Toshio Yanagida
Single Molecule Process Project, ICORP\#,
JST and Department of Physiology \&
Biosignaling, Osaka University Medical School
2-2, Yamadaoka, Suita, Osaka, 565-0871, Japan
Biomolecules assemble to form molecular machines
such as molecular motors, cell signal processors,
DNA transcription processors and protein
synthesizers to fulfill their functions.
Their collaboration allows the activity of
biological systems. The reactions and behaviors
of molecular machines vary flexibly while
responding to their surroundings. This flexibility
is essential for biological organisms. The
underlying mechanism of molecular machines
is not as simple as that expected from analogy
with man-made machines. Since molecular machines
are only nanometers in size and has a flexible
structure, it is very prone to thermal agitation.
Furthermore, the input energy level is not
much difference from average thermal energy,
kBT. Molecular machines can thus operate
under the strong influence of this thermal
noise, with a high efficiency of energy conversion.
They would not overcome thermal noise but
effectively use it for their functions. This
is in sharp contrast to man-made machines
that operate at energies much higher than
the thermal noise. In recent years, the single
molecule detection (SMD) techniques have
rapidly been expanding to include a wide
range of life science. The dynamic properties
of biomolecules and the unique operations
of molecular machines, which were previously
hidden in averaged ensemble measurements,
have now been unveiled. The aim of our research
is to approach the engineering principle
of adaptive biological system by uncovering
the unique operation of biological molecular
machines. We survey our SMD experiments designed
to investigate several molecular machines
and discuss the flexible mechanism of motion
underlying molecular motors, on which SMD
has been most successfully used.