Plants rely on a process called carbon fixation, which turns carbon dioxide from the air into carbon-rich biomolecules. That is the center of the entire system that cycles carbon through plants, animals, and the atmosphere to sustain life on Earth.
The soilbacteria are the carbon fixing champ. The key step in carbon fixation is carried out by somebacteria 20 times faster than plantbacteria, and figuring out how they do this could help scientists develop forms of artificial photosynthesis to convert the greenhouse gas into fuels, fertilizers, antibiotics and other products.
A group of researchers from the Department of Energy, as well as the University of Concepcin and the Max Planck Institute for Terrestrial Microbiology in Germany, are working together.
Rather than grabbing carbon dioxide molecule and attaching them to biomolecules one at a time, they found, this enzyme consists of pairs of molecules that work in sync, like the hands of a juggler who simultaneously tosses and catches balls, to get the job done faster. One member of each pair opens wide to catch a set of reaction ingredients while the other closes over its captured ingredients and carries out the carbon-fixing reaction.
The team discovered that a single spot of glue held each pair of hands together so they could alternate opening and closing in a coordinated way. The carbon-fixing reaction goes 100 times faster if glue and twist are present.
The most efficient carbon fixer that we know of, and we came up with a neat explanation of what it can do, was the work of Soichi Wakatsuki, a professor at SLAC and one of the senior leaders of the study.
He said that some of the enzymes in the family act slowly, but in a specific way to produce just one product. Now that we know the mechanism, we can engineer enzymes that combine the best features of both approaches and do a very fast job with all sorts of starting materials.
Improving on nature.
The team studied a family of enoyl- CoA carboxylases/reductases. It comes from soilbacteria called Kitasatos setporaae, which can also produce antibiotics.
Six years ago, Wakatsuki heard about this family from two people. The research team had been working to develop bioreactors for artificial photosynthesis to convert carbon dioxide from the atmosphere into all sorts of products.
As important as photosynthesis is to life on Earth, it isn't very efficient. It is only as good as it needs to be, the result of slowly building on previous developments but never inventing something completely new.
He said that the step in natural photosynthesis that fixes CO 2 from the air, which relies on an enzyme called Rubisco, is a roadblock that slows down the whole chain of reactions. It could bring a big boost to efficiency if the ECR enzymes are engineered to go even faster.
We want to design a process that is more efficient by using engineering to rebuild the concepts of nature. This photosynthesis 2.0 could take place in living or synthetic systems, where droplets of water are suspended in oil.
There are portraits of an enzyme.
The nitrogen fixation system converts nitrogen gas from the atmosphere into compounds that living things need. He wasIntrigued by the question of why ECR enzymes were so fast.
Hasan DeMirci, a research associate in Wakatsuki's group who is now an assistant professor at Koc University and investigator with the Stanford PULSE Institute, led the effort at SLAC with help from half a dozen summer interns he supervised.
The samples of the ECR were made by the team at the SLAC and then put into a container to be analyzed with X-rays. The X-rays revealed the structure of the enzyme, which was found on its own and attached to a small molecule that facilitates its work.
The X-ray studies showed how the structure of the enzyme shifted when it was attached to a substrate, a kind ofmolecular workbench that assembles ingredients for the carbon fixing reaction and spurs the reaction along.
A team of researchers from the Linac Coherent Light Source (LCLS) carried out more detailed studies of the enzyme at the SACLA X-ray free-electron laser in Japan. The choice of an X-ray laser allowed them to study the behavior of the enzyme at room temperature with almost no radiation damage.
Detailed biochemical studies and extensive dynamic simulations were carried out by the group in Germany and the group in the University of Concepción in Chile.
The simulations showed that the opening and closing of the two parts of the enzyme involve twisting motions around the central axis of each pair.
He said that the twist is almost like a rachet that can push a finished product out or pull a new set of ingredients into the pocket where the reaction takes place. They can fix carbon 100 times a second with the help of the twisting and synchronization of the enzyme pairs.
A branch of the ECR family can interact with many different kinds of biomolecules to produce a variety of products. Since they aren't held together by glue, they can't coordinate their movements and therefore take a long time.
If we can increase the rate of those sophisticated reactions to make new biomolecules, that would be a significant jump in the field.
There are static shots and fluid movies.
The experiments have produced static snapshots of the reaction ingredients and the final products.
We would combine all the ingredients as they flow into the path of the X-ray laser beam so that we could watch the reaction take place in real time.
He said that the team tried that at SACLA, but it didn't work. We were able to break the crystals when we pressed hard.
He said that an upcoming high-energy upgrade to LCLS will likely solve that problem, as the pulse that arrives a million times per second will be individually adjusted to the ideal strength for each sample.
The team is working with the LCLS sample delivery group and with researchers at the SLAC-Stanford Cryo-EM facilities to find a way to make this approach work.
Major funding from the DOE Office of Science was received by researchers from the RIKEN Spring-8 Center. The work done by the summer interns and the interns made a difference in the study. The ECR samples were produced using the DNA provided by the Joint Genome Institute. The Joint Genome Institute is one of the DOE Office of Science user facilities.
Hasan DeMirci et al. are from the Central Science of the American Chemical Society.
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