Mechanical Regulation of Ultra-Sensitivity in E. coli Flagellar Motors
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PROJECT Swarming motility, exhibited by many motile species of bacteria, has been implicated in the rapid invasionof hosts during urinary tract infections (UTIs). Annually, UTIs result in several thousand deaths in the US aloneand represent a significant load on the public healthcare system. Swarming motility is substrate-associated andis driven by bacterial flagellar motors that rotate extracellular, helical filaments to generate thrust on the cell-body. Although chemotaxis is not required for swarming, the functioning of a molecular switch that enablesreversals in the direction of motor-rotation is indispensable. The switch is activated by CheY-P, an intracellularresponse-regulator that is regulated by the chemotaxis network. Upon CheY-P-binding, cooperativeinteractions within the multi-subunit switch-complex drive concerted transitions from counterclockwise (CCW)to clockwise (CW) conformations with increasing likelihood, resulting in changes in the direction of rotation. Ourrecent results indicate that flagellar motors sense mechanical forces, arising from contact with solid substrates,and that leads to the inhibition of switching. In a short time the motor adapts to these forces and recovers theability to reverse directions. However, the molecular underpinnings responsible for adaptation remain unclear.Thus, there is a critical need to determine how the switch adapts to mechanical stimuli to promote swarming.Without such knowledge, the potential to capitalize on antivirulence strategies as therapeutic approaches tocombat swarming-mediated host-invasion and antibiotic resistance will likely remain limited. Our long-term goalis to contribute toward the development of new clinically useful antivirulence strategies that target bacterialswarming and colonization. Our overall objective in this application is to determine the molecular mechanismswhereby the switch adapts perfectly to mechanical signals and promotes swarming. Our central hypothesis isthat motor-mechanosensing (sensing of mechanical signals) results in the tuning of ultra-sensitivity through themodulation of allosteric and cooperative interactions within the switch. The rationale for the proposed work isthat a determination of the mechanism of mechanical control of ultra-sensitivity is likely to provide a conceptualframework for the development of strategies to interfere with switch adaptation, and to mitigate swarming. Atthe completion of the proposed research, it is our expectation to have quantitatively explained the mechanismsunderlying switch-adaptation and modulation of ultra-sensitivity by mechanical forces. Results are expected tohave an important positive impact because a detailed understanding of switching near substrates will provide astrong foundation for novel substrate-design in biomedical devices, including catheters, which will target themotor-switch to inhibit swarming.