MS04-P07 Structural basis for transcriptional control of flagellum assembly by the FliD-FliT complex Hyung Ho Lee (Department of Chemistry, Seoul National University, Seoul, Korea South)email: lee.hyungho@gmail.comDuring the stages of the flagellar assembly process, the flagellar genes are expressed in response to morphological development of flagellar assembly. Flagellar biogenesis is controlled by a negative feedback loop. When FliD was secreted at the late step of flagellar assembly, the FliD-FliT complex disassembled and free FliT bound to the FlhDC complex, a master regulator of flagellar biogenesis, subsequently inhibiting the overall expression of flagellar proteins. Thus, the overall production of flagellar proteins is reduced by sensing flagellar morphology via FliD-FliT complex. In this study, we analyzed the role of the FliD C-terminal domain in pentamer formation and interaction with FliT. We determined the crystal structure of C-terminal domain of FliD bound to FliT, and showed that the FliD Leu443, which is part of the hydrophobic core of the FliD-FliT complex, plays a crucial role in the pentameric oligomerization of FliD. When the FliD Leu443 was mutated, the binding affinity between FliD and FliT was significantly reduced, and it exists as a monomer in solution. Consistently, lengths of flagella in each cell were significantly reduced in L443R mutant strain, suggesting that normal flagellar biogenesis was impeded. These results suggest that the C-terminal domain of FliD plays a crucial role in the pentameric oligmerization of FliD and the binding of FliT to the C-terminal domain of FliD is critical to inhibit the premature assembly of the FliD pentamer in the cytosol.References:

[1] Kim H. MJ.; Yoo, W.; Jin, K. S.; Ryu, S.; Lee, H. H. The role of the FliD C-terminal domain in pentamer formation and interaction with FliT. Scientific Reports. 2017. 7, 4418
Keywords: Flagellum, FliD, FliT