Isolation and properties of beta-galactoside binding lectins of calf heart and lung

Abstract

A soluble lectin which agglutinates trypsin-treated rabbit erythrocytes was purified from calf heart using affinity chromatography on asialofetuin-Sepharose. Its molecular weight was determined by gel filtration to be approximately 17,000. On polyacrylamide gel electrophoresis in sodium dodecyl sulfate, the predominant molecular species had a molecular weight of 9,000, suggesting that the lectin is a dimer. Binding studies performed with iodinated lectin revealed that neuraminidase-treated calf erythrocytes contained approximately 5 X 10(6) lectin binding sites per cell. Native calf and rabbit erythrocytes bound the lectin, but human and rat erythrocytes required neuraminidase and trypsin treatment, respectively, for lectin binding to occur. A number of saccharides, glycopeptides, and glycoproteins possess haptene inhibitory activity toward lectin binding to erythrocytes. The most potent of these have either galactose beta leads to galactose beta leads to, galactose beta N-acetylglucosamine beta leads to, or galactose beta leads to N-acetylglucosamine beta leads to sequences at their nonreducing termini. Lactose and galactose beta 1 leads to 3N-acetylgalactosamine are the next best haptenes. Finally, alpha-linked galactose residues and free galactose are very weak haptenes. The presences of a terminal sialic acid residue impairs haptene activity in all instances. Calf heart also contains a membrane-associated lectin which is very similar but not identical with the soluble lectin. A soluble beta-galactoside binding lectin was also isolated from calf lung. It has the same molecular size and subunit structure as the soluble heart lectin and is antigenically identical. In binding studies, the pattern of inhibition by various haptenes was the same for all three lectins.