Lectin

Lectin

Lectins are sugar-binding proteins which are highly specific for their sugar moieties. 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 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.

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 or glycolipid. They typically agglutinate certain animal cells and/or precipitate glycoconjugates.

Function in animals

Lectins serve many different biological functions in animals, from the regulation of cell adhesion to glycoprotein 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 the lysosomes. 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 on pathogens, or that are inaccessible on host cells. Examples are the lectin complement activation pathway and Mannose 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-knockout transgene 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 of glycoproteins 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 typingFact|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, the anterograde labeling method is used to trace the path of efferent axons with PHA-L, a lectin from the kidney 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 or concanavalin 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 many crystal 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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Look at other dictionaries:

  • lectin — [lek′tin] n. [coined (1954) < L lectus, pp. of legere, to select + IN1] any of several proteins, found in plants and animals, that bind to specific sugar molecules, as on cancer or red blood cells …   English World dictionary

  • Lectin — Hemagglutinin lateral Lektine sind komplexe Proteine oder Glykoproteine, die spezifische Kohlenhydratstrukturen binden und dadurch in der Lage sind, sich spezifisch an Zellen bzw. Zellmembranen zu binden und von dort aus biochemische Reaktionen… …   Deutsch Wikipedia

  • lectin complement pathway — (lek tin) The lectin pathway for complement activation is triggered by the binding of a serum lectin (mannan binding lectin; MBL) to mannose containing proteins or to carbohydrates on viruses or bacteria …   Dictionary of microbiology

  • lectin pathway — a pathway of complement activation initiated in the absence of antibody by the binding of mannose binding lectin (MBL) to carbohydrates on the surface of microorganisms. MBL in turn activates complement component C4; the rest of the steps are the …   Medical dictionary

  • lectin — noun Etymology: Latin lectus (past participle of legere to pick, select) + 1 in more at legend Date: 1954 any of a group of proteins especially of plants that are not antibodies and do not originate in an immune system but bind specifically to… …   New Collegiate Dictionary

  • lectin — Proteins obtained particularly from the seeds of leguminous plants, but also from many other plant and animal sources, that have binding sites for specific mono or oligosaccharides. Named originally for the ability of some to selectively… …   Dictionary of molecular biology

  • lectin — /lek tin/, n. Biochem. any of a group of proteins that bind to particular carbohydrates in the manner of an antibody and are commonly extracted from plants for use as an agglutinin, as in clumping red blood cells for blood typing. [1954; < L… …   Universalium

  • lectin — noun Any of a class of plant proteins that bind specific carbohydrates …   Wiktionary

  • lectin — Any of a group of glycoproteins of primarily plant (usually seed) origin that binds to glycoproteins on the surface of cells causing agglutination, precipitation, or other phenomena resembling the action of specific antibody; lectins include… …   Medical dictionary

  • Lectin — Lec|tin [lat. legere, lectum = lesen, auflesen, auslesen; ↑ in (3)], das; s, e; S: Lektin; veraltete Syn.: Phytagglutinin, Phyt[o]hämagglutinin (PHA), Protektin, Toxalbumin: Sammelbez. für hochmol. Glykoproteine pflanzlicher, mikrobieller oder… …   Universal-Lexikon

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