Protein organizations underpinning Wzm/Wzt dependent bacterial polysaccharide production

细菌将自己包裹在一层主要由复杂多糖（字面意思是许多糖;纤维素和淀粉是常见的例子）组成的分子外壳中。然后，这些涂层是细菌与环境相互作用的主要表面。对于致病菌，这是宿主“看到”它们的方式的一个主要方面，使得这些多糖可能用作疫苗。这些外壳也是杀细菌病毒的目标;因此，细菌有强烈的动机进化新的外壳变体以逃避这种攻击，并且已知有数千种外壳变体。构建这些多糖的机制虽然仍然相当复杂和多样，但却包含了许多关键成分和方法。我们的目标是研究这种机制，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的细节。这将使我们能够详细了解这些组件如何工作，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氮的有用生物。这种微生物构建了一个多糖外壳，包含不寻常的糖岩藻糖和脱氧塔罗糖。我们的目标是研究这些糖添加酶是如何工作的。这种微生物也测量其外壳糖到相当精确的预定长度;然而，构建糖链的机器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，该机制将乙酰基添加到脱氧塔罗糖残基的子集。已发表的数据暗示，它可能是以这样一种方式做到这一点的，即只有糖的顶部被修改，帮助阻止病毒，然后不会识别下半部分。我们想验证这个假设，并了解这种区域控制是如何实现的。从长远来看，我们希望通过了解具有独特性质的不同多糖合成机器，将出现足够的理解，以便详细预测所有细菌的糖外壳结构。

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.