It is tetrameric globulin with molecular weight 102,000. Each subunit contains 237 amino acid residues, with a molecular weight of 25,500, which binds a Ca2+ and a Mn2+ and contains a sugar binding site. It can specifically bind to α-mannose and α-glucose (on cell membrane glycoprotein), and the binding site requires that the C-3/C-4 and C-6 unsubstituted hydroxyl groups in the six-membered ring of α-D- glucopyranose have the greatest affinity with mannose and mannose trisaccharide linked by α- 1 2 glycosidic bond.