Gluten proteins are the main storage proteins within cereal grains such as wheat, rye and barley. Consumption of these cereals can lead to serious digestive problems in those with Coeliac disease, an autoimmune disorder, that affects 1-2% of the global population. The only solution for these patients is adherence to a strict gluten-free diet; however, symptoms persist in about 30% of patients despite committing to this strict regimen.
These persistent symptoms may arise from the presence of gluten-containing grains from agricultural co-mingling, that is cross-contamination occurring during cereal harvesting due to the presence of weeds. In this study, the most common weed infesting grain fields in Australia: ryegrass, family Lolium, was studied This grass has small dense seeds that are difficult to eliminate during automated grain cleaning. Ryegrass, like wheat and other cultivated crop species is a member of the grass species (Poaceae) wherein the storage proteins comprise gluten-like proteins.
In this study we developed a novel proteogenomic approach to identify 30 gluten-like proteins with potential immunogenic properties from cereal species underrepresented in public protein sequence repositories. Herein, 32 ryegrass genotypes were analysed by ELISA and LC-MS/MS. Data were processed and analysed using in-house developed workflows, in which a novel database was constructed from transcriptomic and genomic data. Amino acid substitution searches were performed supported by a peptide validation algorithm. Primary sequence alignments were used to filter gluten proteins and identify sequence regions with epitope-like features and thereby potential immunogenic properties. The proteins aligned to five protein types with known immune-reactivity: omega-gliadin, gamma-gliadin, high-molecular-weight glutenin, avenin and avenin-like proteins. Protein motif searching uncovered potential immunotoxic peptides similar to wheat, barley and oats. The next stage will be to explore whether these non-traditional gluten sources enter the food supply chain and to confirm their potential to trigger Coeliac disease.