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

阳光的光合作用转化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。能量转化蛋白复合物在膜上100纳米尺度（称为介观水平）的精确结构定位是生物能量转化功能和调控的关键因素。缺少关于介观特征及其对环境线索的动态响应的信息代表了知识库的重大空白。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，不仅对光合作用的基础研究有直接影响，而且了解植物栖息地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成分。在这项工作中开发的计算机模型有可能揭示光合作用机制的基本设计原理，这些原理可用于确定设计作物植物的新方法。类囊体膜的介观特性和动力学在作物改良中的重要性一直被忽视。此外，建议的工作非常注重学生和博士后的高质量教育。根据以往nsf资助本科生的成功经验，将从代表性不足的群体中招募6名本科生，并提供支持的研究培训机会。本研究的目的是揭示在堆积状颗粒类囊体膜（约占整个类囊体膜的60%）中，脂质组成和可逆蛋白磷酸化对介观蛋白质组织及其动力学的作用。核心假设是，脂质基质的物理化学性质和颗粒宿主蛋白的磷酸化是颗粒中超分子蛋白排列的关键决定因素。PI和他的合作者将确定脂质基质对颗粒中超分子蛋白质组织的影响。通过冷冻破裂膜上的冷冻扫描电子显微镜（SEM），对野生型（WT）和脂质和脂肪酸突变体在颗粒膜上的光系统II （PSII）排列进行了绘制和数学分析。接下来，将通过比较WT蛋白的PSII图谱与蛋白高磷酸化或低磷酸化突变体的PSII图谱，确定可逆蛋白磷酸化诱导的介观动力学。最后，控制蛋白质集合行为的力将通过应用粗粒计算机模型来确定。该项目将在介观水平上对光合膜的结构-功能关系提供前所未有的见解，并通过改变脂质/脂肪酸组成或蛋白质磷酸化模式对介观蛋白质组织和PSII超复合物稳定性的变化进行深入的结构表征。这一贡献是重要的，因为它确定了控制和调节堆叠类囊体膜中超分子蛋白质动力学的中心机制，这些超分子蛋白质动力学是在不断变化的环境中有效的光合能量转换所必需的。这个美国/以色列合作项目由美国国家科学基金会和美以两国科学基金会支持。

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.