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| FAX |
+81-774-98-2575 |
| Postal Mail Address |
Protonic NanoMachine
Project, ERATO,
JST 3-4 Hikaridai, Seika, Kyoto 619-0237
Japan |
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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. |
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| 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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