Mechanism of photosynthetic water-splitting revealed by an X-ray free electron laser

August 24, 2017, Okayama University
Mechanism of photosynthetic water-splitting revealed by an X-ray free electron laser
Figure 1: Structural changes of the Mn4CaO5-cluster induced by two flashes of illumination. S1-state: without illumination; S3-state: after two flashes of illumination. Credit: Okayama University

Photosystem II (PSII) is a huge membrane-protein complex that catalyzes light-induced water-splitting, leading to the generation of protons and molecular oxygen. This reaction converts light-energy from the sun into chemical energy that is required to sustain almost all living activities on Earth. The water-splitting reaction is catalyzed by a Mn4CaO5-cluster embedded within the protein matrix of PSII, and proceeds through five intermediate states called Si-states. The structures of PSII and the Mn4CaO5-cluster have been resolved with atomic resolution, however, mechanisms governing water-splitting are unclear due to the lack of intermediate structures of the enzyme.

Now, Michihiro Suga, Fusamichi Akita, Jian-Ren Shen at Okayama University, and colleagues at institutes including Kyoto University, RIKEN, have clarified and resolved the structure of the Mn4CaO5-cluster at S3-state—an intermediate state that exists immediately before the formation of molecular , generated by two flashes of optical illumination. They employed a pump-probe method where two laser flashes were used to pump the enzyme to the intermediate state, and the X-ray diffraction data were collected by a serial-femtosecond crystallography method using femtosecond X-ray free electron lasers (XFEL) at SACLA, Japan.

The results showed the insertion of a new oxygen atom (water molecule) close to an already existing oxo-oxygen termed O5, enabling the formation of between O5 and the newly inserted oxygen atom (O6). This clearly demonstrated the mechanism governing the catalyzed by PSII, and provided a blueprint for design and synthesis of efficient artificial catalysts that in the future could be utilized in artificial photosynthesis to produce clean and renewable energy from the sun.

Explore further: Damage-free structure of photosystem II and the synthesis of model compounds for water-oxidation

More information: Michihiro Suga et al. Light-induced structural changes and the site of O=O bond formation in PSII caught by XFEL, Nature (2017). DOI: 10.1038/nature21400

Related Stories

Tofu-like crystalline catalysts for producing clean energy

September 19, 2013

Research by Professor Jian-Ren Shen at Okayama University demystifies the reaction mechanisms of photosynthesis and the findings may lead to the development of methods for producing an unlimited source of clean energy.

Research clarifies light-harvesting process in plants

June 1, 2016

Photosynthesis, one of the most important biochemical and biophysical processes on earth, provides food and energy for nearly all living organisms (including human beings) in the biosphere. Studying the structures and mechanisms ...

Recommended for you

Producing defectless metal crystals of unprecedented size

October 19, 2018

A research group at the Center for Multidimensional Carbon Materials, within the Institute for Basic Science (IBS), has published an article in Science describing a new method to convert inexpensive polycrystalline metal ...

Nanodiamonds as photocatalysts

October 19, 2018

Climate change is in full swing and will continue unabated as long as CO2 emissions continue. One possible solution is to return CO2 to the energy cycle: CO2 could be processed with water into methanol, a fuel that can be ...

Shining light on the separation of rare earth metals

October 18, 2018

Inside smartphones and computer displays are metals known as the rare earths. Mining and purifying these metals involves waste- and energy-intense processes. Better processes are needed. Previous work has shown that specific ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.