On Type-4 Pilus Genetics and the Motor ATPase PilB

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The protein filament known as a pilus protrudes from and extends beyond a bacterial cell. One end of the pilus is anchored to the bacterium and the other end is free to attach to living or inanimate surfaces. Such attachments are important for the survival and proliferation of bacteria in the environment where they frequently form microbial assemblages or biofilms. The presence and the biological activities of bacterial biofilms drastically alter (in advantageous or deleterious ways) the biological as well as the physical and chemical properties of their surroundings. One type of bacterial pilus, the type-4 pilus, is able to retract at its base once its distal end is attached to a suitable adhesion point on a solid surface. Many bacteria use type-4 pilus retraction as a motor to move themselves and to reach new resources and colonize new surfaces. This research will investigate the type-4 pilus motor including the molecular mechanisms of its conversion of chemical energy to mechanical work and can lead to new design principles for nanoscale motors. This project will provide interdisciplinary research and educational training at the intersection of biology, physics, and engineering to students (including members of groups underrepresented in science) at both the graduate and undergraduate levels. The retractable type-4 pilus in gram-negative bacteria is the strongest biological motor currently known, capable of generating a stall force of 150 piconewtons. Yet the inner workings of the type-4 pilus remain largely an enigma. This project employs a multidisciplinary approach to study the type-4 pilus motor and its motor ATPase PilB. The genetics of type-4 pilus assembly and disassembly will be investigated using well-defined mutations in Myxococcus xanthus; the structure of PilB will be determined (by X-ray crystallography) at an atomic resolution. Completion of this project will clarify the genetics of T4P extension and retraction and elucidate the mechanism of type-4 pilus assembly catalyzed by the PilB ATPase.