Pea legumin overexpressed in wheat endosperm assembles into an ordered paracrystalline matrix

Legumin, a major component of pea seed storage vacuoles, is synthesized by a number of paralogous genes. The polypeptides are cleaved posttranslationa lly and can form mixed hexamers. This heterogeneity hampers structural stud ies, based on the production of hexamer crystals in vitro. To study a singl e type of homogenous legumin we produced pea legumin A in transgenic wheat (Triticum aestivum) endosperm where prolamins are predominant and only smal l amounts of globulins accumulate in separate inclusions. We demonstrated t hat the legumin precursor was cleaved posttranslationally and we confirmed assembly into 11S hexamers. Legumin was deposited within specific regions o f the inclusion bodies. Angular legumin crystals extended from the inclusio n bodies into the vacuole, correlating with the high legumin content. This suggests that the high-level production of a single type of legumin polypep tide resulted in the spontaneous formation of crystals in vivo. The use of a heterologous cereal system such as wheat endosperm to produce, isolate, a nd recrystallize homogenous 11S legume globulins offers exciting possibilit ies for structural analysis and characterization of these important seed st orage proteins.