Purification and characterization of Silurus asotus (catfish) roe lectin

A rhamnose-binding lectin isolated from Silurus asotus (catfish) roe by DEAE-cellulose ion exchange and galactose-Sepharose affinity chromatographies predominantly agglutinated human type B and rabbit erythrocytes. S. asotus lectin (SAL) also agglutinated sarcoma 180 ascites carcinoma cells, but not AH109A cells. The most effective saccharide in hemagglutination inhibition assay was L-rhamnose. The monosaccharides possessing steric similarity to the hydroxyl group orientation at C2 and C4 of the pyranose ring structure of L-rhamnose, such as L-mannose and L-lyxose, were also effective. The molecular weight of SAL was determined to be 38000 by size exclusion chromatography on TSK gel G3000SW and 33000 by SDS-polyacrylamide gel electrophoresis under reducing conditions. SAL did not require a Ca2+ ion or free thiol group for its agglutination activity. The N-terminal 29 amino acid sequence was determined by a gas-phase sequencer as follows, ANMITCYGDVQKLHXETGLIIVKSXLYGR (X: not determined). It has no homology to the sequences of well known vertebrate lectins.