Structure-function studies of the cyanobacterial carboxysome and its role in the carbon concentration mechanism

蓝藻是一种光合细菌，其生态功能是作为微型植物，从大气中去除二氧化碳并将其转化为生物分子。尽管它们的“原始”性质和体积很小，但它们几乎出现在所有可以想象到的栖息地，特别是在开阔的海洋中，它们的天文数字数量构成了食物链的基础。蓝藻在地球整体碳预算的“信用”方面占很大一部分，使它们成为全球变暖等现象的关键参与者。蓝细菌在固碳方面特别有效的一个特点是，它们有能力将RuBisCO酶（负责捕获二氧化碳的关键步骤）组织成一种叫做羧酸体的结构。羧基小体的直径在100到200纳米之间，以细胞的标准来看是巨大的，主要由RuBisCO组成，由一层薄薄的蛋白质壳包围，具有类似病毒的二十面体几何形状。这个外壳似乎至少在一定程度上起到了阻挡二氧化碳逃逸的作用，使RuBisCO（已知最慢、效率最低的酶之一）有机会将二氧化碳捕获为糖。这种外壳是由少量的小蛋白质构成的，它们的行为就像规则的六边形瓷砖，能够组装成任意大小的薄片。了解使蓝藻中光合作用这方面如此有效的详细原理是至关重要的。我的实验室将研究控制羧基体结构的建筑原理，方法是分别制造所有的成分，然后研究它们是如何组装的。我们还将使用x射线晶体学来建立单个组件的原子尺度模型，并研究它们如何相互作用以构建更大的子组件。

Cyanobacteria are photosynthetic bacteria, and function ecologically as microscopic plants that remove carbon dioxide from the atmosphere and incorporate it into biological molecules. Despite their "primitive" nature and tiny size, they occur in almost all conceivable habitats, especially in the open ocean where their astronomical numbers form the base of the food chain. Cyanobacteria are responsible for a large fraction of the "credit" side of the planet's overall carbon budget, making them key players in phenomena such as global warming. One of the specializations that make cyanobacteria especially efficient at carbon fixation, is their ability to organize the enzyme RuBisCO (responsible for the critical step where carbon dioxide is captured) into structures called carboxysomes. Carboxysomes are, at 100 to 200 nm in diameter, enormous by cellular standards, and are comprised mostly of RuBisCO, surrounded by a thin protein shell with virus-like, icosahedral geometry. This shell appears to work, at least in part, as a barrier to carbon dioxide escape allowing RuBisCO (one of the slowest and least efficient enzymes known) to have a chance to capture it as a sugar. The shell is built from a handful of small proteins that behave as regular hexagonal tiles, capable of assembling into sheets of arbitrary size. It is of fundamental importance to understand the detailed principles that make this aspect of photosynthesis in cyanobacteria so efficient. My lab will investigate the architectural principles governing carboxysomal structure by making all of the components separately, and then investigating how they assemble. We will also be using X-ray crystallography to build atomic-scale models of the individual components, and studying how they interact to build larger sub-assemblies.