Wheat germ agglutinin
Wheat germ agglutinin is a lectin that protects wheat from insects, yeast and bacteria. An agglutinin protein, it binds to N-acetyl-D-glucosamine and sialic acid. WGA has also been shown to interact with sialic acid residues on oligosaccharides. Succinylated WGA is selective for β-N-acetylglucosamine, making it a useful tool for detecting O-GlcNAc. WGA is composed of a mixture of three isoforms, which are quite similar to each other and each contain an unusually high amount of glycine. These three isoforms vary at a total of 10 amino acid positions and all have dimeric structures with four domains per monomer. Each domain is hevein-like and is stabilized by a disulfide bond. N-acetyl-D-glucosamine in the natural environment of wheat is found in the chitin of insects, and the cell membrane of yeast & bacteria. WGA is found abundantly—but not exclusively—in the wheat kernel, where it got the 'germ' name from. In mammals the N-acetyl-D-glucosamine that WGA binds to is found in cartilage and cornea among other places. In those animals sialic acid is found in mucous membranes, e.g. the lining of the inner nose, and digestive tract.
In solution, WGA exists mostly as a heterodimer of 38,000 daltons. It is cationic at physiological pH. It contains a Carbohydrate-binding module called CBM18.