Starch Granule Enzymology

Starch has a central role in the diet of humans as a source of energy from crops such as wheat, maize and rice. Many food products contain starch as a thickening, gelling or pasting agent. Starch also has many industrial uses as a feedstock for biofuels, as a packaging material or as a pharmaceutical ingredient. Although there is a wide natural diversity of starches, many uses require the starch to be modified. In an ideal world, it would be better to grow plant crops that can directly produce the starches with the desired properties. To that end, we intend to better undestand the details of the processes involved in the generation of the highly organised starch granule as a basis for generating new starches in plants.

Decoding Calcium Spiking in Nodulation

Plants require light, water and certain nutrients for growth - not least nitrogen, which is a key component of fertilisers. Leguminous plants, such as peas and beans, fix their own nitrogen from the atmosphere by forming a symbiotic relationship with bacteria that can perform this remarkable biochemistry. The process by which the bacteria form this relationship with the plant involves a complex series of chemical communications, ultimately leading to a specialised organ called the root nodule. An understanding at the atomic level of the key components of the signalling pathway will help in the long term goal of getting non-legumes to fix their own nitrogen to avoid the need for fertilisers.

Oxalate-Degrading Enzymes

We have taken a lead in the discovery of how oxalate-degrading enzymes function in bacteria, fungi and plants. They are involved in the degradation of lignin, in the response to pathogen attack and in the response to acid exposure. These enzymes are members of the vast cupin superfamily of proteins. We now have a deep understanding of the structure-function relationships of these enzymes. So much so, that we have idenfied a rare example of how one enzyme activity could directly evolve into another with a single mutation. This provides insights into how the cupin superfamily could have become so large.

Other Cupin Enzymes

We have discovered a cupin enzyme in pea that could be involved in the establishment of nitrogen-fixing nodules in this leguminous plant. This enzyme produces hydrogen peroxide, a molecule that is important in the remodelling of plant cell walls that is necessary during nodule organ formation. Understanding such processes is important given the need for agriculture to supply many crops with nitrogen.

We have identified a cupin enzyme in a bacterium that is capable of degrading a common plant natural product, quercetin, likely to provide a source of energy for growth of the bacterium. The enzyme is similar to one found in some fungi, but differs in its enzyme cofactor requirement for iron rather than copper. Copper was not available to biology until relatively recently in evolutionary history, so the copper-requiring enzyme probably evolved from the iron enzyme.

Chorismate Synthase

Chorismate synthase is an enzyme of the shikimate metabolic pathway required for the biosynthesis of many compounds that are essential for the growth of plants, bacteria and fungi. Another enzyme of this pathway is the target for the hugely successful herbicide glyphosate that is marketed as Roundup. Chorismate synthase is therefore another potential target for herbicides and anti-microbial drugs. We have discovered a novel catalytic mechanism of this enzyme allowing the potential to develop very selective drugs against this target. We have also identified the mode of action of some known inhibitors that could be developed into drug leads.