Terminal α‐linked galactose rather than N‐acetyl lactosamine is ligand for bovine heart galectin‐1 in N‐linked oligosaccharides of glycoproteins

Abstract

Preference for the β‐anomer of galactose attributed to the bovine heart 14 kDa galectin‐1 (BHL‐14) was re‐examined using natural glycoproteins and artificially glycosylated proteins as ligands. Endogenous glycoproteins co‐purified with BHL‐14 during its affinity chromatographic isolation contained oligosaccharides bearing terminal α‐linked galactose (TAG) moieties and were superior even to laminin as ligands for homogeneous BHL‐14 obtained by high pressure liquid chromatography. Artificially glycosylated proteins prepared by covalent attachment of melibiose to proteins and containing TAG moieties were ligands for BHL‐14, unlike their lactose counterparts which contained β‐linked galactose. Enzymatic removal of TAG moieties from the following glycoproteins abolished their recognition by BHL‐14: (i) endogenous glycoproteins co‐purified with BHL‐14; (ii) mouse laminin; and (iii) bovine heart glycoproteins recognized by peanut agglutinin. Modification of TAG in laminin using galactose oxidase also rendered the glycoprotein inert towards BHL‐14. Desialylation of human IgG, bovine thyroglobulin or laminin failed to increase the affinity of BHL‐14 for these glycoproteins. Since removal of TAG or of sialic acid moiety exposed LacNAc (Gal β1→4 GlcNAc) in these glycoproteins, these results indicated that TAG, rather than LacNAc, is a ligand for BHL‐14 on N‐linked oligosaccharide chains of glycoproteins. Ready recognition of human IgA and jacalin‐binding human plasma glycoproteins and non‐recognition of human IgG suggested that T antigen (Galβ1→3 GalNAc) may also be ligand for galectin‐1. Copyright © 2002 John Wiley & Sons, Ltd.