Isolation and Immunochemical Characterization of the <i>Euonymus europaeus</i> Lectin Receptor from the Major Sialoglycoprotein of Human O Erythrocytes

Abstract

Purified and desialized blood‐group‐M glycoprotein from human O erythrocytes precipitated with a lectin isolated from Euonymus europaeus seeds. The precipitation was inhibited completely by lacto‐N‐fucopentaose I and lactose. The H2 N‐terminal tryptic fragment of glycoprotein M (MT), containing most of carbohydrate and all fucose of glycoprotein M [Lisowska and Jeanloz (1973) Carbohydr. Res. 29 , 181 ‐ 191], did not precipitate with the lectin but did inhibit the precipitation. Reduced alkali‐labile oligosaccharides and glycopeptide containing alkali‐stable oligosaccha‐ride were isolated from the desialized MT glycopeptide by alkaline borohydride degradation and gel nitration. Only glycopeptide with the alkali‐stable oligosaccharide inhibited the precipitation and on a molar basis it was as active as glycopeptide MT‐ Both gave 50% inhibition at about 0.76 mM. Two desialized oligosaccharides obtained as hydrazinolysis products of glycoprotein M, were also as active as glycopeptide MT in the inhibition test. This shows that both oligosaccharides as well as alkali‐stable oligosaccharide linked to glycopeptide MT have determinants of the same structure. The chemical composition of alkali‐stable oligosaccharides and their pattern of inhibition of precipitation strongly suggest that l ‐fucose α1‐linked at the nonreducing end is an immuno‐dominant group and that grouping l ‐Fucα1 → DGal →(GlcNAc, Gal, Man) is present in their molecules. The inhibition of the precipitation by glycopeptide MT is in agreement with the presence of only one alkali‐stable oligosaccharide chain on the glycoprotein M molecule [Tomita, Furthmayr and Marchesi (1978) Biochemistry, 17 , 4756 ‐ 4770]. These results as well as the restriction of lectin receptor site to alkali‐stable oligosaccharide, show that glycopeptide MT is monovalent in the reaction with the lectin.