Lectin importance

CARVALHO M R, SGARBiERi V 0 (1998) Relative importance of phytohemagglutinin (lectin) and trypsin-chymotrypsin inhibitor on bean (Phaseolus vulgaris L) protein absorption and utilization by the rat. JNutr Sci Vitaminol (Tokyo). 44 685-96. 

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. 

Elevated ET-1 in SCA patients, even in the steady state, may play an important role in the dehydration of sickle erythrocytes and the resulting enhanced intra-erythrocytic HbS polymerization. Indeed, it has been shown that ET-1 activates Ca2+- gated K+ channels in mouse erythrocytes [34]. ET-1, as a pro-inflammatory agonist, has been shown to induce the production of inflammatory cytokines by monocytes. One of the cytokines, namely TNFa enhances the adherence of sickle erythrocytes to vascular endothelium [35]. In addition, endothehns upregulate the expression of endothelial adhesion molecules such as ICAM-l, VCAM-1 and E-se-lectin, which participate in the recruitment of white cells to the site of inflammation. The overall conclusions that can be drawn from these data is that ET-1 plays a critical role in the vasospasm and inflammation that result in VOC. The major effect of HU in ameliorating the clinical symptoms of SCA likely results from its ability to inhibit the chronically activated ET-1 expression in SCA patients. 

Both of these observations are accounted for in the schematic representation in Fig. 3C and D of SBA crosslinked with Tn-PSM under saturation conditions. The schematic shows individual SBA molecules crosslinked to four different Tn-PSM molecules. Importantly, to form the crosslinked complex shown in Fig. 3D, lectin molecules bind to aGalNAc residues on all four sides of a Tn-PSM polypeptide chain. This allows staggering of individual SBA molecules along the Tn-PSM polypeptide chain, with concomitant decrease in steric interactions between lectin molecules. This is important, since calculations of the density of SBA molecules bound to Tn-PSM (knowing the diameter of SBA from X-ray crystal studies50 and the length of the Tn-PSM polypeptide chain) suggests that only 300 SBA tetramers can bind to the same side of a Tn-PSM polypeptide chain, which is less than the 540 bound monomers of SBA and 833 bound... 

Importantly, the internal diffusion model for lectins binding to mucins is distinct from the classical lock and key model of ligand binding to a receptor. The internal... 

Ebola-gp 1, or Dengue-gp E. DC-SIGN is also known to oligomerize, and it is therefore particularly important to understand the intrinsic binding and multivalent binding requirements of this lectin. 

Retention of native carbohydrate structure also is important in applications that utilize the conjugated polysaccharide in binding studies with receptors or lectins. In these cases, the carbohydrate should be modified at limited sites, preferentially only at its reducing end. Section 4.6 of this chapter discusses glycan conjugation techniques in greater detail. 

To remove excess lectin (particularly important if the 5-fold excess ratio is used), centrifuge the preparation at a minimum of 50,000g for 30 minutes to several hours (4°C), depending on the size of the particles and the amount of solution. Discard the supernatant, and resuspend the lectin-gold pellet in 0.01 M sodium phosphate, pH 7.4, containing 1 percent PEG. 

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