Control of genomic integrity and virulence of Aspergillus fumigatus by ADP-ribosylation.

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Despite their ability to cause serious life-threatening illnesses, the major impact of fungi upon human health world-wide is often overlooked. However, fungal infections kill more people than malaria or tuberculosis. Aspergillus fumigatus, a common mould that we inhale every day, is a primary source of human disease. The threat of life-threatening fungal infections is rising with the increase in the vulnerable patient population and the appearance of drug resistant Aspergillus fumigatus variants. To overcome this problem and develop new treatment strategies, we must understand how Aspergillus can survive in a patient's body.The human immune system combats fungal infections partly by damaging the DNA of the invasive pathogen, thus severely restricting the microbe's ability to survive within the body. Therefore, disease-causing microbes have developed a sophisticated DNA repair machinery to survive in their hosts. However, in fungal pathogens, the mechanisms by which damaged DNA is recognised, the repair factors recruited, and a genomic catastrophe avoided are not well understood. My work focuses on a cellular signal termed ADP-ribosylation, which marks locations of DNA damage and attracts the repair machinery. By studying this signal, my work will provide invaluable insights into how Aspergillus defends itself against the host, potentially enabling us to design new therapies to treat drug-resistant fungi.Based on strong data, my hypothesis is that ADP-ribosylation is a crucial signal that coordinates the response to, and repair of, DNA damage. However, we do not currently understand 1) how the signal is generated in response to the DNA damage, 2) how it coordinates the repair machinery assembly, or 3) whether the signal is required to survive in the host. To address this, I will answer the following questions:1) What do the relevant signalling proteins look like? Seeing the 3D structure of these signalling proteins will help us understand how they work. This is challenging, because these proteins are about one million times smaller than a grain of rice. I will overcome this challenge by using a well-established technique called X-ray crystallography. This allows us - with the help of sophisticated computer software - to determine the 3D structure of target proteins from the patterns of light veering off a crystalline sample. Understanding the workings of the signalling proteins will help us address questions of how they function within fungal cells and in the future enable us to design novel drugs to treat infections.2) How does ADP-ribosylation regulate DNA repair? Since both DNA integrity and ADP-ribosylation signalling are essential for fungal survival, we must be able to control both at specific times within cells. To achieve this, I will use state-of-the-art techniques utilising light to induce DNA damage or remove proteins. I will then compare fungi with and without the ability to signal, asking questions like: Can repair happen without the signal? How does the fungus react to a constant state of emergency due to an inability to remove the signal after the repair? Does ADP-ribosylation signalling differ for different types of DNA damage?3) How does ADP-ribosylation support fungal survival in the host? The interplay of a microbe with its host is extremely complex, and thus insights gained from studying fungi outside the host cannot always explain what occurs during an infection. Therefore, I will use culturable immune cells and animal models, which have an infection response comparable to humans, to understand at which stages of infection ADP-ribosylation signalling is active and whether impairing it has beneficial outcomes for the host.Overall, this study will bring exciting new insights into fungal DNA repair, thus helping us to understand how these dangerous pathogens overcome a crucial aspect of host defence. This is likely to lead to new therapeutic strategies to combat life-threatening fungal infections.