Photosynthesis in unprecedented detail


Rebecca Pool

Tuesday, November 13, 2018 - 14:15
Image: High energy X-rays capture all four stable states of the process that produces the oxygen we breathe, as well as fleeting steps in between.
An international team of researchers has captured a more detailed picture than ever before, of the steps in the reaction mechanisms in photosynthesis.
The results provide the most complete and highest-resolution picture to date of Photosystem II, a key protein complex in plants, algae and cyanobacteria responsible for splitting water and producing oxygen.
As Vittal Yachandra from Berkeley Lab highlights: “It’s like a molecular movie... we’re collecting more and more of these snapshots."
"The idea is eventually to have a continuous story of how water is split into oxygen, and how plants do that using sunlight," he adds.
First frames of a movie of the water oxidation reaction in nature: Light-induced changes observed at the Mn cluster of photosystem II as it goes through its catalytic cycle. [Berkeley Lab]
To study the complex reactions, researchers from Berkeley Lab and SLAC National Accelerator Laboratory joined forces with scientists from Humboldt University of Germany, Umeå University and Uppsala University of Sweden, and the Diamond Light Source, UK.
Using serial femtosecond X-ray crystallography and simultaneous X-ray emission spectroscopy with multi-flash visible laser excitation at room temperature, the researchers imaged different stages of the reaction to 2.04 Å resolution.
In this way, they captured all four intermediate states of the process at room temperature and also revealed, for the first time, transitional moments between two of the states, giving them a sequence of six images of the process.
Berkeley Lab researchers (front row, from left) Iris Young, Sheraz Gul, Ruchira Chatterjee, Junko Yano, Vittal Yachandra, (back, from left) Nigel Moriarty, Jan Kern, Aaron Brewster, and Nicholas Sauter have captured the most complete images of photosynthesis in action. [Marilyn Chung/Berkeley Lab]
Previously, the researchers had determined the room-temperature structure of two of the states at a resolution of 2.25 angstroms, observing the position of the heavy metal atoms.
However, with the new, higher resolution results, they can see the position of lighter atoms, such as oxygen, more clearly, as well as draw a more detailed map of the chemical structure of the metal catalytic center in the complex where water is split.
“This reaction made us as we are, as the world. Molecule by molecule, the planet was slowly enriched until, about 540 million years ago, it exploded with life,” highlights Uwe Bergmann from SLAC. “When it comes to questions about where we come from, this is one of the biggest.”
New X-ray methods have captured the first detailed image of the Photosystem II protein complex at room temperature, which allows scientists to closely watch how water is split during photosynthesis at the temperature at which it occurs naturally.
Key instruments used included SLAC’s Linac Coherent Light Source X-ray laser as well as Berkeley Lab’s Advanced Light Source.
Berkeley Lab researchers, Nicholas Sauter and Paul Adams, also developed software and algorithms to analyse data from the X-ray laser.
“Previously the picture was more blurred and it was difficult to see details,” highlights Berkeley Lab Bioscientist, Jan Kern. “Now we have a sharper picture for these six steps. We estimate that if we get another five or 10 snapshots along the last step in the reaction, that will really tell us what is going on in detail.”
“The entire cycle takes nearly two milliseconds to complete,” he adds. “Our dream is to capture 50-microsecond steps throughout the full cycle, each of them with the highest resolution possible, to create this atomic movie of the entire process.”
New snapshots of photosynthesis captured by X-ray laser.
"We hope a better understanding of photosynthesis and the guiding principles we learn from these studies can then be applied to develop artificial photosynthetic systems, which is a way to produce fuels from sunlight, water, and carbon dioxide," concludes Junko Yano, Berkeley Lab.
Research is published in Nature.
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