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The name ‘lectin’ is derived from the Latin word legere, meaning ‘to select’.
Although they were first discovered more than 100 years ago in plants, they are now known to be present throughout nature.
It is generally believed that the earliest description of such a hemagglutinin was by Peter Hermann Stillmark in his doctoral thesis presented in 1888 to the University of Dorpat, (one of the oldest universities in czarist Russia). This hemagglutinin, which was also highly toxic, was isolated by Stillmark from seeds of the castor tree (Ricinus communis) and was named ricin.
Most of the lectins are basically non-enzymic in action and non-immune in origin. Lectins occur ubiquitously in nature. They may bind carbohydrate moiety as such free in solution or carbohydrate moiety which is a part of protein/particulate body. They agglutinate cells and/or precipitates glycoconjugates.
Function in animals
While the function of lectins in plants is believed to be the binding of glycoproteins on the surface of cells, their role in animals also includes the binding of soluble extracellular and intercellular glycoproteins.
For example, there are lectins found on the surface of mammalian liver cells that specifically recognize galactose residues. It is believed that these cell-surface receptors are responsible for the removal of certain glycoproteins from the circulatory system.
Another example is the mannose-6-phosphate receptor that recognizes hydrolytic enzymes containing this residue and subsequently targets these proteins for delivery to the lysosomes. (one defect in this particular system is known as I-cell disease.)
They serve many different biological functions from the regulation of cell adhesion to glycoprotein synthesis and the control of protein levels in the blood.
Lectins are also known to play important roles in the immune system by recognising carbohydrates that are found exclusively on pathogens, or that are inaccessible on host cells. Examples are the lectin complement activation pathway and Mannose binding lectin.
Function in plants
The real function of lectins in plants is still to be found - they are not necessary for rhizobia binding as mentioned above (ruled out with lectin-knockout transgene) and cell adhesion function as their sole purpose in plants also questionable.
Large presence in seeds (from which lectins are usually isolated) decreases with growth and suggests a great role in plant germination and perhaps in the seed's survival itself.
Use in science, medicine and technology
Clinical use in blood typing
Purified lectins are important in a clinical setting because they are used for blood typing. Some of the glycolipids and glycoproteins on an individual's red blood cells can be identified by lectins.
Use in studying carbohydrate recognition by proteins
Lectins from legume plants have been widely used as model systems to understand the molecular basis of how proteins recognize carbohydrates, because they are relatively easy to obtain and have a wide variety of sugar specificities. The many crystal structures of legume lectins have led to a detailed insight of the atomic interactions between carbohydrates and proteins.
Use in studying efferent axons
Use in biochemical warfare
Use in malaria treatment
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lectin". A list of authors is available in Wikipedia.|