Microbial Control of Carbon Fixation

地球上大约三分之一的光合作用是由水生细菌完成的。在细胞内没有膜结合的隔间的情况下，这些生物通过将它们紧密地包装在称为羧基体的蛋白质隔间内，为固碳酶创造了一个良好的环境。尽管羧体在全球碳循环中的重要性以及它们作为合成生物学平台的潜力，但人们对羧体的组装过程仍然知之甚少。这项研究将阐明指定羧基体内大小、数量和内部环境的分子机制。它将融合生化方法、合成生物学和荧光显微镜来探索整个羧基体随时间推移的组装过程，并将这一过程置于细胞生理学的背景下。对羧基体形成的基本生物学机制的了解将为未来这些隔室的工程奠定基础。为此，该项目将进一步推动NSF扩大科学和工程研究潜力的使命，无论是通过改善自然碳固定，还是为活细胞内的其他敏感化学反应建造纳米工厂。该项目还将提供理想的跨学科教育和培训计划。更广泛地说，羧体工作的最终目标是改进新功能的工程设计。这种类似生命的合成系统可以被赋予隔离和遏制与细菌细胞质不相容的反应的能力，或者在碳固定的基础上改进，以创造更有效、更活的二氧化碳补救剂。降低大气中的二氧化碳(一种主要的温室气体)的水平将阻止气候变化，从而带来重大的社会效益。随着大气中的二氧化碳水平接近400ppm，了解固定碳的生物学机制变得越来越重要。很大一部分二氧化碳是由光合作用的蓝藻修复的，它将固定碳所需的机械集中到称为羧基体的蛋白质微室中。在细长聚球藻中，这些细胞器由一层外壳蛋白组成，包裹着Rubisco酶和碳酸氢酶的基质。尽管它们对全球碳循环很重要，但控制这些复杂蛋白质机器组装的因素却知之甚少。哈佛医学院的Pamela Silver博士和她的团队将利用生化重组、遗传扰动和定量活细胞显微镜来研究羧体生物发生的空间和时间组织的分子基础和代谢结果。

Approximately one third of all the photosynthesis on earth is performed by aquatic bacteria. In the absence of membrane-bound compartments inside their cells, these organisms create a favorable environment for carbon-fixing enzymes by tightly packaging them inside protein compartments called carboxysomes. Despite the importance of carboxysomes to the global carbon cycle and their potential to serve as a platform for synthetic biology, the carboxysome assembly process is still poorly understood. This research will elucidate the molecular mechanisms specifying the size, number, and internal environment inside carboxysomes. It will blend biochemical approaches, synthetic biology, and fluorescence microscopy to explore the assembly process of whole carboxysomes over time, and to place this process in the context of cellular physiology. An understanding of the basic biological mechanisms by which carboxysomes are formed will lay the groundwork for future engineering of these compartments. Toward this end, this project will further the NSF's mission of expanding science and engineering research potential, whether by improving on natural carbon fixation or building nanoscale factories for other sensitive chemical reactions within living cells. This project will provide also an ideal interdisciplinary educational and training program. More broadly, the ultimate goal of the carboxysome work is to improve the engineering of novel functionalities. Such a synthetic life-like system could be endowed with the ability to sequester and contain reactions otherwise incompatible with the bacterial cytoplasm, or improve upon carbon fixation to create more efficient, living remediators of carbon dioxide. Reducing the levels of atmospheric carbon dioxide, a major greenhouse gas, would forestall climate changes, and therefore offer major societal benefit.As atmospheric carbon dioxide levels are approaching 400 ppm, understanding biological mechanisms of carbon fixation is becoming increasingly important. A large fraction of carbon dioxide is remediated by photosynthetic cyanobacteria, which concentrate the machinery required to fix carbon into proteinaceous microcompartments called carboxysomes. In Synechococcus elongatus, these organelles, are composed of a layer of shell proteins surrounding a matrix of the enzymes RuBisCO and carbonic anhydrase. Despite their importance to the global carbon cycle, the factors controlling assembly of these complex protein machines are poorly understood. Dr. Pamela Silver and her group at the Harvard Medical School will employ biochemical reconstitution, genetic perturbations, and quantitative live-cell microscopy to study the molecular basis and metabolic consequences of the spatial and temporal organization of carboxysome biogenesis.