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Michio Homma Professor |
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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
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Overview
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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.
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Mechanism of energy coupling in the flagellar motor
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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,
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| Fig. Bacterial flagellar system |
we wish to elucidate the workings
of this magnificent molecular machine.
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Signal transduction in bacteria
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| 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.
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| Group Members |
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References
- Hyakutake, A., et al. (2005). J. Bacteriol. 187:
8403-8410.
- Sowa, Y., et al. (2005). Nature 437: 916-919.
- Shiomi, D., et al. (2005). J. Bacteriol. 187:
7647-7654.
- Fukuoka, H., et al. (2005). J. Mol. Biol. 351:
307-317.
- Okabe, M., et al. (2005). J. Biol. Chem. 280:
25659-25664.
- Yakushi, T., et al. (2005). J. Bacteriol. 187:
778-784.
- Homma, M., et al., (2004). Proc. Natl. Acad. Sci.
USA 101:3462-3467.
- Yakushi, T., et al., (2004). J. Bacteriol. 186:
5281-5291.
- Asai, Y., et al., (2003) J. Mol. Biol. 327: 453-463.
- Shiomi, D., et al., (2002). J. Biol. Chem. 277:
42325-42333.
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i n d e x |
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 Biological
Rhythm Group (Chronobiology)
Biomembrane Functions Group
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Molecular
Neurobiology Group