- Lectin
Lectins are sugar-binding
proteins which are highly specific for their sugarmoieties . They typically play a role in biological recognition phenomena involving cells and proteins. For example, some bacteria use lectins to attach themselves to the cells of the host organism during infection.Etymology
The name "lectin" is derived from the Latin word "legere", meaning "to select".
History
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 byPeter Hermann Stillmark in his doctoral thesis presented in 1888 to the University ofDorpat , (one of the oldest universities in czaristRussia ). Thishemagglutinin , which was also highly toxic, was isolated by Stillmark from seeds of the castor tree (Ricinus communis) and was namedricin .Biological functions
Most lectins are basically non-enzymic in action and non-immune in origin. Lectins occur ubiquitously in nature. They may bind to a soluble carbohydrate or to a carbohydrate moiety which is a part of a
glycoprotein orglycolipid . They typically agglutinate certain animal cells and/or precipitateglycoconjugate s.Function in animals
Lectins serve many different biological functions in animals, from the regulation of
cell adhesion toglycoprotein synthesis and the control of protein levels in the blood. They may also bind soluble extracellular and intercellular glycoproteins.Some lectins are found on the surface of mammalian liver cells which 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 lectin is a receptor which recognizes hydrolytic enzymes containing
mannose-6-phosphate , and subsequently targets these proteins for delivery to thelysosome s.I-cell disease is one type of defect in this particular system.Lectins are also known to play important roles in the
immune system by recognizing carbohydrates that are found exclusively onpathogen s, or that are inaccessible on host cells. Examples are the lectin complement activation pathway andMannose binding lectin .Function in plants
The function of lectins in plants is still uncertain. Once thought to be necessary for
rhizobia binding, this proposed function was ruled out through lectin-knockouttransgene studies.The large concentration of lectins in plant seeds decreases with growth, and suggests a role in plant
germination and perhaps in the seed's survival itself. The binding ofglycoprotein s on the surface of parasitic cells is also believed to be a function.Use in science, medicine and technology
Use in medicine and medical research
Purified lectins are important in a clinical setting because they are used for
blood typing Fact|date=February 2008. Some of the glycolipids and glycoproteins on an individual's red blood cells can be identified by lectins.
* A lectin from "Dolichos biflorus" is used to identify cells that belong to the A1 blood group.
* A lectin from "Ulex europaeus" is used to identify the H blood group antigen.
* A lectin from "Vicia graminea" is used to identify the N blood group antigen.In neuroscience, theanterograde labeling method is used to trace the path ofefferent axon s withPHA-L , a lectin from thekidney bean .cite book
first= Neil R.
last= Carlson
year= 2007
month=
title= Physiology of Behavior, 9th ed.
pages= 144
location= Boston
publisher=Pearson Education, Inc.
id= ISBN 0-205-46724-5]Use in studying carbohydrate recognition by proteins
Lectins from legume plants, such as
PHA orconcanavalin A , 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 manycrystal structures of legume lectins have led to a detailed insight of the atomic interactions between carbohydrates and proteins.Use in biochemical warfare
One example of the powerful biological attributes of lectins is the biochemical warfare agent
ricin .Ricin is isolated from seeds of the castor oil plant and is a protein that comprises two domains,
* One is a lectin that binds cell surface galactosyl residues and enables the protein to enter cells.
* The second domain is an N-glycosidase that cleaves nucleobases from ribosomal RNA resulting in inhibition of protein synthesis and cell death.ee also
*
Concanavalin A
*Phytohaemagglutinin References
*
* Sharon, N., Lis, H. Lectins, Second Edition (2003) Kluwer Academic
External links
* [http://plab.ku.dk/tcbh/lectin-links.htm World of Lectin] links maintained by Thorkild C. Bøg-Hansen
*
* [http://www.eylabs.com EY Laboratories, Inc] World's largest lectin manufacturer.
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