Lectins are sugar-binding
proteinswhich 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.
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
hemagglutininwas by Peter Hermann Stillmarkin 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 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
glycoproteinor 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 adhesionto glycoproteinsynthesis 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
galactoseresidues. 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 diseaseis one type of defect in this particular system.
Lectins are also known to play important roles in the
immune systemby 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
rhizobiabinding, this proposed function was ruled out through lectin-knockout transgenestudies.
The large concentration of lectins in plant seeds decreases with growth, and suggests a role in plant
germinationand 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 "
Dolichosbiflorus" is used to identify cells that belong to the A1 blood group.
* A lectin from "
Ulexeuropaeus" is used to identify the H blood group antigen.
* A lectin from "
Viciagraminea" is used to identify the N blood group antigen.In neuroscience, the anterograde labeling methodis used to trace the path of efferent axons with PHA-L, a lectin from the kidney bean.cite book
first= Neil R.
title= Physiology of Behavior, 9th ed.
publisher=Pearson Education, Inc.
id= ISBN 0-205-46724-5]
Use in studying carbohydrate recognition by proteins
Lectins from legume plants, such as
PHAor 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 structuresof 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. Ricinis 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-
glycosidasethat cleaves nucleobases from ribosomal RNA resulting in inhibition of protein synthesis and cell death.
* Sharon, N., Lis, H. Lectins, Second Edition (2003) Kluwer Academic
* [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 — 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
lectin — n. any of a number of plant proteins that bind to particular carbohydrates (Biochemistry) … English contemporary dictionary
lectin — noun Biochemistry a protein which binds specifically to a sugar and causes agglutination of particular cell types. Origin 1950s: from L. lect , legere choose + in1 … English new terms dictionary