NSF/MCB-BSF:Understanding Photosynthetic Energy Conversion on the Mesoscale

太阳光的光合作用转换需要嵌入叶绿体类囊体膜内的纳米级蛋白质复合物之间的结构协调。能量转换蛋白复合物在100纳米长度尺度（称为介观水平）上在膜中的精确结构定位是生物能量转换的功能和调节的关键要素。缺少有关中观特征及其对环境线索的动态响应的信息，这是知识库中的一个重大空白。特别是，目前还不清楚是什么因素决定了类囊体膜的介观特征，以及涉及到什么物理化学力。拟议的工作旨在填补这一关键空白。了解植物如何在介观长度尺度上优化和调节光合能量转换不仅会对基础光合作用研究产生直接影响，而且通过了解植物生境的变化如何通过介观膜特征的改变来控制光合性能，具有很强的生态生理学意义。将在拟议的工作中开发的计算机模型有可能解开光合机制的基本设计原则，可用于识别设计作物的新方法。类囊体膜的介观特性和动态在作物改良中的重要性一直被忽视。此外，拟议的工作重点是学生和博士后的高质量教育。根据以往与NSF支持的本科生的成功经验，将从代表性不足的群体中招募六名本科生，并提供支持的研究培训机会。本研究的目的是解开的作用的脂质组成和可逆的蛋白质磷酸化介观蛋白质组织和其动态堆叠基粒类囊体膜（覆盖约60%的整个类囊体膜）。中心假设是，脂质基质的物理化学性质和基粒宿主蛋白质的磷酸化是基粒中超分子蛋白质排列的关键决定因素。PI和他的合作者将确定脂质基质对基粒中超分子蛋白质组织的影响。光系统II（PSII）安排在基粒膜将映射和数学分析野生型（WT）和脂质和脂肪酸突变体冷冻断裂膜上的冷冻扫描电子显微镜（SEM）。接下来，可逆的蛋白质磷酸化诱导的介观动力学将通过比较WT蛋白质的PSII图谱与具有蛋白质高磷酸化或低磷酸化的突变体的PSII图谱来确定。最后，将通过应用粗粒度计算机建模来确定控制蛋白质集合行为的力。该项目将提供前所未有的深入了解光合膜的结构-功能关系的介观水平，除了深入的结构表征的变化介观蛋白质组织和PSII超复合物的稳定性的脂质/脂肪酸组成或蛋白质磷酸化模式的改变。这一贡献是显着的，因为它确定了中央机制，控制和调节超分子蛋白质动力学堆叠类囊体膜所需的高效光合能量转换在不断变化的environments.This合作美国/以色列项目是由美国国家科学基金会和美国-以色列两国科学基金会的支持。

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.