Structure−Physicochemical Function Relationships of Soybean β-Conglycinin Constituent Subunits

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Abstract
β-Conglycinin, one of the dominant storage proteins of soybean, has a trimeric structure, being composed of three subunits α, α‘, and β. The α and α‘ subunits contain the extension regions in addition to the core regions common to all subunits, which are N-glycosylated. Physicochemical functions of recombinant nonglycosylated individual subunits and deletion mutants (αc and α‘c) lacking the extension regions of the α and α‘ subunits were examined at pH 7.6 and 3.7 at low (μ = 0.08) and high (μ = 0.5) ionic strengths. Although individual recombinant subunits exhibited different properties at all conditions, there were some consistencies. Surface hydrophobicities and thermal stabilities of the individual subunits were likely to be conferred by their core regions, and the carbohydrate moieties did not contribute to these properties at any conditions examined here. Solubility at μ = 0.08, heat-induced association, and emulsifying ability remarkably depended on the extension regions and the carbohydrate moieties in addition to the structural features of the core regions. These findings indicate that various end products could be produced by the selection of soybean varieties containing β-conglycinin with different subunit compositions and suggest a direction for a principle of soybean breeding. Keywords: β-Conglycinin; structure−physicochemical function relationship; physicochemical functions; soybean; Glycine max L.