Analysis of sequence variation among legume lectins. A ring of hypervariable residues forms the perimeter of the carbohydrate-binding site.
Twelve plant lectins from the Papilionoideae subfamily were selected to represent a range of carbohydrate specificities, and their sequences were aligned. Two variability indices were applied to the aligned sequences and the results were analysed using the three-dimensional structures of concanavalin A and the pea lectin. The areas of greatest variability were located in the carbohydrate-binding site region, forming a perimeter around a well-conserved core. These residues are inferred to be specificity determining, in the manner of antibodies, and the most variable position corresponded to Tyr100 in concanavalin A, a known ligand contact residue. In addition to the five peptide loops known to form the binding site from crystallographic studies, a sixth segment with variable residues was located in the binding-site region, and this may contribute to oligosaccharide specificity. In their overall composition, the lectin sites resemble those of the sugar-transport proteins rather than antibodies. The prospects for modelling lectin binding sites by the methods used for antibodies were also assessed.
Young
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Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario, Canada.
Oomen
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D000595:Amino Acid Sequence; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D003208:Concanavalin A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007887:Fabaceae / Q000737:chemistry*; D014644:Genetic Variation; D037102:Lectins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D037121:Plant Lectins; D010946:Plants, Medicinal; D016415:Sequence Alignment; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
D037102:Lectins; D037121:Plant Lectins; D003208:Concanavalin A