Grant: Project Grant

Many bacteria produce long thin hair-like filaments called type IV pili (T4P) on their surfaces. T4P are used by bacteria as grappling hooks to grab onto their hosts, where they colonize appropriate niches (in the case of good bacteria) or cause disease (bad bacteria). T4P filaments can be repeatedly extended and retracted, allowing the bacteria to crawl along surfaces or use them as fishing rods to capture free DNA from the environment, leading to acquisition of new antibiotic resistance genes. The T4P are made by a large multi-component nanomachine that assembles (extends) and disassembles (retracts) the filaments. It does this using highly-conserved molecular motors capable of generating some of the strongest retraction forces ever measured - up to 100,000 x the weight of the bacterial cell. The way in which the T4P motor functions is among the most important unresolved questions in the field. Mutation of critical motor components can cripple the bacteria, suggesting they are good therapeutic targets. In this proposal we will use multiple techniques to solve the three-dimensional structures of the motors from two evolutionarily-distinct types of T4P system to understand how they perform their extension and retraction functions. Combined with the expertise and tools for study of the T4P system we have built over the past 20 years, these structures will guide the generation of specific mutants that will allow us to test our predictions about motor function. As we reveal how the individual components work together, we will use that knowledge to understand how inhibitors of the motors, produced by natural predators of the bacteria, block their function, information that is valuable for the rational design of new therapeutics.