Dr. J. R. Albani, Head of the Laboratoire de Biophysique Moléculaire (University of Lille 1, France) wishes to recruit a fellow researcher for a period of two years. Dr Albani, a specialist of fluorescence spectroscopy and of proteins structure and dynamics, has bought recently a fluorescence lifetime instrument (a TCSPC instrument) and is thus developing new programs for studying proteins properties using fluorescence lifetimes measurements. Two subjects are already available, one on myoglobin and the other on α1-acid glycoprotein. The purpose of the two subjects is to understand the relation between the structure and the dynamics of the protein with its function. Myoglobin binds small molecules such as oxygen while α1-acid glycoprotein binds ligands such as progesterone and propranolol. For myoglobin, do protein dynamics play any important role in binding of small ligands such as oxygen? In fact, structural modification observed upon oxygen binding and their importance could be the results of the internal motions of the proteins. Binding of a ligand could simply be dependent on its diffusion within the protein and thus on the structural flexibility of the protein. These dynamics concern the local and global motions of the protein matrix and the dynamics of the porphyrin embedded in the heme pocket. For α1-acid glycoprotein, what would be the role of the protein pocket structure and dynamics in the ligands binding process? How does the binding process affect the structure and the dynamics of α1-acid glycoprotein in different areas far from the binding site? The two proteins contain a pocket where ligand binding occurs which makes possible to use the same techniques and method in the conception of our projects. Dynamics within different areas of the two proteins can be studied by performing oxygen quenching experiments on fluorophores with different fluorescence lifetimes and bound to the pocket. The rationale for this approach is that a short fluorescence lifetime of the fluorophore compared to a longer fluorescence lifetime of another fluorophore would allow probing a dynamic region closer to the pocket. In fact, it is the lifetime of the excited state of the fluorophore, which is the determining factor in revealing the existence of different domains. While the quenching process retains its dynamic character, the details of this quenching in different domains of the protein as investigated by the oxygen migration process are fundamentally different. For example, the 17.8-ns lifetime of the protoporphyrin IX emission is sufficient to permit oxygen situated in any part of the protein at the instant of fluorophore excitation to reach the porphyrin during the persistence of the excited state; therefore the calculated migration rate k for oxygen through the protein represents an average value for all domains of the protein. For zinc protoporphyrin, on the other hand, the emission lifetime is shorter (2.1 ns) and during the persistence of the excited state, only the few oxygen molecules present in the region of the protein directly surrounding the fluorophore are involved in the quenching process. Thus, with zinc protoporphyrin, we are going to probe the diffusion of oxygen molecules within the pocket and of the amino acids of the pocket itself. However, when tin porphyrin will be used to study the oxygen diffusion, one should expect to obtain information on the dynamics inside the pocket itself. Some of the fluorophores that are going to be used are: protoporphyrin IX (mean lifetime = 17.8 ns), TNS (mean lifetime = 9 ns), calcofluor (mean lifetime = 4.5 ns), Zinc porphyrin (mean lifetime = 2.1 ns) and Tin porphyrin (mean lifetime = 1.2 ns). Finally, Performing static fluorescence anisotropy and anisotropy decay experiment with these different fluorophores in the absence of oxygen and in different conditions of temperature and sucrose would allow us study the strength of the fluorophore interaction with the pocket at different distances from the contact point. Thus, parameters such as the activation energy and the rotational correlation time that are characteristics of the structure of the studied protein area can be put into evidence.
Therefore, we can recruit two persons so that each of them can work on one protein.
2800 euros net, plus travel expenses, plus other allowances.
The person should go back to his country after the two years in France.