Laboratory of Supramolecular Biology

Bacterial Motility and Signal Transduction Group

Faculty and Research Theme
Michio Homma Professor

Michio Homma (Professor)

Structure and Function of Bacterial Flagella

Ikuro Kawagishi (Associate Professor)

Chemo- and Thermosensory Signal Transduction in Bacteria

Seiji Kojima (Assistant Professor)

Energy Transduction in Bacterial Flagellar Motor

Overview
If you think about bacteria, what comes to mind? Some might say that bacteria are bad organisms that cause infectious diseases, others may say that fermented soy beans (Natto) are made using bacteria. These are true statements, but bacteria are actually very useful in modern life science technology. Such a small organism can move by itself (motility), and can sense environmental information (recognition). Bacteria have the ability to move toward better environments (taxis). Our laboratory is trying to understand how bacteria sense and move at the molecular level.

Mechanism of energy coupling in the flagellar motor
The bacterial flagellum is a helical filament driven by a reversible rotary motor at its base. The energy source for the motor is an electrochemical proton (or sodium ion) gradient across the cytoplasmic membrane. The flagellar filament is a huge organelle, whose length is several times larger than the cell body. This flagellar system is the only rotary locomotive organelle to be described. Interestingly, the mechanism underlying flagellar motor rotation has yet to be fully elucidated. Therefore, we are trying to clarify the energy coupling using the following approaches: (i) Transform proton-driven motors into sodium-driven motors by genetic manipulation, (ii) Precisely measure flagellar rotation using a tiny bead attached to the rotating filament, (iii) Investigate interactions between charged amino acid residues in the rotor and stator, (iv) Determine the protein structure of the motor, and (v) Reconstitute the entire motor in a proteoliposome using purified motor components. With these projects,
Fig. Bacterial flagellar system
we wish to elucidate the workings of this magnificent molecular machine.
Signal transduction in bacteria
Staffs support this group
Bacteria, like human beings, sense and respond to environmental changes. A remarkable example of such bacterial responses to the environment is chemotaxis, i.e. the ability to migrate toward nutrients and away from harmful substances. Indeed, bacteria can sense some chemicals even at extremely low concentrations (nanomolar levels). The sensors for such sensitive detection are proteins called chemoreceptors, and are located in the bacterial cytoplasmic membrane. Each chemoreceptor can detect various stimuli (amino acids, sugars, pH, and temperature) and signals into the cytoplasm. The signals are processed by cytoplasmic signal transduction systems, which consist of several types of proteins and regulate the rotation of the flagellar motor . As a model sensing system, our laboratory studies bacterial chemotaxis signal transduction. We try to understand how the whole system works by orchestrating a variety of components, and focus on the mechanisms of chemoreceptor signaling and motor regulation.
Group Members
References
  1. Hyakutake, A., et al. (2005). J. Bacteriol. 187: 8403-8410.
  2. Sowa, Y., et al. (2005). Nature 437: 916-919.
  3. Shiomi, D., et al. (2005). J. Bacteriol. 187: 7647-7654.
  4. Fukuoka, H., et al. (2005). J. Mol. Biol. 351: 307-317.
  5. Okabe, M., et al. (2005). J. Biol. Chem. 280: 25659-25664.
  6. Yakushi, T., et al. (2005). J. Bacteriol. 187: 778-784.
  7. Homma, M., et al., (2004). Proc. Natl. Acad. Sci. USA 101:3462-3467.
  8. Yakushi, T., et al., (2004). J. Bacteriol. 186: 5281-5291.
  9. Asai, Y., et al., (2003) J. Mol. Biol. 327: 453-463.
  10. Shiomi, D., et al., (2002). J. Biol. Chem. 277: 42325-42333.
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