First Snapshots Of Water Splitting In Photosynthesis

First Snapshots Of Water Splitting In Photosynthesis

140709140117-large (1)
An international team, led by Arizona State University scientists, has published today in Nature a groundbreaking study that shows the first snapshots of photosynthesis in action as it splits water into protons, electrons and oxygen – the process that maintains Earth’s oxygen atmosphere.

“This study is the first step towards our ultimate goal of unraveling the secrets of water splitting and obtaining molecular movies of biomolecules,” said Petra Fromme, professor of chemistry and biochemistry at ASU. Fromme is the senior author and leader of the international team, which reported their work in “Serial time-resolved crystallography of photosystem II using a femtosecond X-ray laser,” in the July 9 online issue of Nature.

Photosynthesis is one of the fundamental processes of life on Earth. The early Earth contained no oxygen and was converted to the oxygen-rich atmosphere we have today 2.5 billion years ago by the “invention” of the water splitting process in Photosystem II (PSII). All higher life on Earth depends on this process for its energy needs, and PSII produces the oxygen we breathe, which ultimately keeps us alive.

The revealing of the mechanism of this water splitting process is essential for the development of artificial systems that mimic and surpass the efficiency of natural systems. The development of an “artificial leaf” is one of the major goals of the ASU Center for Bio-Inspired Solar Fuel Production, which was the main supporter of this study.

“A crucial problem facing our Center for Bio-Inspired Fuel Production (Bisfuel) at ASU and similar research groups around the world is discovering an efficient, inexpensive catalyst for oxidizing water to oxygen gas, hydrogen ions and electrons,” said ASU Regents’ Professor Devens Gust, the center’s director. “Photosynthetic organisms already know how to do this, and we need to know the details of how photosynthesis carries out the process using abundant manganese and calcium.

“The research by Fromme and coworkers gives us, for the very first time, a look at how the catalyst changes its structure while it is working,” Gust added. “Once the mechanism of photosynthetic water oxidation is understood, chemists can begin to design artificial photosynthetic catalysts that will allow them to produce useful fuels using sunlight.”

In photosynthesis, oxygen is produced at a special metal site containing four manganese atoms and one calcium atom, connected together as a metal cluster. This oxygen-evolving cluster is bound to the protein PSII that catalyzes the light-driven process of water splitting. It requires four light flashes to extract one molecule of oxygen from two water molecules bound to the metal cluster.

Fromme states that there are two major drawbacks to obtaining structural and dynamical information on this process by traditional X-ray crystallography. First, the pictures one can obtain with standard structural determination methods are static. Second, the quality of the structural information is adversely affected by X ray damage.

“The trick is to use the world’s most powerful X-ray laser, named LCLS, located at the Department of Energy’s SLAC National Accelerator Laboratory,” said Fromme. “Extremely fast femtosecond (10 -15 second) laser pulses record snapshots of the PSII crystals before they explode in the X-ray beam, a principle called ‘diffraction before destruction.’”

In this way, snapshots of the process of water splitting are obtained damage-free. The ultimate goal of the work is to record molecular movies of water splitting.

The team performed the time-resolved femtosecond crystallography experiments on Photosystem II nanocrystals, which are so small that you can hardly see them, even under a microscope. The crystals are hit with two green laser flashes before the structural changes are elucidated by the femtosecond X-ray pulses.

The researchers discovered large structural changes of the protein and the metal cluster that catalyzes the reaction. The cluster significantly elongates, thereby making room for a water molecule to move in.

“This is a major step toward the goal of making a movie of the molecular machine responsible for photosynthesis, the process by which plants make the oxygen we breathe, from sunlight and water,” explained John Spence, ASU Regents’ Professor of physics, team member and scientific leader of the National Science Foundation-funded BioXFEL Science and Technology Center, which develops methods for biology with free electron lasers.

ASU recently made a large commitment to the groundbreaking work of the femtosecond crystallography team by planning to establish a new Center for Applied Structural Discovery at the Biodesign Institute at ASU. The center will be led by Petra Fromme.

Student role in research

An interdisciplinary team of eight ASU faculty members from the Department of Chemistry and Biochemistry (Petra Fromme, Alexandra Ros, Tom Moore and Anna Moore) and the Department of Physics (John Spence, Uwe Weierstall, Kevin Schmidt and Bruce Doak) worked together with national and international collaborators on this project. The results were made possible by the excellent work of current ASU graduate students Christopher Kupitz, Shibom Basu, Daniel James, Dingjie Wang, Chelsie Conrad, Shatabdi Roy Chowdhury and Jay-How Yang, as well as ASU doctoral graduates and post-docs Kimberley Rendek, Mark Hunter, Jesse Bergkamp, Tzu-Chiao Chao and Richard Kirian.

Two undergraduate students, Danielle Cobb and Brenda Reeder, supported the team and gained extensive research experience by working hand-in-hand with graduate students, researchers and faculty at the free electron laser at Stanford. Four ASU senior scientists and postdoctoral researchers (Ingo Grotjohann, Nadia Zatsepin, Haiguang Liu and Raimund Fromme) supported the faculty in the design, planning and execution of the experiments, and were also instrumental in evaluation of the data.

The first authorship of the paper is jointly held by ASU graduate students Christopher Kupitz and Shibom Basu. Kupitz’s dissertation is based on the development of new techniques for the growth and biophysical characterization of nanocrystals, and Basu devoted three years of his doctoral work to the development of the data evaluation methods.

“It is so exciting to be a part of this groundbreaking research and to have the opportunity to participate in this incredible international collaboration,” said Kupitz, who will graduate this summer with a doctorate in biochemistry. “I joined the project because it fascinates me to work at the LCLS accelerator on this important biological project.”

“The most exciting aspect of the work on Photosystem II is the prospect of making molecular movies to witness the water splitting process through time-resolved crystallography,” added Basu.

National and international collaborators on the project include the team of Henry Chapman at DESY in Hamburg, Germany, who, with the ASU team and researchers at the MPI in Heidelberg, pioneered the new method of serial femtosecond crystallography. Other collaborators included a team led by Matthias Frank, an expert on laser spectroscopy and time-resolved studies with FELs at Lawrence Livermore National Laboratory, and the team of Yulia Pushkar at Purdue University, who supported the work with characterization of the crystals by electron paramagnetic resonance.

“We’re tantalizingly close,” said Chapman of the Center for Free-Electron Laser Science at DESY and a pioneer in X-ray-free laser studies of crystallized proteins. “I think this shows that we really are on the right track and it will work.”

Additional collaborators include scientists from SLAC, Lawrence Berkeley National Laboratory; the Stanford PULSE Institute; Max Planck Institutes for medical research and nuclear physics; the University of Hamburg; the European X-ray Free-Electron Laser and the Center for Ultrafast Imaging; the University of Melbourne in Australia; Uppsala University in Sweden; and University of Regina in Canada.

The work was supported by the Department of Energy’s Office of Science, the National Institutes of Health, the National Science Foundation, German Research Foundation (DFG), the Max Planck Society, the SLAC and Lawrence Livermore National Laboratory Directed Research and Development programs, and the BioXFEL Science and Technology Center, among others.

Story Source:

The above story is based on materials provided by Arizona State UniversityNote: Materials may be edited for content and length.

The Most Amazing Thing About Trees

The Most Amazing Thing About Trees

Trees create immense negative pressures of 10’s of atmospheres by evaporating water from nanoscale pores, sucking water up 100m in a state where it should be boiling but can’t because the perfect xylem tubes contain no air bubbles, just so that most of it can evaporate in the process of absorbing a couple molecules of carbon dioxide. Now I didn’t mention the cohesion of water (that it sticks to itself well) but this is implicit in the description of negative pressure, strong surface tension etc.

[msa-ads data-ad-client=”ca-pub-6965588547261395″ data-ad-slot=”7732882042″]

Earth; The Pale Blue Dot

Earth; The Pale Blue Dot

Killer asteroid confirmed to be responsible for dinosaur extinction:

Scientists have unearth credible evidence to confirm a large asteroid was responsible for the extinction of the dinosaurs over 66 million years ago, it has been announced. This particular extinction event, which paved the way for the evolution of our species, has been attributed to several different things over the years. Fromclimate change, a nuclear winter caused by basaltic lava eruptions of massive volcanoes in western India, an influx of radiation from a nearby supernova explosion (or perhaps a gamma-ray burst) to finally, an asteroid impact., which has been a favorite of biologist and paleontologist over the course of the past few decades.

According to Paul Renne, the director at Berkeley University’s Geochronology Center in California, the asteroid impact was quite likely one of several contributing factors to the downfall of the prehistoric animals, as many of them were already on their way to extinction; however, Renne claims that this was the main catalyst that “pushed Earth past the tipping point.”

The collision was never in question, but the exact date of it is. Scientists have been trying to determine if the impact took place more than 300,000 years after the last of the dinosaurs had already died off in the Cretaceous-Tertiary extinction event, which is where Renne and his team comes in: Using high-precision radiometric dating analysis, in this case “argon-argon dating,” the team were able to determine the most precise date yet of the impact: 66,038,000 years ago – give or take 11,000, which coincides with the impact of an asteroid or a comet in the Caribbean off the Yucatan coast of Mexico. “We have shown that these events are synchronous to within a gnat’s eyebrow,” Renne continued.

Argon-argon dating is perhaps, one of the most reliable means of determine how long a sample of materials have been decaying, as it utilizes the fact that potassium, a naturally radioactive element, decays into argon with regularity.

The Destruction of Asteroid Impacts:

[msa-ads data-ad-client=”ca-pub-6965588547261395″ data-ad-slot=”7732882042″]

It only takes a relatively small asteroid to cause quite a bit of destruction on our planet, as any object large enough to survive the descent through Earth’s atmosphere would acquire quite a bit of kinetic energy before it hits the surface of the planet, travelling at VERY fast speeds. Just to throw out one example of this, if an object had a diameter of about 10 kilometers and was travelling at speeds between [approximately] 15 to 20 kilometers per second, it would have a kinetic energy equal to 300 million nuclear bombs, going off simultaneously.

Almost instantly after the impact, the Earth would undergo rapid changes, including; “intense blinding light, severe radiation burns, a crushing blast wave, lethal balls of hot glass, winds with speeds of hundreds of kilometres per hour, and flash fires.” The rubble would be forced into the stratosphere, where it would block a majority of the sunlight from the plants and animals on the ground, which becomes problematic for the photosynthesis plants must undergo to derive energy to survive. With no plants converting sunlight into energy, our oxygen levels would decrease dramatically. I don’t have to explain why that is not an ideal situation to find ourselves in.

The asteroid that hit our planet at the end of the Mesozoic Era was almost 6 miles (10 km) across, generating more energy than nearly 100 trillion tons of TNT, which is more than a billion times more energetic than the bombs that destroyed Nagasaki and Hiroshima during WWII — ultimately leaving behind a crater named Chicxulub, which is more than 110 miles (180 kilometers) wide.

By Jaime Trosper

For Further Reading:

The paper has been published in the journal of science, here you can see it in its entirety;

“Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary:”
http://www.sciencemag.org/content/339/6120/684

“Dinosaur extinction: Scientists estimate ‘most accurate’ date:”
http://www.bbc.co.uk/news/uk-scotland-glasgow-west-21379024

” Dinosaur Extinction & Chicxulub Asteroid Impact Most Likely Coincided, Study Says:”
http://www.huffingtonpost.com/2013/02/08/dinosaur-extinction-chixulub-asteroid-impact_n_2639911.html

Image Credit: SMBC Comics

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 Unported License.