| Wheat germ agglutinin (WGA) (MW 36 kDa) is a dimeric, carbohydrate-free protein composed of two identical subunits. The amino acid sequence provides a figure of 21,600, based on 171 amino acids per polypeptide chain. The protein dissociates into monomers in acidic media, pK of the reaction 4. The receptor sugar for WGA is N-acetyl glucosamine (GlcNAc), GlcNacbeta14GlcNAc. These structures are present in many serum and membrane glycoproteins, bacterial cell wall peptidoglycans, chitin, cartilage glycosaminogyycons and glycolipids. Native WGA also react with glycoproteins with sialic acid residue. This lectin is useful for the purification of insulin receptors, serum proteins and neuronal tracing. The carbohydrate-binding specificity of WGA has been studied by variety of techniques, such as hapten inhibition of hemagglutination and specific precipitation of glycoconjugate, changes in fluorescence of the lectin (intrinsic) or of chromatogenic ligands (extrinsic), equilibrium dialysis, NMR and x-ray diffraction. |
