Formation of Amyloid Fibrils from Kidney Bean 7S Globulin (Phaseolin) at pH 2.0

Abstract

The amyloid fibrils formed by heating 1.0% (w/v) kidney bean phaseolin (7S globulin) solution at pH 2.0 with an ionic strength of 20 mM at 85 degrees C were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), binding of thioflavin T (Th T) and Congo Red dyes, and circular dichroism spectroscopy. The morphology of the formed fibrils was closely dependent upon heating time from 15 to 720 min. The diameters of the fibrils formed at various times were similar, but the mean contour length progressively increased with heating time. The Th T maximum fluorescence also progressively increased with heating time. The heating process caused remarkable changes in secondary, tertiary, and quaternary conformations of the phaseolin, but the extents of the changes were closely related to the heating time. With a short heating time (e.g., 15 min), the beta-strand content decreased from 38.7 to 22.9%, but further heating resulted in recovery of beta-strand structure. The tertiary and quaternary conformations gradually became flexible and unfolded upon heating. Gel electrophoresis analysis indicated that heating disrupted the polypeptides of phaseolin, leading to the formation of fragments with lower molecular mass (e.g., <10 kDa after 360 min). The results suggest that the amyloid fibril formation of phaseolin (7S globulin) involved the disruption of its polypeptides, as well as conformational changes at secondary, tertiary, and quaternary structural levels. This appears to be the first direct observation of amyloid fibrils from legume 7S storage globulin.

Effect of heat-induced formation of rice bran protein fibrils on morphological structure and physicochemical properties in solutions and gels

“…Secondary structural compositions generally have dichroic activities in a wavelength range of 190 to 250 nm (25). The secondary structural compositions (including α-helix, β-strand, turns, and random coils) of RBP samples were calculated using the CONTIN/LL program in CD Pro software (16). At pH 2.0, the fibrils had 7.9% α-helix, 33.2% β-strand, 22.5% turns, and 36.5% random coil.…”

Evaluation of protease resistance and toxicity of amyloid-like food fibrils from whey, soy, kidney bean, and egg white

“…OVA was purified from day-fresh chicken egg white using DEAE (2-(diethylamino)ethyl) Sephacel anion exchange resin (De Groot & de Jongh, 2003) with stepwise elution of increasing NaCl concentration (20-200 mM), dialysis against distilled water, and 0.22 lm sterile filtration. SPI and KPI were prepared from freshly ground soy bean and kidney bean flour using slightly modified extraction methods (Akkermans et al, 2007;Tang, Zhang, Wen, & Huang, 2010). Briefly, fresh bean flour was stirred in extraction buffer for 45 min (SPI extraction buffer: 30 mM Tris, 10 mM b-mercaptoethanol, pH 8; KPI extraction buffer: 0.5 M NaCl, 25 mM HCl, pH 1.6).…”

Improvement of heat-induced fibril assembly of soy β-conglycinin (7S Globulins) at pH 2.0 through electrostatic screening

“…β-LG; Arnaudov, de Vries, Ippel, & van Mierlo, 2003;Gosal et al, 2004;Arnaudov & de Vries, 2006;Bolder, Vasbinder, Sagis, & van der Linden, 2007;Akkermans et al, 2008;Oboroceanu, Wang, Brodkorb, Magner, & Auty, 2010), BSA (Veerman, Sagis, Heck, & van der Linden, 2003;Vetri et al, 2011), lysozyme (Misha et al, 2007), and legume proteins (i.e. 7S or 11S globulins from soy and kidney beans; Akkermans et al, 2007;Tang & Wang, 2010;Tang, Zhang, Wen, & Huang, 2010). Among those fibril-forming proteins, β-LG is one of the most investigated food proteins.…”