Résumé
Astringency is an important organoleptic property of plant-based food. It is attributed to interactions of tannins, which are polyphenolic compounds, with salivary proteins and especially proline rich proteins (PRPs), which belong to the group of intrinsically unstructured proteins (IUPs). Tannins play an important part in plant defence mechanisms. Indeed, they have an antinutritional effect as they inhibit digestive enzymes. Production of salivary PRPs is thus an adaptation process to tannin-rich diets. The purpose of this work is to provide a closer look at PRP•tannin supramolecular edifices in solution, using a mass spectrometry (MS) approach. The human salivary proteins IB5, a basic PRP, and II-1, a glycosylated PRP, have been produced by heterologous expression. After purification, both proteins have beencharacterized by MS using electrospray (ESI) and Matrix-Assisted Laser Desorption Ionisation (MALDI) sources. The study of the interaction between IB5 and model tannins by ESI-MS confirmed the presence of IB5•tannin non-covalent complexes in solution and provided new information on their stoichiometries. Competitive interaction experiments between IB5 and two tannins, along with IB5•tannin complexes dissociation studies revealed the impact of the main tannin chemical features on this interaction. Structural studies performed on IB5•tannin edifices by Collision Induced Dissociation (CID) and Electron Capture Dissociation (ECD) MS/MS experiments and by ion mobility spectrometry coupled with MS showed the presence of several interaction sites on IB5 and conformational changes arising from the interaction.