Protein organizations underpinning Wzm/Wzt dependent bacterial polysaccharide production

细菌将自己包裹在一层分子的外壳中，这些分子主要由复杂的多糖(字面意思是许多糖；纤维素和淀粉是常见的例子)组成。然后，这些外衣就成为细菌与环境相互作用的主要表面。对于病原菌来说，这是宿主“看到”它们的一个主要方面，使这些多糖有可能用作疫苗。这些毛皮也是杀菌病毒的目标；因此，细菌有强烈的动机进化出新的毛皮变体来躲避这种攻击，已知的毛皮变体有数千种。制造这些多糖的机制虽然仍然相当复杂和多样化，但可以回收许多关键成分和方法。我们的目标是使用各种工具来研究这种机器，包括x射线结晶学，这将使我们能够看到这些机器的原子细节。这将使我们能够详细了解这些成分是如何工作的，然后通过使用基因工具干扰蛋白质来测试这些想法。我们的直接目标是热带根瘤菌，这是一种为豆类和玉米固定氮素的有用生物。这种生物体形成了一层含有不同寻常的糖岩藻糖和脱氧塔尔糖的多糖衣。我们的目标是研究这些添加糖的酶是如何工作的。这种生物体还测量其外壳糖到相当精确的预先指定的长度；然而，建立糖链的机械缺乏在其他糖测量系统中看到的典型组织。我们计划对测量机制进行更详细的研究。此外，该机器将乙酰基添加到脱氧塔尔糖残基的子集中。已公布的数据暗示，它可能是以这样一种方式这样做的：只修改糖的顶部，帮助阻止病毒，而病毒则无法识别下半部分。我们想要检验这一假设，并了解这种分区控制是如何实现的。从长远来看，我们希望通过了解不同的具有独特性质的多糖合成机器，将出现足够的了解，以便能够详细预测所有细菌的糖衣结构。

Bacteria sheath themselves in a coat of molecules made predominantly from complex polysaccharides (literally many-sugar; cellulose and starch are familiar examples). These coats then are then the dominant surface with which bacteria interact with their environment. For pathogenic bacteria, this is a major aspect of the way the host "sees" them, making these polysaccharides potentially useful as vaccines. These coats are also targeted by bacteria-killing viruses; as a result, bacteria have strong incentives to evolve new coat variants to escape such attacks, and there are thousands of coat variants known. The machinery that builds these polysaccharides, while still quite complex and diverse, recycles many of the key components and approaches. We aim to study this machinery, using a variety of tools, including x-ray crystallography which will allow us to see these machines in atom-by-atom detail. This will allow us to develop a detailed understanding of how these components work, and then test these ideas by perturbing the proteins using genetic tools. Our immediate target is the bacterium Rhizobium tropici, a useful organism that fixes nitrogen for beans and maize. This organism builds a polysaccharide coat incorporating the unusual sugars fucose and deoxytalose. We aim to investigate how these sugar adding enzymes work. This organism also measures its coat sugars to a fairly exact pre-specified length; however, the machinery building the saccharide chains lacks the typical organization seen in other saccharide measuring systems. We plan to investigate the measurement mechanism in some detail. In addition, the machinery adds an acetyl group to a subset of the deoxytalose residues. Published data hints that it may be doing so in such a way that only the top portion of the sugar is modified, helping thwart viruses which then would not recognize the bottom half. We want to test this hypothesis, and understand how such zonal control is achieved. Long term, we hope by understanding different such polysaccharide synthesis machines with unique properties, sufficient understanding will emerge to allow detailed predictions of the saccharide coat structures of all bacteria.