Wheat Germ Agglutinin

TLDR

Crystalline wheat germ agglutinin was isolated from unprocessed wheat germ using a novel purification method and characterized for purity and molecular properties. The purified agglutinin has a monomeric molecular weight of ~17 kDa (2.1 S), dimerizes at neutral pH to ~35 kDa (3.6 S), contains two high‑affinity N‑acetylglucosamine binding sites (Kd ≈ 7.6 × 10⁻⁴ M), and β‑1,4 di‑ and trisaccharides bind with Kd values of 4.9 × 10⁻⁶ M and 1.2 × 10⁻⁵ M, respectively.

Abstract

Abstract Crystalline wheat germ agglutinin was prepared from unprocessed wheat germ by a new purification procedure. Its purity and some of its molecular characteristics were examined by a number of criteria. Sedimentation analysis gave a molecular weight of 17,000 ± 1,000 and a sedimentation coefficient of 2.1 S when determined in 0.05 n HCl. At neutral pH, the agglutinin dimerizes with a molecular weight of around 35,000 and a sedimentation coefficient of 3.6 S. Amino acid analyses indicate that the protein contains a high amount of glycine and half-cystine; none of the latter is present as cysteine. Three times crystallized agglutinin is devoid of neutral sugars. Equilibrium dialysis experiments using N-acetyl-[1-14C]glucosamine indicate that the agglutinin has 2-binding sites for N-acetylglucosamine per mole of the polypeptide chain with a dissociation constant of 7.6 x 10-4 m. This binding is highly specific. The β-1,4 di- and trisaccharides of N-acetylglucosamine showed higher affinities with apparent dissociation constants of 4.9 and 1.2 x 10-5 m, respectively.