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. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Look up moiety in Wiktionary, the free dictionary. ...

lateral hemagglutinine

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. Hemagglutinin, as depicted in a simplified molecular model. ... Image of Tartu street Tartu (German, Polish Dorpat, Russian Юpьeв Yuryev) is the second largest city of Estonia, with its population of 101,246 (the Population Census data is from 2000) in an area of 38. ... Hemagglutinin, as depicted in a simplified molecular model. ... Binomial name Ricinus communis The castor bean (Ricinus communis) is not a true bean, but a member of the Euphorbiaceae or spurge family. ... Castor beans The protein ricin (pronounced ) is a toxin from the castor bean (Ricinus communis). ...

Biological functions

Most of the 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.

An oligosaccharide (shown in grey) bound in the binding site of a plant lectin (Griffonia simplicifolia isolectin IV in complex with the Lewis b blood group determinant). Only a part of the oligosaccharide (central, in grey) is shown for clarity.

Function in animals

While the function of lectins in plants is believed to be the binding of glycoproteins on the surface of parasitic cells, their role in animals also includes the binding of soluble extracellular and intercellular glycoproteins. N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins[1]. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide backbones. ...

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. Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ...

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.) Mannose-6-phosphate (M6P) is a molecule bound by lectin in the immune system. ... Various organelles labeled. ... ML II is also referred to as inclusion-cell (I-cell) disease because waste products, thought to include carbohydrates, lipids, and proteins, accumulate into masses known as inclusion bodies. ...

Lectins serve many different biological functions from the regulation of cell adhesion to glycoprotein synthesis and the control of protein levels in the blood. Schematic of cell adhesion The study of cell adhesion is part of cell biology. ... For other uses, see Blood (disambiguation). ...

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. A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... A pathogen (from Greek pathos, suffering/emotion, and gene, to give birth to), infectious agent, or more commonly germ, is a biological agent that causes disease or illness to its host. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... Mannose binding lectin (MBL), also named mannose- or mannan-binding protein MBP, is an important factor in the innate immunity. ...

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. Soybean root nodules, each containing billions of Bradyrhizobium bacteria Rhizobia (from the Greek words riza = root and bios = Life) are soil bacteria that fix nitrogen (diazotrophy) after becoming established inside root nodules of legumes (Fabaceae). ... A transgene is a gene or genetic material which has been transferred by any of a number of genetic engineering techniques from one organism to another. ...

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. Not to be confused with Gemination in phonetics. ...

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^{[citation needed]}. 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.

PHA-L, a lectin from the kidney bean, is used by neuroscientists to trace the path of efferent axons. This usage is called the anterograde labeling method.^[1] Binomial name Lablab purpureus (L.) Sweet The Hyacinth Bean (Lablab purpureus, syn. ... Species Ulex argenteus Ulex boivinii Ulex borgiae Ulex cantabricus Ulex densus Ulex europaeus - Common gorse Ulex gallii - Western gorse Ulex genistoides Ulex micranthus Ulex minor - Dwarf gorse Ulex parviflorus Ref: ILDIS Version 6. ... Species About 140 species, including: Vicia bithynica (Bithynian Vetch) Vicia canescens Vicia cassubica (Danzig Vetch) Vicia cracca (Tufted Vetch) Vicia dumetorum Vicia faba (Broad Bean) Vicia hirsuta (Hairy Vetch) Vicia lathyroides (Spring Vetch) Vicia lutea (Yellow Vetch) Vicia narbonensis Vicia onobrychioides Vicia oroboides Vicia orobus (Upright Vetch) Vicia pannonica Vicia... Dry kidney beans The kidney bean is a medium-sized variety of the common bean (Phaseolus vulgaris) with dark red skin. ... Efferent nerve fibers carry information away from the brain. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ...

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. PHA may stand for: Potentially hazardous asteroid, Person (or People) Having AIDS. Polyhydroxyalkanoate, a type of biodegradable plastic Polyhydroxyaldehyde, a class of carbohydrate. ... Concanavalin A is a lectin protein from Jackbean (Canavalia ensiformis). ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

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, Castor beans The protein ricin (pronounced ) is a toxin from the castor bean (Ricinus communis). ... Castor beans The protein ricin (pronounced ) is a toxin from the castor bean (Ricinus communis). ...

• 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.

See also

• Concanavalin A
• Phytohaemagglutinin

Concanavalin A is a lectin protein from Jackbean (Canavalia ensiformis). ... Phytohaemagglutinin (PHA, or phytohemagglutinin) is a lectin found in plants, especially beans, in the highest concentrations in the red kidney bean (Phaseolus vulgaris). ...

References

1. ^ Carlson, Neil R. (2007). Physiology of Behavior, 9th ed.. Boston: Pearson Education, Inc., 144. ISBN 0-205-46724-5. 

• Loris R, Hamelryck T, Bouckaert J, Wyns L (1998). "Legume lectin structure". Biochim. Biophys. Acta 1383 (1): 9-36. PMID 9546043. 

• Sharon, N., Lis, H. Lectins, Second Edition (2003) Kluwer Academic

External links

• World of Lectin links maintained by Thorkild C. Bøg-Hansen
• Ni Y, Tizard I (1996). "Lectin-carbohydrate interaction in the immune system". Vet Immunol Immunopathol 55 (1-3): 205-23. PMID 9014318. 
• EY Laboratories, Inc World's largest lectin manufacturer.