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Topic Name: A new insight into the mechanism of photosynthesis
Category: Biodesign
Research persons: Lead author Haiyu Wang, Biodesign Institute; Su Lin, Biodesign Institute; James Allen, ASU Department of Chemistry and Biochemistry; JoAnn Williams, ASU Department of Chemistry and Biochemistry; Sean Blankert and Christa Laser, Biodesign Institute.
Location: The Biodesign Institute,1001 S. McAllister Ave.PO Box 875001,Tempe, AZ 85287-5001, United States
Details
During the remarkable cascade of events of photosynthesis, plants approach
the pinnacle of stinginess by scavenging nearly every photon of available light
energy to produce food. Yet after many years of careful research into its exact
mechanisms, some key questions remain about this fundamental biological process
that supports all life on earth.
Now, a large research team led by Neal Woodbury, a scientist at ASU’s
Biodesign Institute, has come up with a new insight into the mechanism of
photosynthesis, which involves the orchestrated movement of proteins on the
timescale of a millionth of a millionth of a second. Their findings are
described in “Protein Dynamics Control the Kinetics of Initial Electron
Transfer in Photosynthesis,”
in the May 4 issue of Science.
“The studies that led up to this work initiated 20 years ago when Jim Allen
and I looked at one of our mutants and thought our spectrometer
was broken,” Woodbury said. “That mutant turned out to be the first of a
long series of mutations that systematically altered the energy of the initial
reaction.” Since then, Woodbury and colleagues have managed to shed light on
an amazing process that provides earth’s primary power source
The research team includes lead author
Haiyu Wang, Biodesign Institute; Su Lin, Biodesign Institute; James Allen, ASU
Department of Chemistry and Biochemistry; JoAnn Williams, ASU Department of
Chemistry and Biochemistry; Sean Blankert and Christa Laser, Biodesign
Institute.
To get a closer look at what was happening during photosynthesis, the team
used a well studied purple
photosynthetic bacterium called Rhodobacter sphaeroides. This type
of organism was likely one of the earliest photosynthetic bacteria to evolve.
The researchers focused their efforts by studying the center stage of
photosynthesis, the reaction center, where light energy is funneled into
specialized chlorophyll
binding proteins.
The textbook picture of photosynthesis represents the reaction center
proteins as a scaffold, holding chlorophyll molecules at a highly optimized
distance and orientation so that electrons can hop from one chlorophyll to
another. With the chlorophylls in just the right position, any systematic
protein movement was thought to be merely a side product of electrons shuttling
between chlorophyll molecules.
Woodbury and his colleagues tried to uncover more of the physical mechanism
driving photosynthesis by creating mutants that would theoretically tweak the
electron transfer relationships between molecules in the reaction center.
“After years of failure trying to break the system by changing the
energetics, we were left with the nagging question of how it continued to work
so well,” said Woodbury, ASU professor of Chemistry and Biochemistry and
director of Biodesign’s Center for BioOptical Nanotechnology.
The researchers started to inch closer to an answer when Wang, a postdoctoral
research associate in Woodbury’s lab, noticed something in common with all of
the different mutants. When using a new model based on reaction-diffusion
kinetics, Wang saw that the curves representing how fast electrons moved in the
reaction center had a similar shape. “He decided that there must be some sort
of underlying physical principle involved,” Woodbury said.
Not many research groups are equipped to measure the early events in
photosynthesis because of the extremely short timescale –similar to the amount
of time it takes a supercomputer to carry out a single flop. Wang was able to
use the ultrafast laser facility (funded by the National Science Foundation),
which acts like a high-speed motion picture camera that can capture data from
these lightning-fast reactions.
“He tried a really hard experiment, and he was actually able to measure the
protein motion and match it to electron transfer,” Woodbury said. This
discovery helped the researchers understand why changing the energetics didn’t
knock out photosynthesis.
The movement of the reaction center proteins during photosynthesis allows the
plant or bacteria to harness light energy efficiently even if conditions
aren’t optimal. So, while Woodbury and colleagues made it difficult for
photosynthesis to work, the proteins were able to compensate by moving and
energetically guiding the electrons through their biological circuit.
According to Woodbury, the reaction center proteins work for electrons in a
way similar to how a slow moving elevator with no doors would work for people.
The electrons are able to get off at the spot that they need to because the
protein motion adjusts the energetics until it is just right. Even if the
elevator starts a little too high or low (initial energies are not optimal), the
people (electrons) can still get off on the right floor.
This way of representing the electron transfer process successfully captured
the contribution of the protein movements to the rate of the reaction. The
scientists were then able to quantitatively model the effect of the mutations on
the initial rate of photosynthetic electron transfer and answer questions that
had been haunting them for 20 years.
The answers may be good news for the development of organic solar cells,
which have been of commercial interest due to their relatively low cost compared
to traditional silicon solar cells. “Some of the problems that you have with
the organic
photovoltaic arise from the fact that they don’t work under all of the
conditions you want them to,” Woodbury said.
The robustness of the natural system may offer some useful lessons for
engineers trying to improve on current technologies. Woodbury proposed that
there might be a way to increase the flexibility of the system used in organic
solar cells by incorporating solvents that move on a variety of time scales that
could “tune” the molecules to work in a wider variety of conditions.
Woodbury also expects that this new research will help move the study of
photosynthesis forward. “It’s changed the way I look at how photosynthesis
works and has opened up a whole set of new questions,” he said.
“One of the areas that we’re particularly interested in is how the
absorption of light starts protein movement,” Woodbury said. The researchers
are also looking for future experiments to help explain what sort of protein
movements may be occurring in the reaction center and then try to match these
findings with current computer models of protein movement.
About researchers:
Neal Woodbury
Nwoodbury@asu.edu
ASU’s Biodesign Institute
Professor Department of Chemistry & Biochemistry in the College of
Liberal Arts and Sciences
Neal Woodbury, PhD, leads a team that seeks to develop molecular devices and
nanoscale hybrid electronics for use in biomedicine, environmental remediation
and monitoring, threat detection and agriculture. His research into the
structure/function relationships in photosynthesis led him to realize the
awesome potential of harnessing the energy of light to direct chemical
reactions.Looking at the diversity of nature, Dr. Woodbury clearly sees that there must
be a molecular formula in the form of a heteropolymer sequence that has almost
any desired function or property - a molecular cure for disease, a sensor for a
toxin, and a complex molecular matrix for computing or display. One must simply
use the right basis set of chemical monomers and search the sequence space until
an answer is found. His efforts have been directed at building synthetic systems
that can do this: speed up natural evolution.Dr. Woodbury is an advocate of interdisciplinary science as a means of
providing researchers greater vision in addressing real-world problems.Dr.
Woodbury's body of published work includes more than 75 published articles and
studies. He had been a member of the National Science Foundation (NSF)
Biophysics Panel for the past year; a current member of the NSF IGERT Panel; and
an associate editor of Photochemistry and Photobiology. He has served as the
Director of the Photosynthesis Center at ASU and is an active member of the
American Chemical Society, Biophysical Society and American Photobiology
Society.Dr. Woodbury received his B.S. in Biochemistry from the University of
California at Davis and his Ph.D. from the University of Washington
Haiyu Wang
Postdoctoral Research Associate
Lab: Woodbury
(480) 727-0394
Haiyu.wang@asu.edu
Su Lin
slin@asu.edu
Senior Research Specialist, Department of Chemistry and Biochemistry in the
College of Liberal Arts and Sciences
Dr. Su Lin is a senior research specialist at the Ultrafast Laser Facility
for the Department of Chemistry and Biochemistry in the College of Liberal Arts
and Sciences. The Ultrafast Laser Spectroscopy and Imaging Facility is housed in
several laboratories in the department. The facility specializes in the
development and application of time-resolved laser spectroscopy to biological
and chemical research. It provides advanced laser technologies and instruments
for spectroscopic and imaging measurements to observe chemical reactions in real
time with temporal resolution down to FS time scales, spatial resolution, and
sensitivity, to the point where single molecule signals are detectable
Allen J. Bard
ajbard@mail.utexas.edu
Analytical Chemistry
Professor, Faculty
Director, Center for Electrochemistry
Norman Hackerman-Welch Regents Chair
Contact Information
Office-WEL 2.426
Office Phone-471-3761
Lab WEL 2.421, 2.144, 2.102
Lab Phone-471-1323, 471-6890
Fax-471-0088
& JoAnn Williams, ASU Department of Chemistry and Biochemistry; Sean
Blankert and Christa Laser, Biodesign Institute.
Funded :
The Biodesign
Institute’s collaborations include dozens of academic, nonprofit and
for-profit organizations in fields as diverse as health care, technology,
electronics, agrisciences, law enforcement and national security
The Institute benefits substantially from a voter-approved tax supporting
K-12 education and university research in Arizona. ASU has committed a
significant share of these tax-generated funds over the next five years to the
Institute’s research programs to ensure a solid launch for the Institute. The
research must ultimately be self-supporting, with funding from external sources
including government and industry grants and philanthropic support. Many of our
research projects are already self-supporting.
In 2003, the Arizona legislature passed a far-sighted research infrastructure
bill that has further accelerated ASU’s ability to build the Institute. The
first building was completed in December 2004, and a second opened in January
2006.
The Institute is master-planned
as four interconnected buildings with 800,000 sq. ft. of advanced research
space. The first building, which is 172,000 sq. ft., opened in December 2004 and
was funded by ASU. In 2003, the Arizona legislature passed a far-sighted
research infrastructure bill that enabled construction of a similar second
building, opening in January 2006. Flexibility is built into every aspect of the
facilities, so they can rapidly be adapted to changes in technology.
In The Images:
1. Neal Woodbury
2.Biologists have discovered that a
split-second, highly orchestrated process drives photosynthesis.
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