The Wbl proteins - a novel family of [4Fe-4S] cluster-containing transcription factors

The harmless soil bacteria called streptomycetes are important to our welfare because they are the source of the vast majority of antibiotics used to cure infectious diseases, as well as providing us with numerous other medicines used, for example, to treat cancer, and to help organ transplant patients. We have identified two key regulators (called 'transcription factors') that switch the genetic machinery of these useful bacteria to allow them to reproduce themselves. We have discovered that these regulators are unusual in containing a special sensing device (called an 'iron-sulphur cluster') which likely controls reproduction of the bacteria in response to key environmental signals, like oxygen. In this grant we expect to find out exactly how these regulators work, to understand what they do in the cell and the role of the special sensing device (the 'iron-sulphur cluster'). We also know that similar key regulators are present in dangerous bacteria that cause important fatal diseases like tuberculosis and diphtheria. In the bacterium that causes tuberculosis, one of these regulators controls resistance to a wide range of antibiotics (a phenomenon called 'multi-drug resistance'). If we can understand how these regulators worked, we may be able to develop new medicines to target and eliminate multi-drug resistance, making it much easier to cure patients suffering from tuberculosis.

This grant seeks to understand the biological roles and regulation of a novel class of transcription factors that we have recently discovered carry a redox-active [4Fe-4S] cluster. The Wbl (WhiB-like) family of transcription factors is present throughout the actinomycetes, the family of bacteria that includes Streptomyces, the genus responsible for the production of two-thirds of the known antibiotics, as well as medically important pathogens such as Mycobacterium tuberculosis and Corynebacterium diphtheriae. Classical genetics has shown that Wbl proteins play pivotal and diverse roles in actinomycete biology. Two of the Wbl proteins that are the focus of attention in this grant are WhiB and WhiD, required, respectively, for the early and late stages of sporulation in Streptomyces coelicolor. The third is a remarkable and unique protein called WblP, which is an ECF sigma factor carrying a Wbl domain at its N-terminus. The [4Fe-4S] clusters of WhiD, WhiB and WblP are redox active, suggesting that their transcriptional activity, and hence the expression of the genes under their control, might be redox-regulated in vivo. Importantly, these experiments raise the possibility that Streptomyces sporulation might be redox-regulated, a totally novel and unexpected finding. To address these intriguing questions, we will identify the genes under control of these proteins, establish in vitro assays for their function, and investigate how the nature and redox state of the Fe-S cluster contributes to the biological function of Wbl proteins.