Fig. 1. The toxic mechanism of Coeliac Disease, from Metcalf (2003).

Fig. 2. Example of a toxic sequence in the gliadin molecule. The schematic shows the typical domain structure of gliadin (I–V), with a small part of domain I (marked by *) containing the toxic sequence.

Fig. 3. Phylogenetic tree of cereals. This representation shows how close plants are related. The smaller the distance, the closer the homology. The circle contains the cereals considered toxic to CD patients: Secale (rye), Triticum (wheat, durum), Avena (oats) and Hordeum (barley). Oryza (rice) and Sorghum are more distant; these plants are considered safe.

Positive matches of algorithms with other cereal proteins, from Vader et al. (2000)

Database searches with the search algorithms.

The search algorithms reveal many matches in the gluten, hordeins, and secalin sequences but very few in the avenin sequences. The predictive algorithm 2 (QXPQXP[YFWIL]) and the less strict variants of that algorithm have no matches in the avenin database. The novel T-cells stimulatory gluten peptide (QQPFPQQPQQPFPQ) is also found in the hordeins and secalin but not in the avenins. X stands for any amino acid.

The table shows the number of matches for the various search algorithms for protein sequences from gluten, hordein (barley), secalin (rye) and avenin (oats). This number should be regarded with some caution since the number of sequences available in the database also determines it.