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Name |
Email |
Telephone |
| Professor |
NAMBA, Keiichi, Ph.D. |
 |
+81-6-6879-4625 |
| Associate Prof. |
IMADA, Katsumi, Ph.D. |
 |
+81-6-6879-4625 |
| Assistant Prof. |
MINAMINO, Tohru, Ph.D |
 |
+81-6-6879-4625 |
| Assistant Prof. |
KATO, Takayuki |
 |
+81-6-6879-4625 |
| Assistant Prof. |
KUBORI, Tomoko, Ph.D. |
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+81-6-6879-8361 |
Protonic NanoMachine Group aims at the ultimate
understanding of the mechanisms of self-assembly and its regulation,
conformational switching, force generation, and energy transduction
by biological macromolecular complexes. By convergence of complementary
techniques, such as X-ray diffraction and electron cryomicroscopy
for high-resolution analysis of three-dimensional structures,
and optical and electronic measurements on individual molecular
complexes for analyzing their dynamic behaviors, we try to reveal
the basic principles behind their functional mechanisms, in the
hope that they will become a basis for artificial nanomachine
design and nanotechnology.
| 1 |
Mechanism of self-assembly
and its regulation |
| The bacterial flagellum, a motile organelle,
for example, is a huge protein complex made of about
25 proteins, each of which forms either a ring or rod-like
structure with a range of subunit copy numbers from
a few to few tens of thousands. The whole structure
spans from the cytoplasmic face of the cell membrane
to the extra-cellular space, where the helical filament
grows up to around 15 micrometer. The assembly proceeds
one part after another from the base to the tip in
an efficient and well-regulated manner. We try to reveal
the regulatory mechanisms based on the structure and
folding dynamics of individual component proteins and
sub-complexes. |
| 2 |
Mechanism of conformational
switching |
| Quick reversal of the flagellar motor rotation
and polymorphic switching of the flagellar filament
between left- and right-handed helical forms switch
the direction of cell swimming. The universal joint
function of the flagellar hook is essential in transmitting
the torque to the long helical filament that could
be oriented in various directions. All these processes
involve highly precise and cooperative switching in
the subunit protein conformation coupled with switching
in the interactions with other protein subunits. We
try to visualize these conformational switching and
understand the mechanisms of mechanical signal transduction
based on the structure and dynamics. |
| 3 |
Torque generation mechanism |
| The flagellar motors are only 30 to 40 nm
in diameter, and yet, they rotate as fast as 20,000
to 100,000 rpm. We try to understand the mechanism
of torque generation by studying the three-dimensional
structure and dynamic behavior of its rotation at high
spatial and temporal resolution. |
| 4 |
Energy transduction
mechanism |
| The high-speed rotation of the
flagellar motor is powered by the flow of protons or
Na ions through a membrane channel protein complex
that performs the stator function of the flagellar
motor. The proton or ion flow is driven by the proton
or ion motive force across the cytoplasmic membrane,
and the current amounts only to several tens femtoampere.
We try to measure this extremely small electric current
precisely to obtain clues to the energy transduction
mechanism. |
|
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| 5 |
Protein export mechanism |
| The assembly of the flagellar
axial structure with tens of thousands of protein subunits
always occurs at the distal end of the growing flagellum.
The component proteins are selectively exported from
the cytoplasm into the narrow central channel of the
flagellum by a protein complex attached on the cytoplasmic
face of the motor. This flagellar protein export apparatus
uses the energy of ATP hydrolysis and is highly homologous
to the type III protein secretion system of pathogenic
bacteria, by which pathogenic effecter proteins are
secreted into host cells. We try to visualize the export
process by single molecule technique and understand
the mechanism of selective export based on the structure. |
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| 6 |
Design principles for
protein nanomachine |
| Protein nanomachines have
a unique and special ability to form three-dimensional
structures and large complexes so that individual atoms
take well-defined three-dimensional positions to perform
specific and yet various functions in a highly precise
manner. This ability of self-organization is a great
advantage in nanotechnology development, because, without
this feature, mass production of nanomachines is impossible
and therefore practical applications cannot be expected
no matter how useful individually made nanomachines
could be. The outcome of our studies on protein nanomachines,
which work flexibly and precisely at the same time,
is expected to produce much useful knowledge to eventually
form a basis for design principles for artificial nanomachines
of practical use. |
 
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