Cereal proteins constitute about 10% of the grain dry weight and are an important source of protein in the diet. According to solubility, they are divided into albumins and globulins soluble in saline, prolamins soluble in ethanol, and glutelins soluble in propanol/urea/dithioerythritol.
Prolamins
Prolamins are plant storage proteins rich in proline amino acids. They are poorly soluble in water and most soluble in 70%-80% alcohols, weak acids, and alkaline solutions. Prolamins are found mainly in the seeds of cereal grains such as wheat (gliadin), barley (hordein), rye (secalin), corn (zein), sorghum (kafirin), and oats (avenin).
Glutelins
Glutelins are a class of prolamin proteins in the endosperm of certain seeds of the grass family, such as glutenin in wheat, hordenin in barley, zeanin in corn, and oryzenin in rice. They are soluble in very dilute acids and alkalis, insoluble in neutral solvents. Glutenins and gliadins constitute the gluten proteins, which are stored in endosperm of the seed along with starch. Both glutenins and gliadins have certain amino acid sequences that act as antigenic epitopes for celiac disease.
Recombinant Gliadin Peptides
Gliadin is the main component of wheat gluten, which is composed of single-chain polypeptides with average molecular weight of 25–100 kDa linked by intramolecular disulfide bonds. Gliadin can be extracted from gluten with 70% ethanol and has remarkably low solubility in aqueous solution except at extreme pH. Its low water solubility is attributed to the presence of disulfide bonds and synergistic hydrophobic interactions. Gliadin contains equal amounts of polar and neutral amino acids, mainly glutamine (about 40%) and a high content of proline (14%).
Gliadin peptides are the main immunotoxic antigens in celiac disease. They are substrates for tissue transglutaminase (TG2), which specifically deamidates glutamine residues within these peptides, thereby greatly enhancing their immunogenicity. Amerigo Scientific offers a set of fusion proteins with different native and deamidated peptide sequences that facilitate the analysis of antibodies found in samples associated with celiac disease.
Albumins and Globulins
The albumins and globulins are rich in lysine and valine. Albumins are soluble in water and are usually low in non-essential amino acid glycine. Albumins are found in plants and animals, including egg albumin, myogenin in muscle, lactalbumin in milk, legumelin in peas, leucosin in wheat, etc.
Globulins are a family of globular proteins with higher molecular weights than albumins, insoluble in pure water, but soluble in dilute salt solutions. Globulins are widely distributed in animals and higher plants and are the main storage proteins in legumes, such as ovo-globulin in egg yolk, myosin in muscle, edestin in hemp seed, phaseolin in beans, legumin in peas, arachin in peanuts, amandin in almonds, and so on.
