Researchers help reveal a ‘blueprint’ for photosynthesis

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

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

Published on August 31 in the magazine Nature, the findings immediately shed new light on microbial photosynthesis — specifically how light energy is captured and directed to where it’s needed to boost the conversion of carbon dioxide into sugars. In the future, the insights could also help researchers remove harmful bacteria from the environment, develop artificial photosynthetic systems for renewable energy and enable microbes for sustainable production that starts with the raw materials of carbon dioxide and sunlight.

“There is a lot of interest in using cyanobacteria as solar-powered factories that capture sunlight and convert it into a type of energy that can be used to make important products,” said Cheryl Kerfeld, Hannah Distinguished Professor of Structural Bioengineering at the College. of Natural Science. “With a blueprint like the one we’ve provided 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 to modify and manipulate it. That’s a big advantage,” said Markus Sutter, senior research associate in the Kerfeld Lab, which operates at MSU and Berkeley Lab in California. .

The cyanobacterial antennae structures, called phycobilisomes, are complex collections of pigments and proteins that come together to form relatively massive complexes.

For decades, researchers have worked to visualize the different building blocks of phycobilisomes to try to understand how they’re put together. Phycobilisomes are vulnerable, making this fragmented approach necessary. Historically, researchers have failed to get the high-resolution images of intact antennas necessary to understand how they capture and conduct light energy.

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 now available with 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 fortunate to be a team made up of people with complementary expertise, people who worked well together,” said Kerfeld, who is also a member of the MSU-DOE Plant Research Laboratory, which is supported by the U.S. Department of Energy. “The group had the right chemistry.”

‘A long journey full of nice surprises’

“This work is a breakthrough in photosynthesis,” said Paul Sauer, a postdoctoral researcher in Professor Eva Nogales’ cryogenic electron microscopy lab at Berkeley Lab and UC Berkeley.

“The entire light-harvesting structure of the cyanobacterial antennae has been missing until now,” Sauer said. “Our discovery helps us understand how evolution devised ways to convert carbon dioxide and light to oxygen and sugar in bacteria long before plants existed on our planet.”

Along with Kerfeld, Sauer is a corresponding author of the new article. The team documented several remarkable results, including finding a new phycobilisome protein and observing two new ways the phycobilisome orients its light-trapping rods that had not been resolved before.

“It’s 12 pages of discoveries,” says María Agustina Domínguez-Martín of the Nature report. As a postdoctoral researcher in the Kerfeld Lab, Domínguez-Martín started the research at MSU and completed it at the Berkeley Lab. She is currently affiliated with the University of Cordoba in Spain as part of the Marie Sk?owdoska-Curie Postdoctoral Fellowship. “It’s been a long journey full of nice surprises.”

One surprise, for example, was how a relatively small protein can act as a surge protector for the huge antenna. Before this work, researchers knew that the phycobilisome could corral molecules called orange carotenoid proteins, or OCPs, when the phycobilisome absorbed too much sunlight. The OCPs release the excess energy as heat and protect the photosynthetic system of a cyanobacterium from combustion.

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

This kind of surge protection system — called photoprotection and has analogs in the plant world — naturally tends to be wasteful. Cyanobacteria are slow to turn off their photoprotection after they’ve done their job. Now, with the complete picture of how surge protection works, researchers can design ways to develop “smart,” less wasteful photo protection, Kerfeld said.

And despite helping make the planet habitable for humans and countless other organisms that need oxygen to survive, cyanobacteria have a dark side. Cyanobacteria blooms in lakes, ponds and reservoirs can produce toxins that are deadly to native ecosystems as well as humans and their pets. Having a blueprint of how the bacteria not only collect the sun’s energy, but also protect themselves from it could inspire new ideas for attacking harmful flowers.

In addition to the new answers and possible 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 this as Lego, you can keep building, right? The proteins and pigments are like blocks that make 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 are in a sense climbing the ladder of scale. We have found something new in our sport, but we cannot say that we have settled the system.”

“We have answered some questions, but we have opened the doors for 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.