Improving wheat to remove coeliac epitopes but retain functionality

Improving wheat to remove coeliac epitopes but retain functionality

Shewry and Tatham 2016

Coeliac disease is an intolerance triggered by the ingestion of wheat gluten proteins. It is of increasing concern to consumers and health professionals as its incidence appears to be increasing. The amino acid sequences in gluten proteins that are responsible for triggering responses in sensitive individuals have been identified. The majority of coeliac toxic peptides have been identified from in vitro studies using peptides cultured with T cell lines or T cell clones derived from the biopsied small intestinal mucosa of CD patients. One of the mostimmunodominant sequence is the 33-residue peptide from α-gliadin that contains the overlapping T-cell epitopes DQ2.5-glia-α1a, b and DQ2.5-glia-α2. This “33-mer” is resistant to gastrointestinal digestion (with pepsin and trypsin) and was initially identified as the major coeliac toxic peptide in the gliadins. Moreover, there is a marked difference in the distributions of epitopes among and between different groups of gluten proteins. The most coeliacactive T-cell epitopes are present on the α-gliadins encoded by the A and D-genome. Loss of the α-gliadin locus from the short arm of chromosome 6D resulted in a significant decrease in the presence of T-cell stimulatory epitopes but also a significant loss of dough functionality. Same results were found in studies of van Herpen et al. (2006) who showed that T-cell stimulatory epitopes were more abundant in α-gliadins encoded by the D genome, and Molberg et al. (2005) who demonstrated that the immunodominant 33mer fragment of α-gliadin was encoded by chromosome 6D (and hence absent from diploid einkorn and tetraploid wheats). This suggests that wheat varieties without D-genom result in lower coeliac activity. Nevertheless, there are still other groups of gluten protein that also contain coeliac active sequences.

Conventional breeding may therefore be used to select for gluten protein fractions with lower contents of coeliac epitopes. Molecular breeding approaches can also be used to specifically downregulate coeliac-toxic proteins or mutate coeliac epitopes within individual proteins. A combination of these approaches may therefore be used to develop a “coeliac-safe” wheat. However, this remains a formidable challenge due to the complex multigenic control of gluten protein composition. Furthermore, any modified wheats must retain acceptable properties for making bread and other processed foods. Not surprisingly, such coeliac-safe wheats have not yet been developed despite over a decade of research.

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