Anomer specificity of the 14 kDa galactose-binding lectin: A reappraisal

Abstract

A β-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. 1.0-methyl α-D-galactoside was 8 times better inhibitor of BBL than the corresponding s-anomer. The terminal galactose in bovine thyroglobulin (exclusively. α-linked) were also nearly 8 times more inhibitory than those in asialofetuin (exclusively s-linked). The terminal α-galactose-containing endogenous glycoproteins of bovine brain were nearly 4 times better inhibitors of BBL than laminin. Removal of terminal α-galactose units by α-galactosidase fully abolished the BBL binding of thyroglobulin and endogenous glycoproteins. BBL was also sugar-specifically retarded by polyacrylamide gel containing guar galactommannan which bears only α-linked galactose. Data indicated that α-galactosides were sometimes better than their β-anomers in binding to BBL. The significance of this observation to the physiological role of galactose-binding lectins is discussed.