Owing to the expression of more than one type of galectin in animal tissues
, the delineation of the functions of individual members of this lectin fam
ily requires the precise definition of their carbohydrate specificities. Th
us, the binding properties of chicken liver galectin (CG-16) to glycoprotei
ns (gps) and Streptococcus pneumoniae type 14 polysaccharide were studied b
y the biotin/avidin-mediated micro titre-plate lectin-binding assay and by
the inhibition of lectin-glycan interactions with sugar ligands. Among 33 g
lycans tested for lectin binding, CG-16 reacted best with human blood group
ABO (H) precursor gps and their equivalent gps, which contain a high densi
ty of D-galactopyranose(beta1-4)2-acetamido-2-deoxy-D-glucopyranose [Gal(be
ta1-4)GlcNAc] and Gal(beta1-3)GlcNAc residues at the nonreducing end, but t
his lectin reacted weakly or not at all with A-, H-type and sialylated gps.
Among the oligosaccharides tested by the inhibition assay, the tri-antenna
ry Gal(beta1-4)GlcNAc (Tri-II) was the best. It was 2.1 x 10(3) nM and 3.0
times more potent than Gal and Gal(beta1-4)GlcNAc (II)/Gal(beta1-3) GlcNAc(
beta1-3)Gal(beta1-4)Glc (lacto-N-tetraose) respectively. CG-16 has a prefer
ence for the beta -anomer of Gal at the nonreducing end of oligosaccharides
with a Gal(beta1-4) linkage > Gal(beta1-3) greater than or equal to Gal(be
ta1-6). From the results, it can be concluded that the combining site of th
is agglutinin should be a cavity type, and that a hydrophobic interaction i
n the vicinity of the binding site for sugar accommodation increases the af
finity. The binding site of CG-16 is as large as a tetrasaccharide of the b
eta -anomer of Gal, and is most complementary to lacto-N-tetraose and Gal(b
eta1-4)GlcNAc related sequences.