Highly efficient gluten degradation with a newly identified prolyl endoprotease: implications for celiac disease

Celiac disease is a T cell-driven intolerance to wheat gluten. The gluten-derived T cell epitopes are proline-rich and thereby highly resistant to proteolytic degradation within the gastrointestinal tract. Oral supplementation with prolyl oligopeptidases has therefore been proposed as a potential therapeutic approach. The enzymes studied, however, have limitations as they are irreversibly inactivated by pepsin and acidic pH, both present in the stomach. As a consequence, these enzymes will fail to degrade gluten before it reaches the small intestine, the site where gluten induces inflammatory T cell responses that lead to celiac disease. We have now determined the usefulness of a newly identified prolyl endoprotease from Aspergillus niger for this purpose. Gluten and its peptic/tryptic digest were treated with prolyl endoprotease, and the destruction of the T cell epitopes was tested using mass spectrometry, T cell proliferation assays, ELISA, reverse-phase HPLC, SDS-PAGE, and Western blotting. We observed that the A. niger prolyl endoprotease works optimally at 4-5 pH, remains stable at 2 pH, and is completely resistant to digestion with pepsin. Moreover, the A. niger-derived enzyme efficiently degraded all tested T cell stimulatory peptides as well as intact gluten molecules. On average, the endoprotease from A. niger degraded gluten peptides 60 times faster than a prolyl oligopeptidase. Together these results indicate that the enzyme from A. niger efficiently degrades gluten proteins. Future studies are required to determine if the prolyl endoprotease can be used as an oral supplement to reduce gluten intake in patients.

Natural variation in toxicity of wheat: potential for selection of nontoxic varieties for celiac disease patients

BACKGROUND & AIMS

Celiac disease (CD) is an intestinal disorder caused by T-cell responses to peptides derived from the gluten proteins present in wheat. Such peptides have been found both in the gliadin and glutenin proteins in gluten. The only cure for CD is a lifelong gluten-free diet. It is unknown, however, if all wheat varieties are equally harmful for patients. We investigated whether wheat varieties exist with a natural low number of T-cell-stimulatory epitopes.

METHODS

Gluten proteins present in public databases were analyzed for the presence of T-cell-stimulatory sequences. In addition, wheat accessions from diploid (AA, SS/BB, and DD genomes), tetraploid (AABB), and hexaploid (AABBDD) Triticum species were tested for the presence of T-cell-stimulatory epitopes in gliadins and glutenins by both T-cell and monoclonal antibody-based assays.

RESULTS

The database analysis readily identified gluten proteins that lack 1 or more of the known T-cell-stimulatory sequences. Moreover, both the T-cell- and antibody-based assays showed that a large variation exists in the amount of T-cell-stimulatory peptides present in the wheat accessions.

CONCLUSIONS

Sufficient genetic variation is present to endeavor the selection of wheat accessions that contain low amounts of T-cell-stimulatory sequences. Such materials may be used to select and breed wheat varieties suitable for consumption by CD patients, contributing to a well-balanced diet and an increase in their quality of life. Such varieties also may be useful for disease prevention in individuals at risk.