An anti-a-like lectin of Rana catesbiana eggs showing unusual reactivity

Abstract

A lectin was isolated from Rana catesbiana eggs that agglutinated blood group A-erythrocytes but did not agglutinate blood group B- or O-erythrocytes. The lectin was purified by Sephadex G-75 gel filtration and by acrylamide gel electrophoresis at pH 4.3 and was proved to be homogeneous on electrophoresis, and the molecular weight was determined as 210 000. The specificity of A-like activity seems to direct towards three monosaccharide units: GalNAc α1 → 3(or 4)-Gal β1 → 4(or 3)GlcNAc β1 → R based on inhibition of A-like hemagglutination by various monosaccharides, oligosaccharides and glycolipids, and based on precipitin reaction with various glycolipids and glycoproteins with known structures. Uniquely, A-like agglutination was inhibited not only by α- N-acetylgalactosamine analogs but also by N-acetyllactosamine analogs. The lectin showed therefore, two correlated specificities: one directed towards α- N-acetylgalactosamine residue at the terminal, and the other towards the subterminal Gal β1 → 4 βGlcNAc ( N-acetyllactosaminyl) residue. The reactivity due to the N-acetyllactosamine structure which in also found in erythrocyte ganglioside and in H-active chain might be blocked by sialyl or α- L-fucosyl substitution at the terminal, as the reactivity appeared after elimination of these sugar residues. In the A structure the reactivity due to N-acetyllactosaminyl residue seems not to be blocked by the presence of α- N-acetylgalactosamine at the terminal as A-agglutination was strongly inhibited by N-acetyllactosamine and its analogs. Although the lectin showed a single band on electrophoresis under different conditions, there is a possibility that the lectin may be a mixture of two proteins with different specificities as mentioned above.