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

蓝细菌是光合细菌，在生态学上起着微观植物的作用，从大气中去除二氧化碳并将其纳入生物分子。尽管它们的“原始”性质和微小的尺寸，它们出现在几乎所有可以想象的栖息地，特别是在开放的海洋中，它们的天文数字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。使蓝细菌在碳固定方面特别有效的专门化之一是它们能够将酶RuBisCO（负责捕获二氧化碳的关键步骤）组织成称为carboxysomes的结构。羧基体的直径为100至200 nm，以细胞标准衡量是巨大的，并且主要由RuBisCO组成，被具有病毒样二十面体几何形状的薄蛋白质壳包围。这种外壳似乎至少部分地作为二氧化碳逃逸的屏障，允许RuBisCO（已知最慢和最低效的酶之一）有机会将其捕获为糖。外壳是由少量的小蛋白质组成的，这些蛋白质的行为就像规则的六边形瓦片，能够组装成任意大小的薄片。理解使蓝藻光合作用如此有效的详细原理是至关重要的。我的实验室将通过分别制造所有组件，然后研究它们如何组装，来研究控制羧基体结构的建筑原理。我们还将使用X射线晶体学来构建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.