A. Juhász, Agricultural Research Institute of the Hungarian Academy of Sciences, 2 Brunszvik, Martonvasar, H-2462, Hungary; M.C. Gianibelli, CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia
Gliadin and Glutenin: The Unique Balance of Wheat Quality
Pages 171-212
DOI: https://doi.org/10.1094/9781891127519.009
ISBN: 978-1-891127-51-9
Abstract
Wheat is unique because only wheat flour has the ability to form dough that exhibits the rheological properties required for the production of leavened bread, as well as a wide variety of other foods that have been developed to take advantage of these attributes. Its unique properties reside primarily in the gluten-forming storage proteins. Gluten proteins, gliadins and glutenins, are the reason wheat is the most important source of protein in the human diet. One of the aims of wheat breeding is improving protein quality (e.g., high dough strength and extensibility). Therefore, research has been conducted to assess the importance of glutenin subunits, with emphasis on high-molecular-weight glutenin subunits (HMW-GS) (Payne et al 1981, 1987; Branlard and Dardevet 1985; Gupta and MacRitchie 1994; Popineau et al 1994). The initial interest in the HMW-GS arose from their easy separation using SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Although the HMW-GS represent a small proportion of the total glutenin, they have been shown to be particularly important components of the gluten complex affecting dough properties (Shewry et al 1992, 1997). By contrast, low-molecular-weight glutenin subunits (LMW-GS), which are present in gluten at about three times the amount of the HMW-GS, have been difficult to separate because their complexity, heterogeneity and overlap with other polypeptides in SDS-PAGE analysis. Although the LMW-GS are also known to be essential contributors in determining dough properties (Gupta et al 1989, 1994), this group of proteins has not been studied in detail. The difficulties, which were principally due to overlaps between LMW-GS and gliadins, were largely resolved when Singh and Shepherd (1988) developed a simplified two-step SDS-PAGE method. Earlier, Jackson et al (1983), using a more complicated two-dimensional (2D) electrophoresis procedure, had improved resolution and began systematic work on this group of subunits. A combination of two different 2D techniques a) isoelectric focusing (IEF) and SDS-PAGE for separation of neutral and acid proteins, and b) non-equilibrium pH gradient electrophoresis (NEPHGE) and SDS-PAGE for separation of basic proteins was needed for a good resolution of the LMW-GS. More recently, Singh et al (1991) and Gupta and MacRitchie (1991) reported an improved 1D method to analyze polymeric proteins after prior extraction of monomeric proteins with either 50% propan-1-ol or dimethyl sulfoxide (DMSO), respectively.
Advances in the characterization of LMW-GS have been enhanced by the production of wheat-rye translocation lines (single, double and triple), in both bread and durum wheat, permitting the simplification of the electrophoretic pattern for closer study of the LMW-GS alleles (Gupta and Shepherd 1993). Reversed-phase high-performance liquid chromatography (RP-HPLC) has also proved useful for the study of LMW-GS, showing that these proteins have higher hydrophobic surfaces than those from HMW-GS and comparable to the hydrophobic surfaces of gliadins.
Recent improvements in capillary electrophoresis reported by Bean and Lookhart (2000) allowed clear characterization of all glutenin subunits. A proteomics approach has also been used for studying LMW-GS in wheat flour (Cunsolo et al 2004). Nowadays more simple and precise 2D gels can be run and a clear improvement has been reached in the identification of individual spots of LMW-GS compared with those obtained in the early eighties (Jackson et al 1983). In addition, the analysis of their gene sequences, reported in the databases, and the study of their deduced protein sequences brought a large amount of information and knowledge of this type of proteins. A review of different aspects of LMW-GS genes and their deduced proteins is compiled in this chapter with emphasis on their role on dough properties.
