Structural and functional studies on the transcriptional regulation of flagellar motility and biofilm formation
Part 1: Numerical regulation in the monotrichous bacterium Shewanella putrefaciens Microorganisms have the ability to adapt to changing environmental conditinos. This has enabled them to colonize virtually nearly every niche on the planet Earth. Key to this ability is bacterial motility, which allo...
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|Summary:||Part 1: Numerical regulation in the monotrichous bacterium Shewanella putrefaciens Microorganisms have the ability to adapt to changing environmental conditinos. This has enabled them to colonize virtually nearly every niche on the planet Earth. Key to this ability is bacterial motility, which allows bacteria to move away from unfavourable conditions and to move towards favourable conditions. In connection with a sensory system, which detects chemical cues and other stimuli, bacteria can move towards nutrients. Bacterial motility is largely enabled by flagella. The biogenesis of a flagellum is a very costly process, which is for this reason highly regulated. In the monotrichous bacterium Shewanella putrefaciens, FlhF and FlhG are responsible for maintaining number and location of the single polar flagellum. In the course of this work, it could be shown that FlhG limits the number of flagella to one by directly interacting with the master transcriptional regulator of the flagellum, FlrA. Furthermore, FlhG is implicated in assembly of the cytosolic face of the flagellum, the C-Ring. The transcriptional control via FlrA as well as the C-Ring assembly via FliM occur through the same binding site on FlhG. This highlights the central role of FlhG and shows that FlhG integrates the two processes to regulate flagellar number. Taken together, these observations represent an important step towards a complete conceptual description of flagellar biogenesis. Thereby, these results also form the basis for further research. Part 2: Transcriptional regulation of biofilms is mediated by RemA, which interacts with DNA in a histone-like manner Instead of a motile lifestyle, bacteria can also establish a multicellular, sessile lifestyle in the form of biofilms. In biofilms, bacterial cells establish a division of labour and establish an increased resistance against antibiotics and environmental hazardous conditions. This is mediated by the secretion of extracellular proteins and other biological molecules. The protein RemA is central to this process, as it activates the secretion of these extracellular components. Furthermore, RemA is implicated in processes which enable a cellular protection against osmotic pressure, which occurs during biofilm formation. In the context of this work, the structure of RemA from Geobacillus thermodenitrificans could be elucidated. RemA interacts with DNA in a novel and unique way, which is reminiscent of DNA-looping by histone-complexes. By means of biochemical methods, crucial residues of RemA responsible for DNA interaction could be functionally investigated. Furthermore, the structural fate of amino acid mutations, which impair the functionality of RemA, could be investigated. Taken together, this work represents an important step towards the understanding of the transcriptional processes that govern biofilm-formation and osmoprotection in Bacillus subtilis. This work also provides the basis to further investigate the function of RemA in the cellular context. In the future, the structural investigation of RemA-DNA-interaction is facilitated by the insights obtained in the context of this work. Part 3: Membrane protein biogenesis is regulated by a structurally unique, co-translational state of FtsY. Membrane proteins are translated by ribosomes and predominantly inserted into the membrane by the SecYEG-translocon. A factor critical for this process is the SRP-receptor FtsY, which enables co-translational targeting to the translocon in coopration with the SRP-particle FFH and SRP-RNA. In the context of this work it could be shown that a co-translational state of FtsY, the helical domain N2-4, critically mediates membrane targeting of the receptor. By means of crystallographic analyses and studies in solution, it could be shown that the subdomain of N2-4 possesses a different fold when isolated than in the context of the G-domain of FtsY. This observation represents a unique paradigm, which indicates that nascent N2-4 executes a different function during its own translation than when N2-4 is part of the mature FtsY-receptor. These results are an important step towards the conceptual understanding of membrane protein biogenesis and –targeting. Further work could elucidate, whether this concept also applies to homologs of FtsY such as FlhF.|
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