Internal motions in biomolecules studied by NMR spectroscopy : an application to major urinary protein-1 and its complex with 2-methoxy-3-isobutylpyrazine

Since many biological processes occur on the μs to ms time scale, internal dynamics on that time scale is believed to be related to biological functionality. The characterization of internal dynamics is thus an important issue to improve our understanding of the biological activity of macromolecules, such as proteins, RNA and DNA fragments. Solution NMR spectroscopy, in particular relaxation measurements, is well suited for the determination of exchange rates on that slow time scale. The formation of a small pheromone-protein complex is associated with some kind of internal rearrangements, necessary to accomodate the ligand. In this work, we are interested in the changes in internal dynamic upon the binding of a model odorant molecule, the 2-methoxy-3-isobutylpyrazine, to Major Urinary Protein I, MUP I. The study of the internal dynamics of both apo- and holo-MUP I has been carried out with the goal of monitoring the differences between the two states of the protein. In fact, impressive changes in chemical shifts are present between the two forms, indicating that some internal rearrangements have taken place. New and more classical experiments have been applied to MUP I in order to gain insight into the different types of motions that occurs at different time scales. The presence of chemical exchange has been identiτed in apo-MUP I using the classical Carr-Purcell-Meiboom-Gill experiment on single quantum 15N magnetisation. Surprisly, in holo-MUP I no presence of chemical exchange has been found, so in which time scale are the dynamics which leads to the release of the ligand in the environnment? Slow motions (ms-μs) in both apo- and holo-MUP I have been found using a new experiment, which highlight the presence of correlated motions in the backbone of proteins.