Oxidative protein folding: Selective pressure for prolamin evolution in rice

During seed development, endosperm cells of highly productive cereals, including rice, synthesize disulfide-rich proteins in large amounts and deposit them into storage organelles. Disulfide bond formation involves electron transfer and generates H₂O₂ as a by-product. To ensure proper development and maturation of seeds, the endosperm cells must supply large amounts of oxidizing equivalents to dithiols in nascent proteins in a controlled manner. This review compares multiple oxidative protein folding systems in yeast, cultured human cells, and rice endosperm. We discuss possible roles of ERO1, other sulfhydryl oxidases, and the protein disulfide isomerase family in the formation of disulfide bonds in storage proteins and the development of protein bodies. Rice prolamins, encoded by a multigene family, are divided into Cys-rich and Cys-depleted subgroups. We discuss the potential importance of disulfide bond formation in the evolution of the prolamin family in japonica rice.