Gluten genes

Figure 6.1. The role of HMW subunits in gluten structure and functionality. Amino acid sequences derived from direct analysis of purified proteins and the isolation and sequencing of corresponding genes show that the proteins have highly conserved structures, with repetitive domains flanked by shorter nonrepetitive domains containing cysteine residues (SH) available for formation of interchain disulphide bonds. Molecular modelling indicates that the individual repetitive domains form a loose spiral structure (bottom right) while SPM shows that they interact by noncovalent forces to form fibrils (centre right). Includes figures from Parchment et al. (2001) and Humphries et al. (2000).

Because of their functional importance, the gluten proteins have been studied in detail using genetical, molecular, biochemical, and biophysical approaches. This has revealed details of the numbers and locations of their controlling genes loci, their amino acid sequences, their conformations, and their relationship to various functional properties [39]. 

Little was known about the structure of these proteins until 20 years ago. Then, boosted by new technology developments such as molecular cloning, it became possible to isolate cloned cDNA and genes for all the major groups of gluten... 

In case of bread wheat, increases in gluten elasticity could be obtained by inserting additional genes for HMW-GS to increase the total amount of HMW subunit protein. In addition, these genes could possibly be mutated to give more subtle differences, due to effects on the cross-linking or other properties of the glutenin polymers. 

Also they differ in amino acid composition from the gluten proteins, possessing lower amounts of glutamic acid and more lysine. Unfortunately, because they are present in the wheat endosperm in minor proportions, their presence it is not enough to overcome the lack of lysine in wheat. Analysis of aneuploid stocks of the wheat variety Chinese Spring has revealed that the HMW albumins of 69,63,60, and 45 kDa are controlled by genes on the chromosome arms 4DL, 4AL, SAL and SDL respectively. 

O. D. Anderson, B. Cassidy, J. Steffen, J. Dvorak, and F.C. Greene, 1991. Structure of the high-and low- molecular-weight gene families of the homoeologous group 1 chromosomes of the hexaploid bread wheat cultivar Cheyenne, pp. 512-519 in Gluten Proteins 1990. W. Bushuk and R. Tkachuk, eds. Am. Assoc. Cereal Chem. St. Paul, MN. 

Fewer than 10 copies of the gluten detection gene 1.56 ppm gliadin... 

Figure 11.4 Schematic representation of the chromosomal location of genes coding for the gluten proteins. Glutenin polymerizes by a post-translational process to form the large glutenin polymers. (MacRitchie, F. 1999. Cereal Foods World 44 188-193.)...

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