Plant lectin

Finally, the targeting of liposomal antitumour agents on a cellular level requires recognition units. As a simple and readily accessible model system, we chose the interaction of lectins (plant proteins) which have specific recognition sites for certain sugars. The well known lectin Concanavalin A is able to bind four... 

These interactions involve adhesion proteins called selectins, which are found both on the rolling leukocytes and on the endothelial cells of the vascular walls. Selectins have a characteristic domain structure, consisting of an N-terminal extracellular lectin domain, a single epidermal growth factor (EGR) domain, a series of two to nine short consensus repeat (SCR) domains, a single transmembrane segment, and a short cytoplasmic domain. Lectin domains, first characterized in plants, bind carbohydrates... 

Concanavalin A is a plant lectin from the jack bean (Canavalia ensiformis) which binds with high affinity to mannose residues of glycoproteins. Concanavalin A is known to stimulate the tyrosine kinase activity of the INSR (3-subunit with consecutive activation of kinases downstream the insulin receptor (IRS, PI 3-kinase). It is believed that Concanavalin A stimulates the activation and autophosphorylation of the INSR kinase through aggregation of the receptor, although the precise mechanism of action is unclear. 

The ability of PO to interact with the acetyl residues of chitin allows us to compare them with monovalent lectins (i.e. extensins) which when binding with hemicellulose are only affected in a medium with a high ionic strength (Brownleader et al., 2006). As a rule, POs are bound with the plant cell wall and act as its modifiers. Some POs can form complexes with an extensin of cell walls (Brownleader et al., 2006). Consequently, chitin-specific sites that are capable of interacting with polysaccharides exist in the molecules of PO, and these sites can resemble the membrane receptor binding sites or else be similar to the domains of heparinbinding proteins (Kim et al., 2001). 

Numerous lectins have been purified and are commercially available three plant lectins that have been widely used experimentally are listed in Table 47-7. Among many uses, lectins have been employed to purify specific glycoproteins, as tools for probing the glycoprotein profiles of cell surfaces, and as reagents for generating mutant cells deficient in certain enzymes involved in the biosynthesis of oligosaccharide chains. 

Table 47-7. Three plant lectins and the sugars with which they interact. ...

Some of the best investigated anti-nutrients are the enzyme inhibitors present in legumes and other plants. The Bowman-Birk and the Kunitz inhibitors of trypsin and other proteases are among the best characterized. In contrast to the non-specific and widespread influences of tannins and lectins (Carmona, 1996), the Bowman-Birk, Kunitz and other such inhibitors target specific enzymes. Corresponding with this, proteases and other digestive enzymes vary in sensitivity to the different inhibitors. 

LAVELLE E 0, GRANT G, PUSZTAI A, PFULLER u, o hagan d t (2000) Mucosal immunogenicity of plant lectins in mice. Immunology. 99 30-37. 

OVELGONNE J H, KONINKX J F, PUSZTAI A, BARDOCZ S, KOK W, EWEN S W, HENDRIKS H G, VAN DIJK J E (2000) Decreased levels of heat shock proteins in gnt epithelial cells after exposure to plant lectins. Gut. 46 679-87. 

PUSZTAI A, BARDOCZ s (1996) Biological effect of plant lectins on the gastrointestinal tract Metabolic conseqnences and applications. Trends Glycosci Glycotech. 8 149-65. 

Crude chloroform-methanol-water (30 60 8, v/v) extracts of immunostainedTLC bands were analyzed without further purification by nanoelectrospray low-energy mass spectrometry. The authors showed that this effective PLC/MS-joined procedure offers a wide range of applications for any carbohydrate-binding agents such as bacterial toxins, plant lectins, and others. Phenyl-boronic acid (PBA) immobilized on stationary support phases can be put to similar applications. This technology, named boronate affinity chromatography (BAC), consists of a chemical reaction of 1,2- and 1,3-diols with the bonded-phase PBA to form a stable... 

Lectins, glycoproteins known for their ability to agglutinate erythrocytes in vitro, are present in many types of plants, including beans. Some lectins are toxic. Lectins interact with certain carbohydrates in a specific way. Lectins are still being studied. It appears that lectins may be involved in recognition between... 

Balzarini J, Schols D, Neyts J, Van Damme E, Penmans W, De Clercq E. a-(1-3)- and a-(l-6)-d-mannose-specific plant lectins are markedly inhibitory to human immunodeficiency virus and cytomegalovirus infections in vitro. Antimicrob Agents Chemother 1991 35 410-416. 

Balzarini J, Neyts J, Schols D, Hosoya M, Van Damme E, Peumans W, De Clercq E. The mannose-specific plant lectins from Cymbidium hybrid and Epipactis helleborine and the (TV-acetylglucosamine)w-specific plant lectin from Urtica dioica are potent and selective inhibitors of human immunodeficiency virus and cytomegalovirus replication in vitro. Antiviral Res 1992 18 191-207. 

In addition to the aforementioned effects on paracellular drug transport, Ca2+ also plays an important role in the transcytosis of macromolecules. The entry of the plant lectins abrin, modeccin, and viscumin into Vero cells was inhibited in a Ca2+-free medium a well as in a Ca2+-containing medium containing verapamil and Co2+, both inhibitors of Ca2+ [217], Ca2+ is therefore required at a stage after the binding of the above lectins, perhaps in the fusion and exocytosis of membrane vesicles. 

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