Unravelling the organisation, composition and dynamics of the plant cellulose synthase complex

纤维素是许多植物细胞壁的主要成分，被认为是世界上最丰富的天然聚合物，也是我们周围自然界的主要成分。木材是由植物细胞壁组成的，特别高的比例（高达70%）的木材是由纤维素组成的。纤维素在决定作物的机械性能方面也很重要，因此在防止谷物和其他作物倒伏方面也很重要。对于工业来说，二次壁的性能直接决定了制成品的性能，例如纸张质量和纺织品中使用的纤维。此外，增加可生物降解原材料比例的迫切需求可以通过使用天然植物纤维而不是玻璃纤维等材料中的合成纤维来填补。由于汽油等化石燃料的使用，全球变暖及其与碳排放增加的联系，再加上世界范围内化石燃料储量的减少，人们对寻找不会增加二氧化碳浓度且可持续的替代燃料来源产生了巨大的兴趣。一个潜在的来源是使用生物材料，“生物燃料”。一种可能性是使用纤维素制造乙醇或其他燃料，就像巴西使用甘蔗中的糖一样。尽管纤维素非常丰富，但使用纤维素仍存在一些技术挑战，包括将其与细胞壁的其他部分分离，打破其强键结构以及如何使植物产生更多的纤维素。令人惊讶的是，纤维素的巨大重要性与对其形成背后的过程的同等理解并不匹配。我们知道一些组成植物纤维素合成机器的成分，称为纤维素合酶复合物，它存在于细胞表面的脂质膜上，但我们不知道这些成分在机器中的位置，也不知道每个成分是如何帮助制造纤维素的。膜蛋白特别难以研究，因为要使它们溶解，有时需要添加刺激性的洗涤剂，这也会破坏蛋白质之间的相互作用。另一种选择是在使用洗涤剂之前将蛋白质化学交联在一起，但如果大量的蛋白质都结合在一起，这种方法就会变得复杂。为了简化这个问题，我们修改了其中一种蛋白质，这样我们就可以看到蛋白质不同部分形成交联的潜力。通过分别观察每个区域，它可以简化分析，还可以告诉我们不同的蛋白质在哪里相互结合。利用这些信息，我们将了解构成纤维素的整个蛋白质复合物是如何组织的。这一点很重要，因为正是这种复合物的组织结构决定了纤维素微纤维的结构。我们还将使用最近开发的一种技术，使我们能够标记在其天然环境中与纤维素合酶复合物的成分结合或接近的蛋白质。通过将这些结果与研究不同细胞类型的纤维素合成所获得的结果进行比较，将使我们能够帮助区分哪些是制造纤维素所需的基本核心成分，哪些可能只是短暂结合，并且可能参与在细胞周围移动的复合物的定位。最终，这项工作应该提供一个框架，我们可以用它来改变它产生的纤维素的性质。众所周知，一些突变会降低纤维素的结晶度，从而使其更容易分解为可用于生物燃料或其他工业应用的组成糖。这项工作应该为如何做出更大的改进提供重要的信息。

Cellulose is the major component of many plant cells walls and is considered to be the world's most abundant naturally occurring polymer and is a major component of the natural world all around us. Wood is composed of plant cell walls and a particularly high proportion (up to 70%) of wood is made up of cellulose. Cellulose is also important in determining the mechanical properties of crop plants and consequently important in preventing cereals and other crops from falling over (lodging). For industry, the properties of the secondary walls directly determine the properties of the manufactured products, for example paper quality and the fibres used in textiles. Additionally, the pressing need to increase the proportion of our raw materials that are biodegradable can be filled by using natural plant fibres instead of synthetic fibres in materials such as fibreglass. Global warming and its links to rising carbon emissions, due to the use of fossil fuels, such as petrol, coupled with diminishing worldwide fossil fuel reserves has generated a huge interest in finding alternative fuel sources that do not contribute to increases in CO2 concentrations and are sustainable. One potential source is to use biological material, "biofuels". One possibility is to use cellulose to make ethanol or other fuels in the same way that sugar from cane has been used in Brazil. Although cellulose is very abundant there are several technological challenges associated with using cellulose, including separating it from other parts of the cell wall, breaking up its strongly bonded structure and how to get plants to make more cellulose. Surprisingly, the vast importance of cellulose is not matched by an equal understanding of the processes behind its formation. We know some of the components that make up the plant's cellulose synthesising machinery, termed the cellulose synthase complex, which resides in lipid membranes at the cells surface, but we don't understand where in the machinery these components reside nor how each component contributes to making cellulose. Membrane proteins are particularly hard to study as to make them soluble it is sometimes necessary to add harsh detergents that also break up interaction between proteins. One alternative is to chemically crosslink the proteins together before using detergents, but this can become complicated to unravel if large numbers of proteins in complex all become bound together. To simplify this problem we have modified one of the proteins such that we will now be able to look at the potential of different parts of the protein to form crosslinks. By looking at each region separately, it should simplify the analysis and also tells us where different proteins bind to one another. Using this information we will get an idea of how the entire protein complex that makes cellulose is organised. This is important because it is the organisation of this complex that determines the structure of the cellulose microfibril. We will also use a recently-developed technique that allows us to label proteins that bind to, or are close to components of the cellulose synthase complex in their native environment. By comparing these results with those obtained from studying cellulose synthesis in different cell types will enable us to help distinguish what are essential core components required to make cellulose from those that may only bind transiently and may be involved in localisation of the complex of in moving it around the cell.Ultimately this work should provide a framework that we can use to make changes that may alter the properties of the cellulose that it produces. It is already known that some mutations reduce the crystalinity of the cellulose and so makes it easier to breakdown into its constituent sugars that maybe used for biofuel or other industrial applications. This work should provide important information about how to make much more dramatic improvements.