Allergens of the cupin superfamily

The cupin family comprises a family of proteins possessing a common β-barrel structure that is thought to have originated in a prokaryotic ancestor. This structural motif is found as a single domain in fungal spherulins, fern sporulins and the germins/oxalate oxidase proteins of plants, while the globular storage proteins of plants, called legumins (11 S) and euvicilins (7 S), are two-domain cupins. The 11 S globulins are hexameric heteroligomeric proteins of Mr ~ 360000, with each subunit comprising an acidic 30000–40000-Mr polypeptide that is disulphide-linked to a 20000-Mr basic polypeptide. A number of cupins have been identified as major plant food allergens, including the 7 S globulins of soybean (β-conglycinin), peanut (conarachin; Ara h 1), walnut (Jug r 2) and lentil, and the 11 S globulins of peanut (arachin; Ara h 3), soybean (glycinin) and possibly also coconut and walnut. Other members of the cupin superfamily have not been identified as allergens, with the exception of one germin (germination-specific protein) from pepper. Cupins are generally very stable proteins. A summary of our current knowledge of allergenic seed storage globulins will be presented, together with an overview of cupin structure and stability properties, as illustrated by the allergenic soya globulins, glycinin and β-conglycinin.