Lectin 436414 223779212 2008-07-05T19:35:41Z Zorrobot 7218328 robot Modifying: [[cs:Lektiny]] '''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. [[Image:Hemagglutinin_lateral.jpg|thumb|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 [[Ricinus|castor tree (Ricinus communis)]] and was named [[ricin]]. ==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. [[Image:gs4 sugar all.png|thumb|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 [[glycoprotein]]s on the surface of parasitic cells, their role in animals also includes the binding of soluble extracellular and intercellular glycoproteins. 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. Another example is the [[mannose-6-phosphate]] receptor that recognizes hydrolytic enzymes containing this residue and subsequently targets these proteins for delivery to the [[lysosome]]s. (one defect in this particular system is known as [[I-cell disease]].) Lectins serve many different biological functions from the regulation of [[cell adhesion]] to glycoprotein synthesis and the control of protein levels in the [[blood]]. Lectins are also known to play important roles in the [[immune system]] by recognizing carbohydrates that are found exclusively on [[pathogen]]s, or that are inaccessible on host cells. Examples are the lectin [[mannan-binding lectin pathway|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. ==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, the [[anterograde labeling method]] is used to trace the path of [[efferent]] [[axon]]s with [[PHA-L]], a lectin from the [[kidney bean]].<ref name="Carlson">{{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 }}</ref> ===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. ==See also== * [[Concanavalin A]] * [[Phytohaemagglutinin]] ==References== <references/> * {{cite journal |author=Loris R, Hamelryck T, Bouckaert J, Wyns L |title=Legume lectin structure |journal=Biochim. Biophys. Acta |volume=1383 |issue=1 |pages=9–36 |year=1998 |pmid=9546043 |url=http://www.binf.ku.dk/~thamelry/publications/bba_review.pdf |format={{dead link|date=June 2008}} &ndash; <sup>[http://scholar.google.co.uk/scholar?hl=en&lr=&q=intitle%3ALegume+lectin+structure&as_publication=Biochim.+Biophys.+Acta&as_ylo=1998&as_yhi=1998&btnG=Search Scholar search]</sup>}} * 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 * {{cite journal |author=Ni Y, Tizard I |title=Lectin-carbohydrate interaction in the immune system |journal=Vet Immunol Immunopathol |volume=55 |issue=1-3 |pages=205–23 |year=1996 |pmid=9014318 |doi=10.1016/S0165-2427(96)05718-2}} * [http://www.eylabs.com EY Laboratories, Inc] World's largest lectin manufacturer. {{Lectins}} [[Category:Immunology]] [[Category:Carbohydrates]] [[Category:Proteins]] [[Category:Glycoproteins]] [[cs:Lektiny]] [[de:Lektin]] [[fr:Lectine]] [[he:לקטין]] [[nl:Lectine]] [[ja:レクチン]] [[no:Lektiner]] [[pt:Lectina]] [[ru:Лектины]] [[zh:凝集素]]