Research objectives and content
Photosystem II (PS II) is one of the two thylakoid membrane bound pigment protein complexes involved in oxygenic photosynthesis. lt's biological importance is due to its unique water-splitting activity. PS 11 is a complex system, made up from the association of several protein subunits, in which are bound several electron transfer cofactors. such quinones, pheophytin, a Mn cluster (containing 1 metallic ions), etc. Only partial structural information is available about PS II. One of the main goal of studies performed on PS II is the identification of the binding site and the structure of the Mn cluster, as well as understanding its chemical mechanism. The present project aims to address these questions using several kind of EPR, magnetic susceptibility and optical absorption studies together with the appropriate membrane protein purification biochemistry. The Mn cluster photochemistry, which has been newly discovered in the Saclay lab [Boussac A. et al., Biochemistry (1996) in press] will be investigated and will be used to provide samples with quantitative amounts of the state giving rise to the g-4 EPR signal. EPR on oriented sample, high field and pulsed EPR will be useful in providing data on the nature of the so-catled "g=4 state" of the Mn cluster, on its relaxation characteristics and on the origin of its EPR signal.
In order to gain much more information about the structure of the Mn cluster, this project will include analogous investigations on Mn model systems.
Training content (objective, benefit and expected impact)
I expect to learn to use powerful spectroscopic tools, which may be usefully applied to the investigation of metalloenzyme chemistry. I think that the Saclay centre can provide the support necessary for such kind of studies, since its research groups are at the forefront of
interdisciplinary research in this field. Moreover, the extraordinarily range of equipment available in Saclay and their expertise in molecular enzymology represents a unique environment for the development of high level spectroscopic studies using an interdisciplinary approach. I also expect that, during this training, I will gain much more than technical expertise; I consider that the intellectual environment is ideal for the exchange of scientific ideas and for developing new ideas. My current lab and the lab at Saclay hope to use my association with Saclay as a basis for setting up of future collaborations of' mutual interest on diverse metalloproteins.
Links with industry / industrial relevance (22)