Carbohydrate peanut lectin

Polymer adsorption has also been adapted to QCM sensing whereby biofunctional thin films are adsorbed on the crystal surface with non-specific binding controlled by tuning of polymer composition. This approach proved successful as applied to carbohydrate-protein interaction by Matsuura et al. through adsorption of lactose bearing amphiphilic polymers on hydrophobic surfaces which then showed RCA12o and peanut lectin (PNA) affinity [33]. Carbohydrate surfaces prepared by photo insertion into an adsorbed polymer were tested by QCM and showed the predicted affinities [34] while in another example a covalently bound glycopolymer demonstrated Concanavalin A detection ability [35]. 

The peanut Arachis hypogaea) contains a lectin with anti-T (Gal(Pl-3)GalNAc) activity [174]. This antigen appears on human erythrocytes following treatment with sialidase and leads to the phenomenon known as polyagglutinability as monitored by the peanut lectin [175]. Peanut agglutinin, purified by numerous affinity purification schemes, is a tetrameric protein composed of four carbohydrate-free subunits, A/f = 27000Da[176]. The lectin is a metalloprotein rich in acidic and hydroxylic amino acids and devoid of cysteine [176]. 

An example of the possibilites of the use of these techniques in the future is the paper by Stoward, Spicer, and Miller (1980) in which they use a peanut lectin— PAPS technique to identify galactose as the sub-terminal group, following removal of sialic acid with neuraminidase in, for example, the secretory glycoprotein in mouse duodenal cells. With the number of lectins now available commercially, some of which can be obtained with a PAPS label already attached, it can be anticipated that the histochemical sequencing of carbohydrate chains is well within the realm of possibility in the near future. 

Figure 35.20 Screening a library of synthesized carbohydrates, A small combinatorial library of carbohydrates synthesized on the surface of BO-jxm beads is screened for carbohydrates that are bound tightly by a lectin from peanuts. Beads that have such carbohydrates are darkly stained through the action of an enzyme linked to the lectin. [From R. Liang et al., Proc Nati. Acad Sci. USA 94(1997) 10554-10559 2004 National Academy of Sciences. USA.]...

Carbohydrate chains of Cl-inhibitor were identified by a binding assay using different lectins [36]. Lectins from Sambucus nigra (SNA) and Maackia amurensis (MAA), that are specific for sialic acids, were shown to bind to Cl-inhibitor. Lectin from Datura stramonium (DSA) also reacted with the inhibitor indicating complex and hybrid sugar structures. Cl-inhibitor was enzymatically desialylated and reexamined for lectin binding. SNA and MAA did not react anymore, but in addition to DSA, peanut agglutinin, which can bind to carbohydrate chains after sialic acids are removed, bound to desialylated Cl-inhibitor. Cl-inhibitor contains about 30 sialic acid residues per molecule. SDS-... 

A listing of the X-ray crystal structure (arranged in chronological order) of plant lectins is presented in Table 2 commencing with the structure of concanavalin A at 3 A resolution [38,39]. Interestingly, it was not until 1989 that a definitive high resolution X-ray crystal structure of the concanavalin A-methyl a-D-mannopyranoside complex was elucidated [40], and the most recently reported is that of peanut agglutinin [41]. Reviews on carbohydrate-protein interactions are also worthy of note [42-45]. 

Besides these three major protein classes, plant lectins, also known as plant agglutinins, were shown to react with the carbohydrate moieties of IgE, inducing histamine release and thus causing allergy-like symptoms [42,43]. One 31 kDa peanut agglutinin was already identified as a lectin binding specifically to the IgE epitope [44]. 

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