Structure−Function Relationships of Soybean Proglycinins at Subunit Levels

Abstract

Glycinin consists of five kinds of subunits, group I (A1aB1b, A1bB2, and A2B1a) and group II (A3B4 and A5A4B3). cDNAs for individual subunits were cloned by reverse transcription-polymerase chain reaction method and expressed in Escherichia coli using pET vector. The recombinant proglycinins were purified by ammonium sulfate fractionation and column chromatography in the form of homotrimers. Physicochemical properties such as molecular dimensions, solubility, surface hydrophobicity, thermal stability, and emulsifying ability of individual proglycinins were studied. Molecular dimensions were proportional to molecular size for all proglycinins except A2B1a. Solubility was intrinsic to each proglycinin. At the ionic strength of 0.5, all proglycinins except A1aB1b showed a very low solubility at acidic pH, but A1aB1b was soluble to higher than 60%. At ionic strength 0.08, all proglycinins exhibited isoelectric precipitation, although A2B1a and A1bB2 were not completely insoluble. The order of emulsifying ability (A1bB2 < A2B1a < A5A4B3 < A3B4 < or = A1aB1b) was not of the same for surface hydrophobicity (A5A4B3 < A1aB1b < or = A3B4 < A1bB2 < A2B1a) and thermal stability (A1bB2 << A2B1a < or = A5A4B3 < A3B4 < or = A1aB1b).

Proteomic and genetic analysis of glycinin subunits of sixteen soybean genotypes

“…The third exon of Gy4 contains the most hypervariable region (HVR) of group II subunits [25]. Subunits within the same group showed high identity (higher than 90%) whereas subunits between groups showed low identity (less than 60%) [27].…”

“…The subunit pairings of glycinin molecules are a heterogeneous complex of A1aBx, A1aB1b, A2B1a, A3B4 and A5A4B3, which are covalently linked by disulfide bonds except for the A4 subunit present in the G4 subunit [19,33]. For each subunit there is more than 84% homology within the group and 45e49% between groups [27].…”

Vacuolar Sorting Behaviors of 11S Globulins in Plant Cells

“…3,17,18) Pumpkin pro11S had a higher hydrophobicity than pea pro11S or proA1aB1b (Fig. 8), suggesting that it is more prone to form aggregates than the other two.…”

“…A1aB1b and A2B1a are the most hydrophilic and hydrophobic respectively among soybean 11S group I subunits. 17) Immunologic analysis was performed to compare the accumulation levels of the 11S in transgenic BY-2 cells (Fig. 7).…”

“…18) Prak et al analyzed the physicochemical properties of five subunits of soybean pro11S, 17) and reported that the surface hydrophobicity of proA2B1a was much higher than those of the other four subunits. Since the surface hydrophobicity of proteins might influence their aggregation, we compared the surface hydrophobicity of proA1aB1b, proA2B1a, pumpkin pro11S, and pea pro11S by protein fractionation using ammonium sulfate (Fig.…”