Photoprotection against Oxidative Stress
Harvesting solar photons is essential for ensuring the proper bioenergetics balance in photosynthetic organisms. The photosynthetic apparatus is designed to harvest solar photons and to transfer the energy to photosynthetic reaction centers, where the excitation energy is transduced into chemical potential energy. In the presence of strong light the system may become overexcited, and the presence of excitation energy in excess may lead to harmful oxidative stress. It has been known for several years that, in plants and algae, there is a rapid (measured in seconds) feedback response from the photosynthetic apparatus to exposure to high light intensities, leading to the appearance in the photosynthetic membrane of energy traps which drain the excess energy from the system. This mechanism is denoted NPQ for Non-Photochemical Quenching of the energy. Among the deleterious products of photosynthesis, one of the most harmful is the triplet state of chlorophyll, the energy of which is sufficient to sensitize singlet oxygen. To avoid this reaction in an oxygen-rich environment, the chlorophyll triplet states are efficiently quenched by carotenoid molecule in photosynthetic plant complexes.
Our team has played an essential role in characterising some of the mechanisms underlying NPQ as well as efficient Chlorophyll triplet quenching. As these mechanisms in both processes involve carotenoid molecule, we are extensively characterising the physco-chemical properties of these essential molecules, in i) their isolated state, ii) in artificial dyads mimicking photosynthesis and iii) in vivo.
Modelling the Early Steps of Photosynthesis
Comprehensive modelling of photosynthetic proteins function requires both the development of complex theoretical frameworks, and the conception of experiments designed to test the implication of these frameworks. We have entered into a large scale project –supported by an ERC advanced grant awarded to B. Robert- to address the basic concepts underlying the light-harvesting and charge separation processes in photosynthesis. We are involved in studies concerning the LH2 from purple bacteria as well as the proteins from the LHC family of higher plants and algae.
The molecular simulation group of the team has extensively developed tools for performing molecular simulations of micellar systems in parallel with its own interest on enhanced simulation sampling in molecular dynamics and molecular dielectric approaches to ion recognition. Long chain fatty acid (linoleic acid) were studied in particular, and used as templates for nanocluster of metals to develop new potential force fields for detergents commonly used to solubilize membrane proteins. These studies are used to perform molecular simulations of isolated LH2 in different detergent environments. We have the project in the coming years, to extend our studies to larger systems by using coarse-grained methodology.
Phycobilisome and FNR
Phycobilisome (PBS) is a large and abundant pigment-protein complex that harvests light for photosynthetic reactions in cyanobacteria. We are interested in gene regulation of phycobilisome biogenesis in these organisms. Purified PBS contains significant amounts of a 46 kDa Ferredoxin-NADP oxidoreductase (FNR) a protein mainly involved in the last step of linear oxygenic photosynthesis, providing NADPH for CO2 assimilation and other reductive metabolism, but also postulated to be involved in NADPH oxidation during respiration. Some cyanobacteria are able to accumulate two FNR isoforms encoded by the unique petH gene, and we have shown that different transcripts are involved in a new mechanism of translation regulation that results in FNR isoform accumulation. We wish to determine the molecular basis of the FNR translation initiation, and on the other understand the physiological role of each of FNR the isoforms.
The team is involved in developing original methods of super-resolution microscopy, which we plan to use for studying the structure of the photosynthetic membrane. Our current resolution on such system is about 15 nm, i.e. about the size of a single photosystem.
ROBERT Bruno [Chercheur - CEA]
Département de Biochimie, Biophysique et Biologie Structurale [Responsable]
Laboratoire Bioénergétique Membranaire et Stress [Responsable]
bruno.robert 01 69 08 66 84 Saclay - Bât 532