The role of acylation in cellulose synthesis

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Cellulose is the major component of many plant cells walls and is considered to be the world's most abundant naturally occurring polymer. Cellulose is actually composed on many chains of the sugar (glucose) units bonded together to form something known as the microfibril. These microfibrils have unique physical properties that are exploited by plants. Cellulose microfibrils are ubiquitous among higher plants where they are important in determining how plant cells grow and also determining how strong the plant material is. We already exploit the properties of cellulose to make paper and cotton, however, cellulose has the potential to be used in a wide range of other applications including novel materials and as a renewable source of sugars for the production of biofuels and chemicals. One of the major advantages of using plant based material is that plants obtain their carbon from the atmosphere in form of CO2 and so using plant material such as cellulose is not only renewable, but dramatically reduces net carbon emission into the atmosphere compared to the use of fossil fuels. Cellulose is synthesis by a unique enzyme complex that sits in the plasma membrane that surrounds the contents of every cell. Each cellulose synthase complex makes around 18 chains that bond together to form a microfibril. These microfibrils are rigid structures and so as the complex adds sugars to the growing chains, it is effectively driven along the plasma membrane. Given the large size of the complex, it will cause severe local disruption of the plasma membrane. The plasma membrane is composed of lipids that provide a fluid environment that allows movement of the cellulose synthase complex, but it is essential the cells maintain the integrity of the plasma membrane for its viability. Movement of the cellulose synthase complex is governed by long tubular structures known as microtubules that sit close to the plasma membrane and guide the movement of cellulose synthase complex and hence orientation of the cellulose microfibrils. Orientation of cellulose microfibrils is essential for the growth of plant cells and has a major influence on their physical properties.Although cellulose is very abundant, there are several technological challenges associated with studying cellulose, including separating it from other parts of the cell wall and breaking up its strongly bonded structure. Surprisingly, the vast importance of cellulose is not matched by our understanding of the processes behind its formation. We have become interested in how the individual components of the cellulose synthase complex are modified by the addition of fatty acid groups. These fatty acid groups are very hydrophobic and have a very high affinity for membranes. We believe this has an essential role in locking the cellulose synthase complex into the plasma membrane and preventing it "popping out" as the complex moves through the membrane. The cells are also faced with another logistical problem, as the plasma membrane is crowded with many other components. We now want to look at how the plasma membrane might be partitioned to allow unimpeded movement of the cellulose synthase complex. We will investigate how the addition of hydrophobic fatty acid groups both to the cellulose synthase complex and to the underlying microtubules contributes their co-localisation and the ability of the cell to form membrane partitions at sites of cellulose synthesis.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 make it easier to breakdown into its constituent sugars that maybe used for biofuels or other industrial applications. It is likely that a better understanding of the local environment in which plants make cellulose may help us to alter other cellulose properties such as microfibril length.