Capillary electrophoresis for analysis of microheterogeneous glutelin subunits in rice (Oryza sativa L.).

Glutelin, the major storage protein of rice seed, consists of microheterogenous subunits and partially exists in a macromolecular form that is polymerized by intersubunit disulfide bonds. In order to analyze the glutelin subunits using high-throughput CE, we first identified a sample preparation procedure suitable for CE. The polymerized glutelin treated with a reductant could not dissociate into its constituent monomer subunits when it was dissolved in an acidic solution. However, the glutelin dissociated into its subunits and component α and β polypeptides when it was denatured and reduced by an appropriate amount of urea and 2-mercaptoethanol at a specific incubation time and temperature. The molecular species of the completely dissociated α and β polypeptides were identified and quantitatively analyzed by CE using glutelin mutants. The CE analysis also demonstrated that the actual subunit variation in terms of the charge and/or size of the β polypeptides is much smaller than predicted when compared with that of α polypeptides, even under denaturing and reducing condition. Thus, the combined analytical system described here will be useful for basic and applied research, such as the kinetic characterization of higher-order structure and the quantitative evaluation of glutelin in a large number of diverse rice varieties.