The sugar-combining area of the galactose-specific toxic lectin of mistletoe extends beyond the terminal sugar residue: comparison with a homologous toxic lectin, ricin

Journal/Book: Carbohydrate Res. 254, 269-276. 1994;

Abstract: Viscumin (the major lectin of mistletoe extract), also known as ML-1,and ricin (RCA II) belong to a group of heterodimeric toxic lectinscomposed of an A chain, which inhibits protein synthesis, and a B chain,which mediates entry into the cell in a galactose-specific manner.Although most of the binding force for the association of viscumin withgalactose-containing ligands is generated by the nonreducing terminalgalactose residue, a particular hydroxyl group on the penultimate sugaralso appears to participate in the binding, suggesting that viscumin hasan extended combining site. In this paper, we give further examples ofaffinity enhancement by the hydroxyl group situated on the penultimatesugar next to the glycosidic linkage of the terminal galactose. Thestructure with highest affinity for viscumin thus far discovered isbeta-D-Gal-(1--> 2)-beta-D-Gal. In contrast to viscumin, ricin does nothave this extended binding area, as none of the disaccharides testedexhibited significant affinity enhancement. Author.

Keyword(s): CARBOHYDRATE-CONFORMATION

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