of a lectin is concanavalin A sugar residue from the seeds of Canavalia ensiformis jack bean.

Functions and effects

Agglutination and toxicity

Lectins of plant origin are found in vegetables, so that the human digestive tract is exposed to lectins regularly. These lectins can be toxic to humans or pets in a raw state and only become irreversibly inactivated by boiling. Cultured vegetables (eg green beans ) with such toxic lectins can only be consumed cooked.

The toxicity of these lectins is, inter alia, that they clump red blood cells and as a result of hemagglutination vessels can become clogged. From a certain quantity that leads to headaches, vomiting, diarrhea, and stomach and intestinal problems, in extreme cases, the consumption fatal. In particularly lektinreichen species, such as red beans, four or five raw seeds can already cause the first symptoms in adults. Symptoms of poisoning appear rapidly one, usually one to three hours after eating and usually disappear just as quickly - about three to four hours after the onset.

Other lectins are resistant to heat.

Some lectins are non-toxic, such as lectins from potato.

Antibiotic effect

In their mode of action similar to lectins often the antibiotics. Thus, ricin is a potent inhibitor of ribosomal protein synthesis. Some of lectins are toxic to microorganisms and thus are used as pesticides against insects.

Messengers

Lectins are usually attached to the outer membrane surface. They also play a role in the communication and interaction of cells and organisms. They are involved in many recognition processes. So can attach to the roots of clover with the help of the lectin -polysaccharide interaction bacteria such as Rhizobium trifolii that. With the recognition of the symbiotic nodule bacteria and leguminous plants is possible and is therefore specific.

Similar detection mechanisms play a role in the fertilization of the human egg.

Germination

Lectins can in the context of ontogeny play a role. Through the germination process some plant lectins are inactivated.

Chaperone

Examples of lectins calnexin and calreticulin are serving as chaperones in protein folding.

IgSF

About 500 different proteins of the IgSF immunoglobulin family were predicted from bioinformatic analyzes of mammalian genomes. This includes the Siglec family ( sialic acid -binding immunoglobulin English -type lectins ), a sialic acid -binding lectins group.

Occurrence in legumes

The following table represents the lectin content of various legumes is (according to USFDA ):