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Lectins are sugar-binding proteins which are highly specific for their sugar moieties. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl 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.

lateral hemagglutinine
lateral hemagglutinine

Contents

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). Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Tartu is the second largest City of Estonia. In contrast to Estonia's political and financial capital Tallinn, Tartu is often considered the intellectual Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending This hemagglutinin, which was also highly toxic, was isolated by Stillmark from seeds of the castor tree (Ricinus communis) and was named ricin. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses The castor oil plant, Ricinus communis, is a Plant Species of the Euphorbiaceae (the evolution of this plant family is relatively unexplored Ricin (ˈraɪ sɨn is a Protein Toxin that is extracted 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.
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. Not to be confused with Peptidoglycan. Glycoproteins are proteins that contain Oligosaccharide chains ( Glycans) covalently attached

For example, there are lectins found on the surface of mammalian liver cells that specifically recognize galactose residues. Galactose (Gal (also called brain sugar) is a type of Sugar which is less sweet than Glucose. 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. Mannose-6-phosphate (M6P is a molecule bound by Lectin in the Immune system. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. (one defect in this particular system is known as I-cell disease. Inclusion-cell (I-cell disease, also referred to as mucolipidosis II (ML II is so named because Waste products thought to include Carbohydrates Lipids )

Lectins serve many different biological functions from the regulation of cell adhesion to glycoprotein synthesis and the control of protein levels in the blood. Cellular adhesion is the binding of a cell to another cell or to a Surface or matrix. Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells such as nutrients and oxygen—and transports Waste products

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. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Examples are the lectin complement activation pathway and Mannose binding lectin. The Mannan-binding lectin pathway (also known as the Ali/Krueger Pathway is homologous to the Classical complement pathway. Mannose binding lectin (MBL also named Mannose - or Mannan -binding protein (MBP is an important factor in 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. Rhizobia (from the Greek words rhiza = root and bios = Life are Soil bacteria that fix Nitrogen ( Diazotrophy A transgene is a Gene or genetic material that 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. Germination is the process whereby growth emerges from a period of dormancy

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. A blood type (also called a blood group) is a classification of Blood based on the presence or absence of inherited Antigenic substances on the Some of the glycolipids and glycoproteins on an individual's red blood cells can be identified by lectins.

PHA-L, a lectin from the kidney bean, is used by neuroscientists to trace the path of efferent axons. Phytohaemagglutinin (PHA or phytohemagglutinin) is a Lectin found in plants especially Beans PHA actually consists of two closely related proteins called An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell This usage is called the anterograde labeling method. [1]

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. Concanavalin A is a Lectin Protein originally extracted from the Jack-bean Canavalia ensiformis. The many crystal structures of legume lectins have led to a detailed insight of the atomic interactions between carbohydrates and proteins. 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 (ˈraɪ sɨn is a Protein Toxin that is extracted from the castor bean ( Ricinus communis) Ricin is isolated from seeds of the castor oil plant and is a protein that comprises two domains,


See also

References

  1. ^ Carlson, Neil R. Concanavalin A is a Lectin Protein originally extracted from the Jack-bean Canavalia ensiformis. Phytohaemagglutinin (PHA or phytohemagglutinin) is a Lectin found in plants especially Beans PHA actually consists of two closely related proteins called (2007). Physiology of Behavior, 9th ed. . Boston: Pearson Education, Inc. , 144. ISBN 0-205-46724-5.  

External links

Dictionary

lectin

-noun

  1. (biochemistry) Any of a class of plant proteins that bind specific carbohydrates.
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