Corporate Banner
Satellite Banner
Scientific Community
Become a Member | Sign in
Home>News>This Article

A New Way of Looking at Photosynthesis

Published: Tuesday, June 12, 2012
Last Updated: Tuesday, June 12, 2012
Bookmark and Share
Future prospects for clean, green, renewable energy may hinge upon our ability to mimic and improve upon photosynthesis.

An artificial version of photosynthesis, for example, could use sunlight to produce liquid fuels from nothing more than carbon dioxide and water. First, however, scientists need a better understanding of how a large complex of proteins, called photosystem II, is able to split water molecules into oxygen, electrons and hydrogen ions (protons). A new road to reaching this understanding has now been opened by an international team of researchers, led by scientists at the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and SLAC National Accelerator Laboratory.

Using ultrafast, intensely bright pulses of X-rays from SLAC's Linac Coherent Light Source (LCLS), the research team produced the first ever images at room temperature of microcrystals of the photosystem II complex. Previous imaging studies, using X-rays generated via synchrotron radiation sources, required cryogenic freezing, which alters the samples. Also, to catalyze its reactions, photosystem II relies upon an enzyme that contains a manganese-calcium cluster that is highly sensitive to radiation. With the high-intensity femtosecond X-ray pulses of the LCLS, the research team was able to record intact images of these clusters before the radiation destroyed them.

"We have demonstrated that the ‘probe before destroy' strategy of the LCLS is successful even for the highly-sensitive oxygen bridged manganese-calcium cluster in photosystem II at room temperature," says Vittal Yachandra, a chemist with Berkeley Lab's Physical Biosciences Division. "This is an important step toward future studies for resolving the composition and atomic structure of the manganese-calcium cluster in the photosystem II complex during the critical formation of oxygen molecules."

For more than two billion years, nature has employed photosynthesis to oxidize water into molecular oxygen. Photosystem II, the only known biological system that can harness visible light for the photooxidation of water, produces most of the oxygen in Earth's atmosphere through a five-step catalytic cycle (S0-to-S4 oxidation states). Light-harvesting proteins in the complex capture solar photons that energize the manganese-calcium cluster and drive a series of oxidations and proton transfers that in the final S4 state forms the bond between oxygen atoms that yields molecular oxygen.
Scientific teams in the past, including several led by Yachandra and Yano, have shed much light on the S0 through S3 oxidation states of the manganese-calcium cluster, which remain stable for several seconds. However, the S4 state is highly reactive and has not yet been fully characterized in experiments.

"Capturing the S4 state in a time-resolved manner will be essential for understanding the water-oxidation mechanism,"  Yano says. "While X-ray diffraction is clearly the technique of choice for such detailed structural studies, the inherent radiation sensitivity of the manganese-calcium cluster poses a major challenge for protein crystallography on synchrotron radiation sources."

SLAC's LCLS is an X-ray laser powered by a two-mile-long linear accelerator (or linac) that generates pulses of X-ray light on a femtosecond timescale. These pulses are more than a billion times brighter than those from the most powerful synchrotrons. Yachandra, Yano and their colleagues suspended photosystem II microcrystals in a liquid that was jet-streamed into the path of the pulsed light. The diffraction of LCLS X-rays passing through the photosystem II microcrystals created patterns that computers reconstructed into images of the complex's composition and atomic structure at a resolution of 6.5 angstroms - one ten-billionth of a meter or about the diameter of a hydrogen atom.

"We hope that with improved samples, in the future we will be able to get to a higher resolution - perhaps 3 angstroms or better," says Jan Kern, a research scientist at Berkeley Lab and SLAC who was the lead author on the PNAS paper.

Photosystem II microcrystals (approximately 10 micrometers in diameter)were used as a matter of efficiency. Molecular reconstruction through X-ray diffraction requires the examination of literally millions of crystals, since each shot from the LCLS destroys the specimen.

"Because it takes months to grow sufficient quantities of the photosystem II complex in bacterial culture, the use of microcrystals made the most efficient use of time and materials," says Kern. "Also, microcrystals were much easier to direct toward the LCLS X-ray beam using the liquid-stream sample delivery system developed by our collaborators at SLAC."

Paul Adams and Nicholas Sauter, also with Berkeley Lab's Physical Biosciences Division and also co-authors of the PNAS paper, led the data analysis in this study, writing new software to manage the computations.

"Doing this study was a monumental achievement that required a large team to make it happen," Sauter says. "We injected crystal samples into the beam at a rate of 120 per second, and after a week we had 63 Terabytes of data from which we selected the best 7,000 diffraction images to reconstruct photosystem II's molecular structure."

Further studies at the LCLS by the research team are already underway using both X-ray diffraction and spectroscopy techniques to investigate the intermediate reaction states formed in the photosystem II complex as it undergoes photooxidation.

"We hope to learn from nature's design principles and apply that knowledge to the design and development of artificial photosynthetic systems," Yano says.

Further Information
Access to this exclusive content is for Technology Networks Premium members only.

Join Technology Networks Premium for free access to:

  • Exclusive articles
  • Presentations from international conferences
  • Over 2,600+ scientific posters on ePosters
  • More than 3,800+ scientific videos on LabTube
  • 35 community eNewsletters

Sign In

Forgotten your details? Click Here
If you are not a member you can join here

*Please note: By logging into you agree to accept the use of cookies. To find out more about the cookies we use and how to delete them, see our privacy policy.

Related Content

Industry-Sponsored Academic Inventions Spur Increased Innovation
Analysis questions assumption that corporate support skews science toward inventions that are less useful than those funded by the government or non-profit organizations.
Monday, March 24, 2014
Scientific News
Pittcon Announces Sanford Asher as Recipient of the 2016 SACP Award
Asher will accept this prestigious award at Pittcon 2016 in Atlanta, Georgia.
Metamaterial Absorbers for Infrared Inspection Technologies
A metamaterial absorber capable of highly sensitive infrared detection enhances the spectroscopy of tiny molecular details.
Pancreatic Cancer Stem Cells Could be "Suffocated" by Anti-diabetic Drug
A new study shows that pancreatic cancer stem cells (PancSCs) are virtually addicted to oxygen-based metabolism, and could be “suffocated” with a drug already used to treat diabetes.
Marzipan Made From Pure Almonds
Researchers carry out DNA analyses and use advanced protein identification techniques to determine whether marzipan is made from pure almonds or also contains other nuts or beans.
Evidence of Ancient Life Discovered Deep Below the Seafloor
Ancient rocks harbored microbial life deep below the seafloor, reports a team of scientists from the Woods Hole Oceanographic Institution (WHOI), Virginia Tech, and the University of Bremen.
Kwansei Gakuin University in Hyogo, Japan, Uses Raman Microscopy
Raman Microscopy study crystallographic defects in silicon carbide wafers.
Structural Discoveries Could Aid in Better Drug Design
Scientists have uncovered the structural details of how some proteins interact to turn two different signals into a single integrated output.
X-ray Laser Experiment Could Help in Designing Drugs for Brain Disorders
Scientists found that when two protein structures in the brain join up, they act as an amplifier for a slight increase in calcium concentration, triggering a gunshot-like release of neurotransmitters from one neuron to another.
Team Identifies Structure of Tumor-Suppressing Protein
An international group of researchers led by Carnegie Mellon University physicists Mathias Lösche and Frank Heinrich have established the structure of an important tumor suppressing protein, PTEN.
Major Innovation in Molecular Imaging Delivers Spatial and Spectral Info Simultaneously
Berkeley Lab scientist invents technique to combine spectroscopy with super-resolution microscopy, enabling new ways to examine cell structures and study diseases.

Skyscraper Banner
Go to LabTube
Go to eposters
Access to the latest scientific news
Exclusive articles
Upload and share your posters on ePosters
Latest presentations and webinars
View a library of 1,800+ scientific and medical posters
2,600+ scientific and medical posters
A library of 2,500+ scientific videos on LabTube
3,800+ scientific videos