부산대학교 도서관

We characterized the RecA-CheW protein complex, that allowed the identification of the critical interfaces implied in the interaction and its role in the signaling array assembly. RecA residues Gln20, Arg222, Arg176 and Lys250 that are located in the multi-functional N-terminal and central structural domains of the protein, were described as essential for the interaction. In the case of CheW protein, residues Phe21, Lys55, Asp83 and Phe121 were involved in the RecA-binding, that do not seem to interfere with any other CheW-biding targets. Further, the obtained results demonstrate that the loss of swarming ability when there is an increase of RecA concentration was the consequence of chemosensing array assembly disruption, that previous works have established as essential for swarming in temperate swarmers. Using high resolution microscopy assays we were able to track CheW and RecA protein distribution within the cell during SOS response induction, elucidating the role of the RecA protein in the distribution of CheW and the assembly of chemoreceptor signaling arrays. The obtained results head to the proposal of a model that explains how bacterial cells adapt their surface motility in response to the presence of DNA-damaging agents by sensing them via SOS system induction. During surface colonization, bacterial cells will likely be exposed to a wide range of injurious, and potentially lethal, compounds that are avoided through SOS response induction and consequent swarming ability impairment. When DNA injuries are generated, RecA activates the SOS machinery, and its concentration rises swi􀲏��ly since recA is one of the first genes to be induced in the hierarchy of SOS activation. The increase of intracellular RecA concentration during SOS-response disturbs the equilibrium between this protein and CheW, causing the cessation of swarming. RecA prompts the titration of CheW protein, preventing polar signaling array assembly during SOS response, and thereby inhibiting motility. By this mechanism, bacteria avoid exposure to higher concentrations of the DNA damaging agent, and so, cell death. Following DNA damage repair, RecA concentration returns to its basal level, releasing CheW, that restores chemosensory array assembly, returning the cell to a non-DNA damage motile condition. Therefore, the present work characterizes the molecular mechanisms that govern RecAmediated swarming modulation, by which using RecA as a sensor, Salmonella cells can adapt their surface motility in response to adverse environmental conditions.