- Legume lectin
The legume lectins are a family of sugar binding proteins or
lectins found in theseeds and, in smaller amounts, in the roots, stems, leaves and bark ofplants belonging to the Fabaceaefamily [Sharon, N. & Lis, H. (1990) FASEB J., 4, 3198-3208] [Loris, R., Hamelryck, T., Bouckaert, J. & Wyns, L. (1998) Biochim.Biophys. Acta, 1383, 9-36] . The exact function of the legume lectins "in vivo" is unknown but they are probably involved in the defense of plantsagainst predators. Related proteins in other plant families and in animals have also been found. They have been used fordecades as a model system for the study of protein-carbohydrateinteractions, because they show an amazing variety of bindingspecificities and are easy to obtain and purify. Over the years, aquite impressive amount of structural data has been gathered [Loris, R., Hamelryck, T., Bouckaert, J. & Wyns, L. (1998) Biochim. Biophys. Acta, 1383, 9-36] . Well-studied members of this protein family include phytohemagglutininand concanavalin A.
ugar binding by legume lectins
The legume lectins use an ingenious framework for bindingspecific sugars. This framework consists of aconserved monosaccharide binding site in which four conserved residuesfrom four separate regions in the protein confer affinity (see figure), a variable loop that confers monosaccharidespecificity and a number of subsites around the monosaccharide bindingsite that harbor additional sugar residues or hydrophobic groups [Loris, R., Hamelryck, T., Bouckaert, J. & Wyns, L. (1998) Biochim. Biophys. Acta, 1383, 9-36] .
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