Structural and functional investigations on AppA and PpsR

The flavin and haem containing protein AppA from Rhodobacter sphaeroides is unique in its ability to integrate both light signals and oxygen levels for the regulation of gene expression. These individual functions reside on separate domains, which were recently identified as novel flavin and haem binding domains. In order to better understand how these different stimuli affect the interplay with the downstream effector of gene transcription (PpsR), I want to address its interaction with full length AppA or individual functional domains of the photoreceptor under various conditions. These studies will be based on a structural characterisation of AppA, with special attention being paid to the recently identified central haem binding domain, which supposedly is the key player in signal propagation to PpsR for both light and oxygen sensing. In addition, other biophysical methods such as hydrogen/deuterium exchange and transient spectroscopy techniques will complement the structure guided approach for a better understanding of this unusual signalling process. The comprehension of how different stimuli can be integrated by a single protein and the characterisation of how the light signal alters the non-covalent interaction with PpsR will help to appreciate the functioning of this unique signalling protein in particular and photoreceptors in general, respectively.