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

蓝藻是一种光合作用细菌，在生态学上起着微型植物的作用，可以从大气中去除二氧化碳，并将其结合到生物分子中。尽管它们的“原始”性质和微小的体型，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，它们的天文数字构成了食物链的基础。蓝藻占地球总碳预算的很大一部分，使它们成为全球变暖等现象的关键参与者。使蓝藻在固碳方面特别有效的一个特长是，它们能够将Rubisco酶(负责捕获二氧化碳的关键步骤)组织成称为羧基体的结构。羧体直径在100到200纳米之间，以细胞标准衡量是巨大的，主要由Rubisco组成，周围有一层薄的蛋白质外壳，具有病毒样的二十面体几何形状。这个外壳似乎至少在一定程度上是作为二氧化碳逃逸的屏障，使Rubisco(已知的速度最慢、效率最低的酶之一)有机会将其捕获为糖。壳层由几个小蛋白质组成，这些蛋白质的行为就像规则的六角形瓷砖，能够组装成任意大小的薄片。了解蓝藻光合作用这一方面如此高效的详细原理是非常重要的。我的实验室将通过单独制造所有组件，然后调查它们是如何组装的，来研究支配羧体结构的建筑原则。我们还将使用X射线结晶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来建立更大的子组件。

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.