| Bacteria swim by means of one or more rotating flagella. The bacterial flagellum is a large macromolecular structure assembled from multiple copies of more than 18 proteins. It is rotated by a rotary motor in the cytoplasmic membrane. Motor function is directly coupled to the flow of protons through membrane spanning channels, which are part of the stator of the motor. The motor is located in the cytoplasmic membrane and extends into the cytoplasm. The motor or basal body is isolated as complex with the hook with a mass of about 15.8 million daltons. It is a structure made of a series of rotationally symmetric rings which form the rotor and a set of bushings allowing torque to be transmitted to the filament.;Image analysis of electron micrographs of specimens preserved in vitreous ice has been used to determine the structure of the flagellar motor with the cytoplasmic components intact. Structures of basal bodies with components selectively removed have been compared to determine the locations of proteins involved in assembly and torque generation. The symmetry of the cytoplasmic components has been solved and suggests a symmetry mismatch is involved in torque generation. The structures of basal bodies from two gene fusion mutants, one a full length fusion protein, the other with a large deletion have been analyzed. The location of subunit interactions critical to motor function have been deduced from these results.;A novel approach to solving dime dimensional structures with mixed symmetries, which combines helical analysis and single particle methods of image analysis, has been developed and shown to be promising. An improved structure of the hook was determined to demonstrate the correctness of the method. Though he symmetry of all rings can not yet be determined, the method correctly determines the structure of the hook. It has shown that there is a channel running the length of the hook, rod and motor which is closed in the cytoplasmic membrane. The hook-rod transition can be clearly observed. The rod is a helical structure with a lattice similar to the hook and filament. |
