Structural studies of cyanobacterial carboxysomes

蓝细菌是一种细菌，像植物一样，可以利用来自阳光的能量将二氧化碳和水转化为糖。在生命所需的微量元素非常缺乏的情况下，它们尤其擅长这样做，因此是公海中最重要的“植物”。这使得蓝细菌在全球变暖中扮演重要角色，因为开放的海洋是大气中二氧化碳净清除的主要环境。蓝藻为它们的生活方式所采用的专业化之一是收集酶，称为RuBisCO，负责将二氧化碳结合到糖中，进入称为carboxysomes的异常大的结构中。有趣的是，羧基体表面上看起来非常像病毒，也是由围绕功能核心的蛋白质外壳组成。这种壳似乎是一种屏障，阻止二氧化碳的逃逸，从而使已知最慢和最低效的酶之一RuBisCO有机会通过化学反应永久捕获二氧化碳。我的实验室计划通过生物化学方法解剖它，并检查每一块的外观和功能，来研究这个外壳是如何工作的。我们将在细菌中制造每一种外壳蛋白质，然后，在纯化蛋白质并使其以晶体形式生长之后，使用一种称为X射线晶体学的技术来建立一个原子接一个原子的模型。壳蛋白也将作为复合物进行研究，这将使我们能够模拟更大部分的羧基体是如何放在一起的。对衍生模型的仔细检查应该会提供许多关于每种蛋白质如何贡献的线索，从而产生我们可以通过进一步的实验工作来跟进的想法。

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.