Protein organizations underpinning Wzm/Wzt dependent bacterial polysaccharide production

细菌把自己包裹在一层分子外衣中，这些分子主要是由复杂的多糖构成的（字面上是多糖类，纤维素和淀粉是我们熟悉的例子）。这些外壳是细菌与环境相互作用的主要表面。对于致病菌来说，这是宿主“看到”它们的方式的一个主要方面，使这些多糖有可能用作疫苗。这些外壳也是杀菌病毒的目标；因此，细菌有强烈的动机进化出新的外壳变体来逃避这种攻击，已知的外壳变体有数千种。制造这些多糖的机制，虽然仍然相当复杂和多样，但回收了许多关键成分和方法。我们的目标是研究这种机器，使用各种工具，包括x射线晶体学，这将使我们能够看到这些机器在原子一个原子的细节。这将使我们能够详细了解这些成分是如何工作的，然后通过使用遗传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的有用生物。这种生物构建了一层含有不寻常的糖和脱氧糖的多糖外壳。我们的目标是研究这些加糖酶是如何工作的。这种生物也测量它的外壳糖到相当精确的预先指定的长度；然而，构建糖链的机制缺乏在其他糖测量系统中看到的典型组织。我们计划详细研究测量机制。此外，该机制在脱氧糖残基的一个子集上添加一个乙酰基。公开的数据暗示，它可能是这样做的，只有糖的顶部部分被修改，帮助阻止病毒，然后不能识别底部的一半。我们想要验证这一假设，并了解这种层状控制是如何实现的。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，能够对所有细菌的糖包被结构进行详细的预测。

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.