Investigating the Function and the Interaction Network of the Flagellar Regulator ATPase FlhG
Motility plays a key role for the superior survival strategy of many bacteria. Sophisticated, macromolecular machines, called flagella, serve as bacterial locomotion organelles. These flagella appear in distinct spatial arrangements along the bacterial cell, constituting the flagellation patterns, w...
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|Zusammenfassung:||Motility plays a key role for the superior survival strategy of many bacteria. Sophisticated, macromolecular machines, called flagella, serve as bacterial locomotion organelles. These flagella appear in distinct spatial arrangements along the bacterial cell, constituting the flagellation patterns, whose disruption is detrimental to motility. However, the number of flagellation patterns that have arisen in a plethora of bacterial species can be counted by the fingers of one hand. How these patterns are established in the first place, and how they are maintained during cell division, remains a yet unassessed task in the field. Two nucleotide-binding proteins, FlhF and FlhG, were identified to be crucial for the spatial regulation of flagella in most flagellated bacteria, which exhibit various flagellation patterns. This work presents a structural and biochemical characterization of the flagella regulating ATPase FlhG, which revealed its function as a molecular switch, having a dimeric, membrane-associated state and a mobile, monomeric state in the cytoplasm. This hallmark feature of MinD/ParA ATPases is conserved in FlhG of peritrichous B. subtilis as well as monotrichous S. putrefaciens. In both organisms FlhG interacts with the flagellar C-ring components FliM and FliN(Y) providing insight into its role as a flagellar C-ring assembly factor, coordinating the assembly of a FliM/FliN(Y) complex to FliG. Differences in the regulatory networks underlying different flagellation patterns were identified in species-specific interaction partners of FlhG, such as the flagellar master regulator FlrA in S. putrefaciens or the late divisome component GpsB in B. subtilis. These findings led to the hypothesis that the spatial arrangement of flagella is encoded in the structure of the interaction network of FlhF and FlhG. This hypothesis is supported by the occurrence of varying C-ring components in differently flagellated bacteria. This work also includes the implementation and successful application of 1H/2H exchange mass spectrometry in Marburg. Not only does this powerful tool allow the convenient investigation of protein dynamics, but also the rapid mapping of protein-protein and protein-ligand interfaces. Interface mapping, in particular, revealed the power of this method and was applied in various research projects.|