Researchers help reveal 'blueprint' for photosynthesis

Researchers help reveal ‘blueprint’ for photosynthesis

#Researchers #reveal #blueprint #photosynthesis

Researchers at Michigan State University and colleagues at the University of California, Berkeley, the University of South Bohemia, and Lawrence Berkeley National Laboratory helped reveal the most detailed but important picture of biological “antennas.”

Nature has developed these structures to harness the sun’s energy through photosynthesis, but these sunlight receptors do not belong to plants. They are found in microbes known as cyanobacteria, the evolutionary descendants of the first organisms on Earth capable of taking sunlight, water and carbon dioxide and converting them into sugars and oxygen.

Published on August 31 in the magazine Nature, The results immediately shed new light on microbial photosynthesis, specifically how light energy is captured and sent where it’s needed to drive the conversion of carbon dioxide into sugars. In the future, the knowledge could also help researchers eliminate harmful bacteria in the environment, develop artificial photosynthetic systems for renewable energy, and engage microbes in sustainable manufacturing that begins with the raw materials carbon dioxide. and sunlight.

“There’s a lot of interest in using cyanobacteria as solar power factories that capture sunlight and convert it into some kind of energy that can be used to make important products,” said Cheryl Kerfeld, Hannah Distinguished Professor of Structural Bioengineering in the College. of Natural Sciences. Sciences. “With a blueprint like the one we provide in this study, you can start thinking about tuning and optimizing the light-harvesting component of photosynthesis. »

“Once you see how something works, you have a better idea of ​​how you can modify and manipulate it. That’s a huge advantage,” said Markus Sutter, a senior research associate at the Kerfeld Lab, which operates out of MSU and Berkeley Lab in California.

The antennae structures of cyanobacteria, called phycobilisomes, are complex assemblies of pigments and proteins, which are assembled into relatively massive complexes.

For decades, researchers have been working to visualize the different building blocks of phycobilisomes to try to understand how they are assembled. Phycobilisomes are fragile and require this stepwise approach. Researchers have historically been unable to obtain the high-resolution images of intact antennas needed to understand how they capture and conduct light energy.

Today, thanks to an international team of experts and advances in a technique known as cryo-electron microscopy, the structure of a cyanobacterial light-harvesting antenna is available at near-atomic resolution. The team included researchers from MSU, Berkeley Lab, the University of California, Berkeley, and the University of South Bohemia in the Czech Republic.

“We were lucky to be a team of people with complementary skills, people who worked well together,” said Kerfeld, who is also a member of the MSU-DOE Plant Research Laboratory, which is supported by the US Department of Energy. USA “The group had the right chemistry. »

“A long journey full of beautiful surprises”

“This work is a breakthrough in the field of photosynthesis,” said Paul Sauer, a postdoctoral researcher in Professor Eva Nogales’ Cryogenic Electron Microscopy Laboratory at Berkeley Lab and UC Berkeley.

“Until now, the complete structure of a cyanobacterial light-harvesting antenna was missing,” Sauer said. “Our discovery helps us understand how evolution found ways to convert carbon dioxide and light into oxygen and sugar in bacteria long before plants existed on our planet. »

Along with Kerfeld, Sauer is a corresponding author on the new paper. The team documented several notable findings, including the discovery of a new phycobilisome protein and the observation of two new ways in which the phycobilisome orients its light-capturing rods that had not previously been resolved.

“There are 12 pages of discoveries,” said María Agustina Domínguez-Martín of the Nature report. As a postdoctoral researcher at the Kerfeld Lab, Domínguez-Martín began the study at MSU and completed it at Berkeley Lab. She is currently at the University of Córdoba in Spain as part of the Marie Skówdoska-Curie Postdoctoral Fellowship. “It was a long journey full of beautiful surprises. »

One surprise, for example, came from how a relatively small protein can act as a spike suppressor for the massive antenna. Before this work, the researchers knew that the phycobilisome could contain molecules called orange carotenoid proteins, or OCPs, when the phycobilisome had absorbed too much sunlight. OCPs release excess energy as heat, protecting the photosynthetic system of a cyanobacterium from combustion.

Until now, there had been debate about how many OCPs the phycobilisome could bind and where these binding sites were. The new research answers these fundamental questions and offers potentially practical insights.

This type of surge protection system, which is called photoprotection and has analogues in the plant world, naturally tends to be wasteful. Cyanobacteria take time to deactivate their photoprotection after doing their job. Now, with a complete picture of how the surge protector works, researchers can design ways to design less expensive, “smart” photoprotection, Kerfeld said.

And while they help make the planet habitable for humans and countless other organisms that need oxygen to survive, cyanobacteria have a dark side. Cyanobacterial blooms in lakes, ponds, and reservoirs can produce toxins that are deadly to native ecosystems as well as humans and their pets. Having a map of how bacteria not only harvest energy from the sun, but also protect themselves from too much energy could inspire new ideas for tackling harmful blooms.

Beyond the new answers and potential applications this work offers, the researchers are also excited about the new questions it raises and the research it could inspire.

“If you think of it like Legos, you can keep piling it up, right? Proteins and pigments are like building blocks that make up the phycobilisome, but that’s part of the photosystem, which is in the cell membrane, which is part of the whole cell. Sutter said. “We climbed the ladder somehow. We found something new on our echelon, but we can’t say we fixed the system. »

“We answered some questions, but we opened the doors to others and, for me, that is what makes it a breakthrough,” Domínguez-Martín said. “I’m excited to see how the field develops from here. »

This work was supported by the US Department of Energy Office of Science, the National Institutes of Health, the Czech Science Foundation, and the European Union’s Horizon 2020 research and innovation program.

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