The photosynthetic conversion of sunlight requires structural coordination between nanometer-sized protein complexes embedded within the thylakoid membrane of chloroplasts. The exact structural positioning of the energy transforming protein complexes in the membrane on the 100 nanometer length scale (called the mesoscopic level) is a key element for the functionality and regulation of biological energy conversion. Missing information about mesoscopic characteristics and their dynamic response to environmental cues represents a significant gap in the knowledge base. In particular, it is not understood what factors determine mesoscopic features in thylakoid membranes and what physicochemical forces are involved. The proposed work aims to fill this critical gap. Knowing how plants optimize and regulate photosynthetic energy conversion on the mesoscopic length scale will not only have a direct impact on basic photosynthesis research but also has a strong eco-physiological component by understanding how changes in plant habitats control photosynthetic performance via modifications in mesoscopic membrane features. The computer model that will be developed in the proposed work has the potential to unravel the underlying design principles of the photosynthetic machinery that can be used for the identification of new approaches to design crop plants. The importance of mesoscopic characteristics and dynamics of thylakoid membranes in improving crop plants has been neglected thus far. Furthermore, the proposed work has a strong focus on high-quality education of students and postdocs. Based upon previous successful experiences with NSF-supported undergraduates, six undergraduates from underrepresented groups will be recruited and offered supported research training opportunities.
The objective of this research is to unravel the role of the lipid composition and reversible protein phosphorylation for mesoscopic protein organization and its dynamics in stacked grana thylakoid membranes (covers about 60% of the whole thylakoid membrane). The central hypothesis is that physicochemical properties of the lipid matrix and the phosphorylation of grana hosted proteins are key determinants for the supramolecular protein arrangement in grana. The PI and his collaborators will determine the impact of the lipid matrix for the supramolecular protein organization in grana. The photosystem II (PSII) arrangement in grana membranes will be mapped and mathematically analyzed for wildtype (WT) and lipid and fatty acid mutants by cryo-scanning electron microscopy (SEM) on freeze-fractured membranes. Next, the mesoscopic dynamics induced by reversible protein phosphorylation will be determined by comparing PSII maps of WT protein with those of mutants with protein hyper- or hypo-phosphorylation. Finally, the forces that control protein ensemble behavior will be determined by applying coarse grain computer modeling. The project will provide unprecedented insight into structure-function relationship of photosynthetic membranes on the mesocopic level and in addition to in-depth structural characterizations of changes in the mesoscopic protein organization and PSII supercomplex stability by alterations of the lipid/fatty acid composition or protein phosphorylation pattern. This contribution is significant because it identifies central mechanisms that control and regulate supramolecular protein dynamics in stacked thylakoid membranes required for efficient photosynthetic energy conversion in ever-changing environments.
This collaborative US/Israel project is supported by the US National Science Foundation and the US-Israel Binational Science Foundation.
