Psophocarpus tetragonolobus lectin (PTL, psophocarpin B1, a storage protein with chymotrypsin inhibitory activity), is isolated from winged bean seeds and purified by affinity chromatography. The seed contains two lectins in which PTL I is the basic and PTL II is the acidic of the two.
PTL is a dimeric glycoprotein with specificity to GalNAc, with eluting sugar GalNAc. This lectin agglutinates trypsinized rabbit and human erythrocytes (types A,B, and O). PTL I recognizes blood group A-substance derived oligosaccharides such as trisaccharide GalNAc?1-3Gal?1-4Glc. Nonpolar interactions play an important role in stabilization of the lectin-sugar complex. Projection of α1,3 linked Gal/GalNAc leads to steric hindrance and prevents the binding of blood group A and B reactive sugars. The unique specificity of PTL II makes it to be useful in isolation and characterization of terminally monofucosylated H-reactive oligosaccharides from those that are difucosylated or internally fucosylated.