Covalent polyphenol modification of a reactive cysteine in the major apple allergen Mal d 1
Jana Unterhauser, Linda Ahammer, Tobias Rainer, Reiner Eidelpes, Sebastian Führer, Bettina Nothegger, Claudia E. Covaciu, Valentina Cova, Anna S. Kamenik, Klaus R. Liedl, Thomas Müller, Kathrin Breuker, Klaus Eisendle, Norbert Reider, Thomas Letschka, Martin Tollinger
Abstract
Naturally occurring polyphenols can modify the molecular properties of food allergens. For the major apple allergen Mal d 1 it has been postulated that chemical reactions with polyphenols cause permanent changes in the tertiary structure, causing a loss of conformational IgE epitopes and reducing allergenicity. In our study, we investigated the effect that reactions with oxidized polyphenols have on the structure of Mal d 1 by mass spectrometry and NMR spectroscopy. We showed that a surface-exposed cysteine residue in this allergen spontaneously reacts with oxidized polyphenols under formation of a defined covalent adduct. Chemical modification of Mal d 1 did not destabilize or perturb the three-dimensional fold, nor did it interfere with ligand binding to its internal pocket. A structural model of the chemically modified apple allergen is presented, which reveals that the bound polyphenol partially covers a conformational IgE epitope on the protein surface.