Structural and functional studies of the torque-generating system of bacterial flagellar motor. (360G-Wellcome-079545_Z_06_Z)

The bacterial flagellar motor is a membrane-embedded molecular machine that rotates helical filaments, providing a propulsive force for bacteria to swim. The stator of the motor contains 8 to 10 circumferentially arranged units thatgenerate a turning force (torque) acting on the FliG ring of the rotor. The rotation is driven by the gradient of hydrogen or sodium (in some bacteria) ions across the cytoplasmic membrane. This research proposal aims to apply a multidisciplinary approach to the fundamental question: what is the molecular mechanism of torque generation, i.e. what are the elementary molecular events that compose the cycle of converting the electrochemical energy of the transmembrane ion gradient into the mechanical energy of the rotor rotation? To address this question, the biophysical and biochemical properties of individual components (MotA and MotB) and domains of the stator unit of the unidirectional motor of Rhodobacter sphaeroides will be investigated in parallel with characterization of the minimal stator unit as a whole, and complemented by structural studies using X-ray and electron crystallography and small angle X-ray and neutron scattering techniques. This work will address the precise role of extramembrane domains in interaction with the peptidoglycan layer, assembly of the stator unit and interaction with FliG, identify the proton pathway and possible mechanisms for the ion selectivity ofthe stator and characterize conformational changes that occur at discrete stages of protons passing through the torque-generating complex. These studiesshould reveal the possible mechanism responsible for the mechanochemical torque generation and allow formulation of a model adequate for further biochemical and physiological testing.