Accumulation of storage proteins in plant seeds is mediated by amyloid formation.

Amyloids are protein aggregates with a highly ordered spatial structure giving them unique physicochemical properties. Different amyloids not only participate in the development of numerous incurable diseases but control vital functions in archaea, bacteria and eukarya. Plants are a poorly studied systematic group in the field of amyloid biology. Amyloid properties have not yet been demonstrated for plant proteins under native conditions in vivo. Here we show that seeds of garden pea Pisum sativum L. contain amyloid-like aggregates of storage proteins, the most abundant one, 7S globulin Vicilin, forms bona fide amyloids in vivo and in vitro. Full-length Vicilin contains 2 evolutionary conserved ß-barrel domains, Cupin-1.1 and Cupin-1.2, that self-assemble in vitro into amyloid fibrils with similar physicochemical properties. However, Cupin-1.2 fibrils unlike Cupin-1.1 can seed Vicilin fibrillation. In vivo, Vicilin forms amyloids in the cotyledon cells that bind amyloid-specific dyes and possess resistance to detergents and proteases. The Vicilin amyloid accumulation increases during seed maturation and wanes at germination. Amyloids of Vicilin resist digestion by gastrointestinal enzymes, persist in canned peas, and exhibit toxicity for yeast and mammalian cells. Our finding for the first time reveals involvement of amyloid formation in the accumulation of storage proteins in plant seeds.

Lupinus albus γ-Conglutin, a Protein Structurally Related to GH12 Xyloglucan-Specific Endo-Glucanase Inhibitor Proteins (XEGIPs), Shows Inhibitory Activity against GH2 ß-Mannosidase.

γ-conglutin (γC) is a major protein of Lupinus albus seeds, but its function is still unknown. It shares high structural similarity with xyloglucan-specific endo-glucanase inhibitor proteins (XEGIPs) and, to a lesser extent, with Triticum aestivum endoxylanase inhibitors (TAXI-I), active against fungal glycoside hydrolases GH12 and GH11, respectively. However, γC lacks both these inhibitory activities. Since ß-galactomannans are major components of the cell walls of endosperm in several legume plants, we tested the inhibitory activity of γC against a GH2 ß-mannosidase (EC 3.2.1.25). γC was actually able to inhibit the enzyme, and this effect was enhanced by the presence of zinc ions. The stoichiometry of the γC/enzyme interaction was 1:1, and the calculated Ki was 1.55 µM. To obtain further insights into the interaction between γC and ß-mannosidase, an in silico structural bioinformatic approach was followed, including some docking analyses. By and large, this work describes experimental findings that highlight new scenarios for understanding the natural role of γC. Although structural predictions can leave space for speculative interpretations, the full complexity of the data reported in this work allows one to hypothesize mechanisms of action for the basis of inhibition. At least two mechanisms seem plausible, both involving lupin-γC-peculiar structures.

Effect of peanut protein isolate on functional properties of chicken salt-soluble proteins from breast and thigh muscles during heat-induced gelation.

In this study, we investigated the impact of peanut protein isolate (PPI) on the functional properties of chicken salt-soluble protein (SSP) prepared from breast and thigh muscles during heat-induced gelation. The addition of PPI increased the water-holding capacity, gel strength and elasticity of heat-induced chicken SSP mixed gel. Breast and thigh SSP had the best gel properties at the addition of 2.5% and 3.5% PPI, respectively. Rheology indicated that thigh SSP showed higher storage modulus (G') than breast SSP. Differential scanning calorimetry showed that the addition of PPI changed transition temperatures (Tmax) and enthalpy of denaturation (ΔH) of chicken SSP. Scanning electron microscopy indicated that the PPI-treated SSP gels had more compact ultrastructures than controls. The results suggested that PPI may be a potential protein additive for improve the characteristics of SSP gelations.

Physicochemical properties of ß and α'α subunits isolated from soybean ß-conglycinin.

Soy protein has shown great potential for use in biobased adhesives. ß-Conglycinin is a major component of soy protein; it accounts for 30% of the total storage protein in soybean seeds. ß-Conglycinin was isolated and purified, and its subunits' (ß, α'α) physicochemical and adhesive properties were characterized. Crude ß-conglycinin was isolated from soy flour and then purified by the ammonium sulfate precipitation method. The α'α and ß subunits were isolated from the purified ß-conglycinin by anion exchange chromatography. Yields of α'α subunits and ß subunits from 140 g of soy flour were 1.86 g (1.3%) and 0.95 g (0.67%), respectively. The minimum solubility for α'α subunits, ß subunits, and ß-conglycinin occurred in pH ranges of 4.1-5.4, 3.5-7.0, and 4.8-5.3, respectively. Transmission electron microscopy showed that the ß subunits existed as spherical hydrophobic clusters, whereas α'α subunits existed as uniformly discrete particles at pH 5.0. Differential scanning calorimetry showed that ß subunits had higher thermal stability than α'α subunits. The pH had a lesser effect on adhesion strength of the ß subunits than on that of the α'α subunits. The adhesives made from ß subunits also showed greater water resistance than those from α'α subunits and ß-conglycinin. Soy protein rich in ß subunits is likely a good candidate for developing water-resistant adhesives.