Date:
February 5, 2020
Source: DOE/Argonne National Laboratory
Summary:
Sunlight and leaves (stock image). Credit: © Elena Volkova
/ Adobe Stock
Plants have been harnessing the sun's energy for hundreds of millions of years.
Algae and photosynthetic bacteria have been doing the same for even longer, all
with remarkable efficiency and resiliency.
It's
no wonder, then, that scientists have long sought to understand exactly how they
do this, hoping to use this knowledge to improve human-made devices such as
solar panels and sensors.
Scientists from the U.S. Department of Energy's (DOE) Argonne National
Laboratory, working closely with collaborators at Washington University in St.
Louis, recently solved a critical part of this age-old mystery, homing in on the
initial, ultrafast events through which photosynthetic proteins capture light
and use it to initiate a series of electron transfer reactions.
"In
order to understand how biology fuels all of its engrained
activities, you must understand electron transfer," said Argonne biophysicist
Philip Laible. "The movement of electrons is crucial: it's how work is
accomplished inside a cell."
In
photosynthetic organisms, these processes begin with the absorption of a photon
of light by pigments localized in proteins.
Each
photon propels an electron across a membrane located inside specialized
compartments within the cell.
"The
separation of charge across a membrane -- and stabilization of it -- is critical
as it generates energy that fuels cell growth," said
Argonne biochemist Deborah Hanson.
The
Argonne and Washington University research team has gained valuable insight on
the initial steps in this process: the electron's journey.
Nearly 35 years ago, when the first structure of these types of complexes was
unveiled, scientists were surprised to discover that after the absorption of
light, the electron transfer processes faced a dilemma: there are two possible
pathways for the electron to travel.
In
nature, plants, algae and photosynthetic bacteria use just one of them -- and
scientists had no idea why. What they did know was that the propulsion of the
electron across the membrane -- effectively harvesting the energy of the photon
-- required multiple steps. Argonne and Washington University scientists have
managed to interfere with each one of them to change the electron's trajectory.
"We've been on this trail for more than three decades, and it is a great
accomplishment that opens up many opportunities," said Dewey Holten, a chemist
at Washington University.
The
scientists' recent article, "Switching sides -- Reengineered primary charge
separation in the bacterial photosynthetic reaction center," published in the
Proceedings of the National Academy of Sciences, shows how they discovered an
engineered version of this protein complex that switched the utilization of the
pathways, enabling the one that was inactive while disabling the other.
"It
is remarkable that we have managed to switch the direction of initial electron
transfer," said Christine Kirmaier, Washington University chemist and project
leader. "In nature, the electron chose one path 100 percent of the time. But
through our efforts, we have been able to make the electron switch to an
alternate path 90 percent of the time. These discoveries pose exciting questions
for future research."
As a
result of their efforts, the scientists are now closer than ever to being able
to design electron transfer systems in which they can send an electron down a
pathway of their choosing.
"This
is important because we are gaining the ability to harness the flow of energy to
understand design principles that will lead to new applications of abiotic
systems," Laible said. "This would allow us to greatly improve the efficiency of
many solar-powered devices, potentially making them far smaller. We have a
tremendous opportunity here to open up completely new disciplines of
light-driven biochemical reactions, ones that haven't been envisioned by nature.
If we can do that, that's huge."
Story
Source:
Materials provided by DOE/Argonne
National Laboratory. Original written by Jo Napolitano. Note: Content may be
edited for style and length.
Journal Reference:
1.
Philip D. Laible, Deborah K. Hanson, James C. Buhrmaster, Gregory A. Tira,
Kaitlyn M. Faries, Dewey Holten, Christine Kirmaier. Switching
sides—Reengineered primary charge separation in the bacterial photosynthetic
reaction center. Proceedings of the National Academy of Sciences, 2020; 117 (2):
865 DOI: 10.1073/pnas.1916119117
Source: Science Daily URL:
https://www.sciencedaily.com/releases/2020/02/200205132347.htm