From Sunlight to Oxygen: Researchers Capture Hidden Stage in Photosynthesis
Photosynthesis, the fundamental force behind life on our planet, continues to hold numerous enigmatic facets. One such enigma lies in the intricate workings of Photosystem II, a protein complex found in plants, algae, and cyanobacteria. How does this remarkable system harness sunlight’s energy to split water, ultimately producing the life-sustaining oxygen we breathe?
Finally, a breakthrough has emerged as researchers from the esteemed Lawrence Berkeley National Laboratory and SLAC National Accelerator Laboratory, in collaboration with experts from Uppsala University, Humboldt University, and other prestigious institutions, decipher a key secret of Photosystem II. Their relentless pursuit of knowledge has paid off.
Photosynthesis, a fundamental process shaping Earth’s ecosystem, remains shrouded in mystery despite its pivotal role. Specifically, the mechanism by which Photosystem II, a protein complex found in plants, algae, and cyanobacteria, harnesses solar energy to split water and generate breathable oxygen has long eluded scientific comprehension.
Scientists have made a groundbreaking discovery in their efforts to understand photosynthesis. By utilizing the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory, and the SPring-8 Angstrom Compact free electron Laser (SACLA) in Japan, researchers were able to capture, in unprecedented detail, the moments leading up to the release of breathable oxygen during photosynthesis.
The data uncovered an intermediate reaction step that had not been observed before, and was published in a recent issue of the prestigious scientific journal, Nature. This discovery sheds new light on how nature has perfected the process of photosynthesis, and has the potential to greatly benefit the development of artificial photosynthetic systems.
By mimicking the natural process of photosynthesis, scientists hope to harvest sunlight to create sustainable and clean energy sources by converting carbon dioxide into hydrogen and carbon-based fuels.
“The more we learn about how nature does it, the closer we get to using those same principles in human-made processes, including ideas for artificial photosynthesis as a clean and sustainable energy source,” says co-author Jan Kern.
“Photosystem II is giving us the blueprint for how to optimize our clean energy sources and avoid dead ends and dangerous side products that damage the system,” adds Co-author Junko Yano.
“What we once thought was just fundamental science could become a promising avenue to improving our energy technologies.”
Game-Changing Photosynthesis: Unveiling the Molecular Players
In the intricate dance of photosynthesis, the oxygen-evolving center of Photosystem II takes center stage. This crucial center, composed of four manganese atoms and one calcium atom connected by oxygen atoms, orchestrates a series of intricate chemical reactions, ultimately leading to the separation of water molecules and the release of life-sustaining molecular oxygen.
Similar to a baseball game, the oxygen-evolving center progresses through four distinct oxidation states, aptly named S0 through S3, as it interacts with sunlight. Drawing a parallel to a baseball field, S0 represents the starting point, with a player poised on home base, ready to swing the bat. S1-S3 correspond to players positioned on first, second, and third bases. Each time a batter connects with a ball or the oxygen-evolving center absorbs a photon of sunlight, the player advances one base. When the fourth ball is hit, the player gracefully slides into home, resulting in a run or, in the context of Photosystem II, the liberation of a molecule of breathable oxygen.
To unravel this intricate process, researchers conducted experiments that involved exciting samples from cyanobacteria using optical light, followed by probing them with ultrafast X-ray pulses from the cutting-edge LCLS and SACLA facilities. These groundbreaking experiments unveiled the atomic structure of the cluster and shed light on the underlying chemical processes at play.
Researchers Successfully Visualize the Final Phase of Oxygen Production in Photosynthesis
In a remarkable feat, researchers successfully visualized the decisive moment in photosynthesis, likened to a thrilling sprint towards home plate in baseball. This critical stage, known as the transient state or S4, involves the bonding of two oxygen atoms to form an oxygen molecule that is subsequently released. Astonishingly, the data unveiled previously unseen intermediate steps in this reaction.
“Other experts argued that this is something that could never be captured,” explains co-author Uwe Bergmann. “It’s really going to change the way we think about Photosystem II. Although we can’t say we have a unique mechanism based on the data yet, we can exclude some models and ideas people have proposed over the last few decades. It’s the closest anyone has ever come to capturing this final step and showing how this process works with actual structural data.”
This groundbreaking study marks the culmination of a decade-long research endeavor by the team. Previous investigations focused on observing various stages of the photosynthetic cycle under natural temperature conditions.
“Most of the process that produces breathable oxygen happens in this last step,” adds co-author Vittal Yachandra. “But there are several things happening at different parts of photosystem II and they all have to come together in the end for the reaction to succeed. Just like how in baseball, factors like the location of the ball and the position of the basemen and fielders affect the moves a player takes to get to home base, the protein environment around the catalytic center influences how this reaction plays out.”
Advancing X-ray Technology for a Promising Future
Building upon these findings, the research team has outlined plans to undertake additional experiments aimed at capturing numerous snapshots of the photosynthesis process.
“There are still things happening in between that we could not catch yet,” Kern adds. “There are more snapshots we really want to take which would bridge the remaining gaps and tell the whole story.”
To accomplish this, further enhancement of data quality is required. Previously, this posed a challenge due to the faint X-ray signals emitted by the samples and the limited pulse rates of existing X-ray lasers like LCLS and SACLA.
“It took quite some effort to optimize the setup, so we couldn’t collect all the data we needed for this one publication in a single experiment,” adds co-author and SLAC scientist Roberto Alonso-Mori. “These results actually include data taken over six years.”
However, the imminent launch of LCLS-II, an upgraded version of LCLS, promises a dramatic increase in repetition rate from 120 pulses per second to potentially one million per second.
“With these upgrades, we will be able to collect several days’ worth of data in just a few hours,” Bergmann adds. “We will also be able to use soft X-rays to further understand the chemical changes happening in the system. These new capabilities will continue to drive this research forward and shed new light on photosynthesis.”
Source: 10.1038/s41586-023-06038-z
Image Credit: Getty