Structural studies of cyanobacterial carboxysomes

蓝藻是一种细菌，像植物一样，可以利用阳光产生的能量将二氧化碳和水转化为糖。它们特别擅长在生命所需的微量元素非常稀缺的情况下做到这一点，因此它们是开阔海洋中最重要的“植物”。这使得蓝藻成为全球变暖的重要参与者，因为开阔的海洋是从大气中大量净清除二氧化碳的主要环境。蓝藻的生活方式之一是收集一种名为Rubisco的酶，这种酶负责将二氧化碳合并到糖中，形成称为羧基体的异常大的结构。耐人寻味的是，羧基体表面上看起来非常像病毒，病毒也是由一个包裹着功能核心的蛋白质壳组成的。这个外壳似乎起到了阻碍二氧化碳逃逸的屏障的作用，从而使Rubisco有机会通过化学反应永久地捕获二氧化碳。Rubisco是已知的速度最慢、效率最低的酶之一。我的实验室计划通过生化解剖这个壳，并检查每一块的外观和功能，来研究它是如何发挥作用的。我们将在细菌中制造每一种壳蛋白，然后在提纯蛋白质并将其培养成晶体形式后，使用一种名为X射线结晶学的技术来建立一个逐个原子的模型。壳蛋白也将作为复合体进行研究，这将使我们能够模拟更大部分的羧体是如何组装在一起的。对衍生模型的仔细检查应该会给出许多关于每种蛋白质是如何贡献的线索，产生一些想法，然后我们可以通过进一步的实验工作来跟进。

Cyanobacteria are a type of bacteria that, like plants, can use energy derived from sunlight to turn carbon dioxide and water into sugar. They are especially good at doing this under circumstances where the trace elements needed for life are very scarce, and for this reason are the most important "plants" in the open ocean. This makes cyanobacteria important players in global warming, as the open ocean is the main environment in which there is a significant net removal of carbon dioxide from the atmosphere. One of the specialisations that cyanobacteria have adopted for their lifestyle is to collect the enzyme, called RuBisCO, that is responsible for incorporating carbon dioxide into sugars, into unusually large structures called carboxysomes. Intriguing, carboxysomes look superficially very much like viruses, which also are comprised of a protein shell surrounding a functional core. This shell appears to work as a barrier that impedes the escape of carbon dioxide thus allowing RuBisCO, one of the slowest and least efficient enzymes known, to have a chance to capture it permanently with a chemical reaction. My lab plans to investigate how this shell functions by dissecting it biochemically and examining what each piece looks like and does. We will make each shell protein in bacteria, and then, after purifying the protein and growing it in crystalline form, use a technique called X-ray crystallography to build an atom-by-atom model. The shell proteins will also be investigated as complexes that will allow us to model how larger portions of the carboxysome are put together. Close examination of the derived models should give numerous clues as to how each protein contributes, generating ideas which we can then follow up by further experimental work.