From unicellular organisms to human, biological motion, which is a fundamental function of living system, is driven by complex structures composed of biological macromolecules, such as proteins and nucleic acids. They are called ‘dynamic nanomachine’ and the bacterial flagellum is one of them. The flagellum rotates very fast and controls bacterial motility. The flagellum is an ultra-efficient motor far beyond artificial motors, and constructed through a flexible self-assembly mechanism.
In this research project, we aimed at understanding of the self-assembly mechanism of nano-structure and the ultra-efficient conversion mechanism of extremely small energy through the studies of molecular structure, dynamics and formation of the bacterial flagellum. To analyze the flagellum at nanoscale precision, we developed experimental techniques of X-ray structural analysis, electron cryo-microscopy and optical nano-photometry. We determined the structures of the helical screw, which is the main-body of the flagellum, the universal joint connecting the screw and the drive shaft of the motor, and the flagellar protein export apparatus. We revealed the mechanism of flagellar protein export, which is essential for the flagellar self-assembly, and roles of ATP hydrolyzing energy and proton motive force on the protein export.
This research project was carried out in complementary collaboration with Yale University in US. The Japanese group investigated the structure, function and dynamics of the flagellum, and the US group produced large amount of flagellar component proteins by genetic manipulation and provided various samples for the structural analysis. The highly efficient energy-conversion mechanism of living system reveled by this project must contribute to establish bases of biotechnology towards design and creation of artificial nano-machines in future.