Dokument

Summary:
Bacteria rely on different motility mechanisms to explore their surroundings and interact with them. Key forms of motility, swimming and swarming, are dependent on a complex macromolecular system called the flagellum, which functions as a rotating molecular motor. This structure is highly relevant for a variety of processes that involve bacterial cells, such as biofilm formation, pathogenesis and chemotaxis. The primary focus of this thesis is the flagellar system of the model organism Shewanella putrefaciens CN-32, which possesses a single primary polar flagellum. To further delineate how the flagellum is assembled and positioned, the interactions of two highly conserved proteins were investigated. These proteins are the MinD-like ATPase FlhG, and the flagellar secretion system component FlhB. This work has demonstrated that FlhG functions as a switch in the assembly of the flagellar C-ring. It is capable of binding, through an overlapping binding site, both the C-ring component FliM, as well as the transcriptional regulator FlrA. The switching of interaction partners depends on the dimerization state of FlhG, and the presence of the nucleotide ATP. FlrA interacts strictly with dimeric, ATP-bound FlhG. Upon binding of FlhG, FlrA can no longer act as a transcriptional activator, and the production of flagellar building blocks is halted. Furthermore, it has been demonstrated that a lack of interaction between FlhG and FlrA in vivo results in hyperflagellation. Additionally, this work shows the structural characterization of the polar FlhB with the help of X-ray crystallography, and identifies a new C-terminal motif, termed the Proline-Rich Region (PRR). A removal of this region results in a decrease in flagellar filament and hook formation in vivo. With the help of further in vitro experiments involving FlhB, FliM was for the first time identified as a binding partner.

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