The effect of the N-linked glycans on structural features and physicochemical functions of soybean β-conglycinin homotrimers

beta-Conglycinin is a trimeric protein consisting of three subunits, alpha, alpha', and beta, which are N-glycosylated. The alpha and alpha' subunits contain extension regions in addition to core regions common to all subunits. We purified homogeneous trimers consisting of only alpha, alpha', or beta from mutant soybean cultivars containing beta-conglycinin lacking one or two subunits: alpha homotrimers from an alpha'-Iacking mutant, alpha' homotrimers from an alpha-lacking mutant, and beta homotrimers from an alpha- and alpha'-Iacking mutant. Structural features and physicochemical functions of the three homotrimers were examined and compared with those of recombinant homotrimers having no N-linked glycans. The native homotrimers have secondary structures very similar to those of the recombinant ones. In analogy with the recombinant homotrimers, the native ones exhibit different thermal stabilities from one another (beta > alpha' > alpha), and the native alpha and alpha' homotrimers exhibit better solubility, emulsifying ability, and heat-induced association than the native beta homotrimer. Further, the N-linked glycans contribute to solubilities of the three subunits at low ionic strength (mu = 0.08) and to the emulsifying ability of the native beta homotrimer. N-Linked glycans also prevent heat-induced associations of the native alpha and alpha' homotrimers but do not contribute to the secondary structure and the thermal stability of beta-conglycinin.