ANOMER SPECIFICITY OF THE 14-KDA GALACTOSE-BINDING LECTIN - A REAPPRAISAL

A beta-anomer preference among galactosides has been attributed to the S-type 14 kDa galactose binding lectin. Here the anomeric preference of this lectin from bovine brain (BBL) is reexamined using inhibition of lectin-mediated haemagglutination, binding of the lectin to dot-blotted glycoproteins and affinity electrophoresis of the lectin through polysaccharide-containing gels. 1-O-methyl alpha-D-galactoside was 8 times better inhibitor of BBL than the corresponding beta-anomer. The terminal galactose in bovine thyroglobulin (exclusively alpha-linked) were also nearly 8 times more inhibitory than those in asialofetuin (exclusively beta-linked). The terminal alpha-galactose-containing endogenous glycoproteins of bovine brain were nearly 4 times better inhibitors of BBL than laminin. Removal of terminal alpha-galactose units by alpha-galactosidase fully abolished the BBL binding of thyroglobulin and endogenous glycoproteins. BBL was also sugar-specifically retarded by polyacrylamide gel containing guar galactomannan which bears only alpha-linked galactose. Data indicated that alpha-galactosides were sometimes better than their beta-anomers in binding to BBL. The significance of this observation to the physiological role of galactose-binding lectins is discussed.