Plant seed storage proteins, whose principal function appears to be the majornitrogen source for the developing plant, can be classified, on the basis oftheir structure, into different families. 11-S are non-glycosylated proteinswhich form hexameric structures [<cite idref="PUB00001358"/>, <cite idref="PUB00004572"/>]. Each of the subunits in the hexamer isitself composed of an acidic and a basic chain derived from a single precursorand linked by a disulphide bond. This structure is shown in the followingrepresentation.<pre> +-------------------------+ | | xxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxNGxCxxxxxxxxxxxxxxxxxxxxxxx |------Acidic-subunit-------------||-----Basic-subunit------| |-----------------About-480-to-500-residues-----------------|'C': conserved cysteine involved in a disulphide bond.</pre>Members of the 11-S family include pea and broad bean legumins, oil seed rapecruciferin, rice glutelins, cotton beta-globulins, soybean glycinins, pumpkin11-S globulin, oat globulin, sunflower helianthinin G3, etc.This family represents the precursor protein which is cleaved into the two chains. These proteins contain two beta-barrel domains.This family is a member of the 'cupin' superfamily on thebasis of their conserved barrel domain ('cupa' is the Latin termfor a small barrel).