PURIFICATION AND CHARACTERIZATION OF N-GLYCOLYLNEURAMINIC-ACID-SPECIFIC LECTIN FROM SCYLLA-SERRATA

A sialic-acid-binding lectin with specificity for N-glycolylneuraminic acid (NeuGc) was purified from the hemolymph of the marine crab Scyll a serrata by affinity chromatography using thyroglobulin-coupled agaro se. The binding specificity of Scylla lectin distinguishes it from oth er known sialic-acid-specific lectins found in Limulus polyphemus and Limax flavus, which show a broader range of specificity for sialic aci ds. The molecular mass of the purified lectin is about 55 kDa. Under r educing conditions (SDS/PAGE), it resolved into two subunits of 30 kDa and 25 kDa. NeuGc inhibited hemagglutination activity of the purified lectin at a concentration as low as 0.6 mM, whereas N-acetylneuramini c acid (NeuAc) even at a concentration of 100 mM, failed to inhibit he magglutination. This finding was supported by potent inhibition of hem agglutination by bovine and porcine thyroglobulins, which contain a Ne uGcalpha2-6Gal as terminal component of oligosaccharide residues. Neit her glycoproteins (glycophorin NN; porcine submaxillary mucin), which contain NeuAcalpha2-3Gal/GalNAc and NeuAcalpha2-6GalNAc, nor human aci d glycoprotein, which contains NeuAcalpha2-3/alpha2-6 Gal, or colomini c acid, a sialopolymer with NeuAcalpha2-8NeuAc, inhibited the lectin a ctivity. The specificity of the lectin for NeuGc appears to account fo r the fact that it agglutinates rabbit and mice erythrocytes, but not human A, O, AB, rat or chicken erythrocytes, which contain NeuAc. The inability of the lectin to agglutinate erythrocytes (horse) that promi nently express NeuGc could be due to O-acetylation of NeuGc. In suppor t of this, bovine submaxillary mucin, which contains O-acetylated NeuG c inhibited the hemagglutination of the lectin better after removal of O-acetyl groups by base treatment. The unique specificity of Scylla l ectin is of diagnostic potential for human cancer tissues expressing N euGc, since NeuGc is not found in normal human tissues.