Lectin

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Lateral hemagglutinine

Lectins are carbohydrate-binding proteins, macromolecules that are highly specific for sugar moieties. Lectins should neither be confused with glycoproteins (proteins containing sugar chains or residues), lecithins (fatty substances in animals and plants), nor leptin, (the regulator of appetite and hunger, metabolism, and behavior). Long before a deeper understanding of their numerous biological functions, the plant lectins, also known as phytohemagglutinins, were noted for their particular high specificity for foreign glycoconjugates (e.g. those of fungi, invertebrates and animals).[1] and used in biomedicine for blood cell testing and in biochemistry for fractionation.

Lectins perform recognition on the cellular and molecular level and play numerous roles in biological recognition phenomena involving cells, carbohydrates, and proteins.[2][3] Lectins also mediate attachment and binding of bacteria and virus, as well as mediate the first-line defence against invading mictoorganisms with MBL, the mannan-binding lectin in the Innate immune system. It is hypothesized that some hepatitis C viral glycoproteins attach to C-type lectins on the host cell surface (liver cells) for infection.[4] Lectins may be disabled by specific mono- and oligosaccharides, which bind to ingested lectins from grains, legume, nightshade plants and dairy; binding can prevent their attachment to the carbohydrates within the cell membrane.[5] Some lectins may be powerful toxins as for instance ricin, and others have been incorporated into genetically engineered crops to transfer traits such as resistance to pests and resistance to herbicides.

Etymology[edit]

Table of the major lectins [6]
  Lectin SymbolLectin nameSourceligand motif
Mannose binding lectins
ConAConcanavalin ACanavalia ensiformisα-D-mannosyl and α-D-glucosyl residues

branched α-mannosidic structures (high α-mannose type, or hybrid type and biantennary complex type N-Glycans)

LCHLentil lectinLens culinarisFucosylated core region of bi- and triantennary complex type N-Glycans
GNASnowdrop lectinGalanthus nivalisα 1-3 and α 1-6 linked high mannose structures
Galactose / N-acetylgalactosamine binding lectins
RCARicin, Ricinus communis Agglutinin, RCA120Ricinus communisGalβ1-4GalNAcβ1-R
PNAPeanut agglutininArachis hypogaeaGalβ1-3GalNAcα1-Ser/Thr (T-Antigen)
AILJacalinArtocarpus integrifolia(Sia)Galβ1-3GalNAcα1-Ser/Thr (T-Antigen)
VVLHairy vetch lectinVicia villosaGalNAcα-Ser/Thr (Tn-Antigen)
N-acetylglucosamine binding lectins
WGAWheat Germ Agglutinin, WGATriticum vulgarisGlcNAcβ1-4GlcNAcβ1-4GlcNAc, Neu5Ac (sialic acid)
N-acetylneuraminic acid binding lectins
SNAElderberry lectinSambucus nigraNeu5Acα2-6Gal(NAc)-R
MALMaackia amurensis leukoagglutininMaackia amurensisNeu5Ac/Gcα2,3Galβ1,4Glc(NAc)
MAHMaackia amurensis hemoagglutininMaackia amurensisNeu5Ac/Gcα2,3Galβ1,3(Neu5Acα2,6)GalNac
Fucose binding lectins
UEAUlex europaeus agglutininUlex europaeusFucα1-2Gal-R
AALAleuria aurantia lectinAleuria aurantiaFucα1-2Galβ1-4(Fucα1-3/4)Galβ1-4GlcNAc,

R2-GlcNAcβ1-4(Fucα1-6)GlcNAc-R1

The name "lectin" is derived from the Latin word legere, meaning, among other things, "to select".(lek'tin)

History[edit]

Although they were first discovered more than 100 years ago in plants, lectins are now known to be present throughout nature. It is generally believed that the earliest description of a lectin was given by Peter Hermann Stillmark in his doctoral thesis presented in 1888 to the University of Dorpat. Stillmark isolated ricin, an extremely toxic hemagglutinin, from seeds of the castor plant (Ricinus communis). The first lectin to be purified on a large scale and available on a commercial basis was concanavalin A, which is now the most-used lectin for characterization and purification of sugar-containing molecules and cellular structures. The legume lectins are probably the most well-studied lectins.

Biological functions[edit]

Most lectins do not possess enzymatic activity and are not produced naturally by the immune system. Lectins occur ubiquitously in nature. They may bind to a soluble carbohydrate or to a carbohydrate moiety that 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.

Functions in animals[edit]

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 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 lectin is a receptor that recognizes hydrolytic enzymes containing mannose-6-phosphate, and 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.

Functions in plants[edit]

Leucoagglutinin, a toxic phytohemagglutinin found in raw Vicia faba

The function of lectins in plants (legume lectin) is still uncertain. Once thought to be necessary for rhizobia binding, this proposed function was ruled out through lectin-knockout transgene studies.[7]

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. Several plant lectins have been found to recognise non-carbohydrate ligands that are primarily hydrophobic in nature, including adenine, auxins, cytokinin, and indole acetic acid, as well as water-soluble porphyrins. It has been suggested that these interactions may be physiologically relevant, since some of these molecules function as phytohormones.[8] are another major family of protein ANCs, which are specific sugar-binding proteins exhibiting reversible carbohydrate-binding activities.

Lectins are similar to antibodies in their ability to agglutinate red blood cells; however, lectins are not immune system products. The toxicity of lectins has been identified by consumption of food with high lectin content, which can lead to diarrhea, nausea, bloating, vomiting, even death (as from ricin). Many legume seeds have been proven to contain high lectin activity, termed hemagglutinating activity. Soybean is the most important grain legume crop, the seeds of which contain high activity of soybean lectins (soybean agglutinin or SBA). SBA is able to disrupt small intestinal metabolism and damage small intestinal villi via the ability of lectins to bind with brush border surfaces in the distal part of small intestine.[citation needed] Heat processing can reduce the toxicity of lectins, but low temperature or insufficient cooking may not completely eliminate their toxicity, as some plant lectins are resistant to heat. (It is believed that undercooking red kidney beans increases toxicity.) In addition, lectins can result in irritation and over-secretion of mucus in the intestines, causing impaired absorptive capacity of the intestinal wall.[citation needed]

Use in science, medicine and technology[edit]

Use in medicine and medical research[edit]

Purified lectins are important in a clinical setting because they are used for blood typing.[9] Some of the glycolipids and glycoproteins on an individual's red blood cells can be identified by lectins.

In neuroscience, the anterograde labeling method is used to trace the path of efferent axons with PHA-L, a lectin from the kidney bean.[10]

A lectin (BanLec) from bananas inhibits HIV-1 in vitro.[11] Achylectins, isolated from Tachypleus tridentatus, show specific agglutinating activity against human A-type erythrocytes. Anti-B agglutinins such as anti-BCJ and anti-BLD separated from Charybdis japonica and Lymantria dispar, respectively, are of value both in routine blood grouping and research.[12]

Use in studying carbohydrate recognition by proteins[edit]

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 as a biochemical tool[edit]

Concanavalin A and other commercially available lectins have been widely used in affinity chromatography for purifying glycoproteins.[13]

In general, proteins may be characterized with respect to glycoforms and carbohydrate structure by means of affinity chromatography, blotting, affinity electrophoresis and affinity immunoelectrophoreis with lectins as well as in microarrays, as in evanescent-field fluorescence-assisted lectin microarray.[14]

Use in biochemical warfare[edit]

One example of the powerful biological attributes of lectins is the biochemical warfare agent ricin. The protein ricin is isolated from seeds of the castor oil plant and comprises two protein domains. Abrin from the jequirity pea is similar:

Toxicity[edit]

Digestion and immune distress[edit]

Foods with high concentrations of lectins, such as beans, cereal grains, seeds, nuts, and potatoes, may be harmful if consumed in excess in uncooked or improperly cooked form. Adverse effects may include nutritional deficiencies, and immune (allergic) reactions.[15] Possibly, most effects of lectins are due to gastrointestinal distress through interaction of the lectins with the gut epithelial cells. A recent in vitro study has suggested that the mechanism of lectin damage may occur by interfering with the repair of already-damaged epithelial cells.[16]

Lectin and Leptin Resistance[edit]

Lectin may cause leptin resistance, affecting its functions (signal have high levels of leptin and several effects gathering to protect from lipid overload), as indicated by studies on effects of single nucleotide polymorphisms on the function of leptin and the leptin receptor.[17] Such leptin resistance may translate into diseases, notably it could be responsible for obesity in humans who have high levels of leptin.

See also[edit]

References[edit]

  1. ^ Els. J. M. Van Damme, Willy J. Peumans, Arpad Pusztai, Susan Bardocz (March 30, 1998). Handbook of Plant Lectins: Properties and Biomedical Applications. John Wiley & Sons. pp. 7–8. ISBN 978-0-471-96445-2. Retrieved 18 April 2013. 
  2. ^ URS Rutishauser and Leo Sachs (May 1, 1975). "Cell-to-Cell Binding Induced by Different Lectins". Journal of Cell Biology (Rockefeller University Press) 65 (2): 247–257. Retrieved 28 April 2013. 
  3. ^ Matthew Brudner, Marshall Karpel, Calli Lear, Li Chen, L. Michael Yantosca, Corinne Scully, Ashish Sarraju, Anna Sokolovska, M. Reza Zariffard, Damon P. Eisen, Bruce A. Mungall, Darrell N. Kotton, Amel Omari, I-Chueh Huang, Michael Farzan, Kazue Takahashi, Lynda Stuart, Gregory L. Stahl, Alan B. Ezekowitz, Gregory T. Spear, Gene G. Olinger, Emmett V. Schmidt, and Ian C. Michelow1 (April 2, 2013). "Lectin-Dependent Enhancement of Ebola Virus Infection via Soluble and Transmembrane C-type Lectin Receptors". In Bradley S. Schneider. PLoS One. 8 (4 specific e code=e60838). doi:10.1371/journal.pone.0060838. PMC 3614905. Retrieved 18 April 2013. 
  4. ^ R. Bartenschlager, S. Sparacio (2007). "Hepatitis C Virus Molecular Clones and Their Replication Capacity in Vivo and in Cell Culture". Virus Research (Elsevier) 127 (2): 195–207. 
  5. ^ The Lectin Story
  6. ^ "Lectin list". Interchim. 2010. Retrieved 2010-05-05. 
  7. ^ http://www.annualreviews.org/doi/full/10.1146/annurev.arplant.59.032607.092839
  8. ^ Komath SS, Kavitha M, Swamy MJ (March 2006). "Beyond carbohydrate binding: new directions in plant lectin research". Org. Biomol. Chem. 4 (6): 973–88. doi:10.1039/b515446d. PMID 16525538. 
  9. ^ The History of Lectins by N.Sharon
  10. ^ Carlson, Neil R. (2007). Physiology of behavior. Boston: Pearson Allyn & Bacon. ISBN 0-205-46724-5. 
  11. ^ http://www.jbc.org/content/285/12/8646.abstract "A Lectin Isolated from Bananas Is a Potent Inhibitor of HIV Replication" 2010
  12. ^ http://www.tandfonline.com/doi/full/10.1080/11250003.2010.492794 Prospect for lectins in arthropods 2010
  13. ^ Immobilized Lectin
  14. ^ Glyco Station, Lec Chip, Glycan profiling technology
  15. ^ British Journal of Nutrition (2000), 83: 207-217 Cambridge University Press
  16. ^ Miyake K, Tanaka T, McNeil PL (2007). "Lectin-Based Food Poisoning: A New Mechanism of Protein Toxicity". In Steinhardt, Richard. PLoS ONE 2 (1): e687. doi:10.1371/journal.pone.0000687. PMC 1933252. PMID 17668065. 
  17. ^ T Jönsson, S Olsson, B Ahrén , T C Bøg-Hansen, A Dole and S Lindeberg (2005). "Agrarian diet and diseases of affluence – Do evolutionary novel dietary lectins cause leptin resistance?". BioMed Central Ltd.. doi:10.1186/1472-6823-5-10. . http://www.biomedcentral.com/1472-6823/5/10.

Further reading[edit]

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