Determining the structure of proteins using
multidimensional NMR, developing technology for protein
molecular array and colloidal particle array based on self-assembly
and decoding DNA using electron microscopes are the research
areas in which Prof. Nagayama has been involved. "It
may sound as if there were no similarities among these
fields, but the basis for my research is physical instrumentation," says
Prof. Nagayama, who developed a complex observation scheme
that is one of the most powerful methodology in physical
instrumentation.
"Optical image analysis using complex functions is
a miracle because any information obtainable from optical
objects can be completely retrieved. We can usually see
only amplitude images which are a part of the information
obtainable from optical objects," says Prof. Nagayama.
The information that usually cannot be seen involves wave
phase. In 1999, he proposed a complex observation scheme
in order to obtain wave phase information, and two years
later, he proved his concept by developing a phase contrast
electron microscope.
A phase contrast electron microscope has various observation
methods due to the phase plates set at the back focal plane
(BFP). Prof.
Nagayama developed two phase contrast methods. One is a
Zernike phase- contrast method and the other is a differential
interference contrast method called Hilbert differential
contrast method. He says, "Although living organisms
are generally transparent to an electron wave, the electron
wave always changes its phase when scattered by an object.
Living organisms can be observed if phase contrast is obtained
through the scattering wave whose phase is manipulated
by a phase plate." The highest-contrast images ever
were produced by applying a quarter wave phase shift to
all of the scattering waves in the Zernike phase- contrast
method and applying a half wave phase shift exclusively
to scattering waves transferring through a partial frequency
space such as a positive frequency space. An object's optical
information can be reconstructed by combining phase images
and an amplitude image that was obtained by a conventional
method using only an aperture, and it is this complex observation
scheme that Prof. Nagayama developed.
What Prof. Nagayama has been trying to observe using phase
contrast electron microscopes is membrane proteins, which
are hard to crystallize. He says, "We can observe
a single protein, and so, we have taken on the challenge
to do experiments with single proteins."
In 2003, he was able to analyze the structure of a human
ion channel using an phase contrast electron microscope
with 30 A (angstrom) resolution. His goal was to establish
bioelectronics using two- dimensional crystals of protein
molecules when he began research on self-assembly in proteins.
He says, "I would like to relate electric signals
to chemical reactions, for which the most suitable object
is a kind of membrane proteins, channel." The development
of phase contrast electron microscopes encouraged him to
try to achieve his goal again.
Another goal has been to produce a "terabase sequencer" which
can determine the sequence of a single molecular DNA using
a phase contrast electron microscope. With a terabase sequencer,
four kinds of bases, which are complimentarily bound to
DNA, are synthesized to each of which a specific metal
cluster is attached as a label. The labeled bases are then
bound to single-strand DNA and analyzed with an electron
microscope. If the terabase sequencer is built, a sequence
of one billion base pairs can be decoded in just one day.
It will perform the analysis 1,000 times faster than any
conventional system, and thus, the cost of decoding human
DNA would be only about 3,000,000 yen, which is a thousandth
of what currently costs.
When Prof. Nagayama was a graduate student, a DNA decoding
method using an electron microscope was studied in a biophysics
lab of which he was a member. However, chemical decomposition
methods, such as the Sanger method and the Maxam-Gilbert
method, were developed before his group could develop its
own method. He says, "I was shocked because I was
going to start a new field in biology with physical instrumentation.
In biology, physics may always fall behind chemistry.
I felt defeated." His interest shifted to other fields
of research.
However, because the resolution of current electron microscopes
is under 1 A (angstrom) in materials science, it should
be possible to decode DNA using an electron microscope.
He felt encouraged to try decoding DNA again. He says, "I
have to win in this field otherwise I cannot die. So that's
why I came back to this field."
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/045a.html
