Multi-antennary Galβ1 → 4GlcNAc and Galβ1 → 3GalNAc clusters as important ligands for a lectin isolated from the sponge Geodia cydonium

The affinity of a lectin from the sponge Geodia cydonium (GCL-I) for multi-antennary Galβ1 → 4GlcNAc and Galβ1 → 3GalNAc ligands was studied by both the biotin/avidin-based microtiter plate lectin binding assay and the inhibition of lectin-glycoform interaction. Among the glycoforms tested for binding, GCL-I reacted strongly with three multi-antennary Galβ1 → 4GlcNAc clusters containing glycoproteins (asialo human and bovine α₁-acid gps and asialo fetuin), T (Galβ1 → 3GalNAc) rich glycoprotein from porcine salivary gland, asialo bird nest gp, and human blood group A active cyst gp, while human and bovine α₁-acid gps, fetuin, and Tn containing gps were inactive. Among the haptens tested for inhibition, tri-antennary Galβ1 → 4GlcNAc (Tri-II) was about 1500, 72, and 72 times more active than GalNAc, Galβ1 → 4GlcNAc (II), and Galβ1 → 3GalNAc (T), respectively. Based on the present and previous results, it is proposed that tri-antennary Galβ1 → 4GlcNAc and Galβ1 → 3GalNAc clusters, in addition to GalNAcα1 → 3GalNAc and GalNAcα1 → 3Gal, are also important ligands for binding; and sialic acid of glycoprotein does interfere with binding.