Gliadins from wheat grain: an overview, from primary structure to nanostructures of aggregates
Gliadins are well-known wheat grain proteins, particularly important in food science. They were studied as early as the 1700s. Despite their long history, it has been difficult to identify their higher-order structure as they aggregate in aqueous solution. Consequently, most studies have been performed by extracting the proteins in 70% ethanol or dilute acidic solutions. The carboxy-terminal half of α- and γ-gliadins have α-helix-rich secondary structures stabilized with intramolecular disulfide bonds, which are present in either aqueous ethanol or pure water. The amino-terminal-repeat region of α- and γ-gliadins has poly-L-proline II and β-reverse-turn structures. ω-Gliadins also have poly-L-proline II and β-reverse-turn structures, but no α-helix structure. The size and shape of gliadin molecules have been determined by assessing a variety of parameters: their sedimentation velocity in the analytical ultracentrifuge, intrinsic viscosity, small-angle X-ray scattering profile, and images of the proteins from scanning probe microscopes such as a tunneling electron microscope and atomic force microscope. Models for gliadins are either rods or prolate ellipsoids whether in aqueous ethanol, dilute acid, or pure water. Recently, gliadins have been shown to be soluble in pure water, and a novel extraction method into pure water has been established. This has made it possible to analyze gliadins in pure water at neutral pH, and permitted the characterization of hydrated gliadins. They formed hierarchical nanoscale structures with internal density fluctuations at high protein concentrations.
KeywordsGliadin Wheat protein Protein aggregate SAXS Nanostructure
This work was supported by JSPS KAKENHI Grant Number 26660111 to R.U, JP15H02042 to M.S. and a grant from the Tojuro Iijima Foundation for Food Science and Technology.
Compliance with ethical standards
Conflict of interest
Reiko Urade declares that she has no conflicts of interest. Nobuhiro Sato declares that he has no conflicts of interest. Masaaki Sugiyama declares that he has no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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