Structure and Function Can Determine Important Features in Allergenicity: Investigations on the Group I Allergens of the Grasses

The structure of an allergen plays a crucial role in type I allergy. It is involved in the sensitization process as well as in allergic reactions that are caused by repetitive exposure. Here, we focused on the abundant group I allergens of grass pollen, which are known for their IgE inducing potential. We identified at least four independent IgE-binding regions (conformational epitopes) on the molecule. A few continuous epitopes were determined, but they seem to be of minor relevance. As regards post-translational modifications we detected disulfide formations, one Nglycan of the complex type and two hydroxylated proline residues. All these modifications increased the allergenicity. Additionally it was shown that IgE cross-reactivity to unrelated proteins such as tomato is caused by similarities in carbohydrate moieties. Like several food allergens e.g. Act c 1 (kiwi fruit), Gly mBd 30K (soybean) and the dust mite allergen Der p 1, the grass pollen allergen Phl p 1 is a cysteine protease. We proved this by use of specific substrates, specific inhibitors, and by comparison of the protein sequences. In analogy to Der p 1 we deduce that Phl p 1 might enhance the permeability of the epithelium, influence T helper cells to cause a bias to Th2, and increase the IgE production of plasma cells. Thus, the group I allergens seem to be important components in a pollen extract which can mediate sensitization and enhance the triggering of symptoms leading to a persistence of grass pollen allergy. (Internet Symposium on Food Allergens 1999, 1(3):95-101) grass group I allergens type I allergy post-translational modifications epitope mapping protease