E.V. Metakovsky, Calle Montera, 42, Piso 6, Madrid 28013 Spain; R.A. Graybosch, USDA-ARS, University of Nebraska, Lincoln, NE 68583, USA
Gliadin and Glutenin: The Unique Balance of Wheat Quality
Pages 85-114
DOI: https://doi.org/10.1094/9781891127519.005
ISBN: 978-1-891127-51-9
Abstract
Gliadin is the most abundant storage protein of the wheat seed, amounting to about 40%, by weight, of wheat-flour protein. It comprises a considerable part of the final mass of many wheat-based food products, and it is one of the major protein components of the human diet of many societies. For a wheat plant, it serves only as a reserve protein synthesized in developing wheat grain (Mecham et al 1981; Green 1983) and is used by a germinating grain as a source of amino acids (Konzak 1977; Kasarda 1989).
The molecular mass of gliadin polypeptides ranges from 15 to 60 kDa, but most are in the narrow range 25–40 kDa. Gliadin molecules are not glycosylated and their molecular mass can be estimated rather precisely by means of simple SDS-electrophoretic procedures (Bunce et al 1985). Gliadin polypeptides have a low content of charged amino acids and form only intra-molecular disulfide bonds. They are, therefore, assumed to exist as monomeric molecules (reviewed in Kasarda 1989; Shewry and Tatham 1990; Tatham and Shewry 1995) with a specific three-dimensional structure (Müller and Wieser 1995, 1997).
Analysis of many gliadin-coding genes shows that they are all intron-free, consist of several domains, and have rather ordinary promoter and other flanking sequences (Rafalski et al 1984; Sumner-Smith et al 1985; Rafalski 1986; Anderson et al 1997). An important characteristic of all gliadin genes is the presence in their structure of long domains of repeated sequences of different length and nucleotide composition. Gliadin genes (and therefore derived gliadin polypeptides) may be grouped into several families on the basis of their encoded amino-acid sequences and details of domain structure (reviewed in Shewry and Tatham 1990; Sabelli and Shewry 1991; Tatham and Shewry 1995). The differences between gliadin genes belonging to the same family often are found to be single-nucleotide substitutions, small deletions/insertions and the number of repeats in corresponding domains (Kasarda et al 1984; Okita et al 1985; Sumner-Smith et al 1985; Scheets and Hedgcoth 1988).
