Researchers from Michigan State University and colleagues from the University of California at Berkeley, the University of South Bohemia and the Lawrence Berkeley National Laboratory have helped reveal the most detailed picture to date of important biological “antennae”.
Nature 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 capable of absorbing sunlight, water and carbon dioxide and turning them into sugars and oxygen.
Published on August 31 in the magazine Nature, the results immediately shed new light on microbial photosynthesis, particularly how light energy is captured and sent where it is needed to fuel the conversion of carbon dioxide into sugars. Moving forward, the insights could also help researchers remedy harmful bacteria in the environment, develop artificial photosynthetic systems for renewable energy, and enlist microbes in sustainable production that begins with 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 design like the one we’ve provided in this study, you can start thinking about fine-tuning and optimizing the light-gathering component of photosynthesis.”
“Once you see how something works, you have a better idea of how to modify and manipulate it. This is a big plus,” said Markus Sutter, a senior research associate at Kerfeld Lab, who works at MSU and Berkeley Lab in California.
Cyanobacterial antenna structures, which are called phycobilisomes, are complex collections of pigments and proteins, which assemble into relatively massive complexes.
For decades, researchers have worked to visualize the different building blocks of phycobilisomes to try to understand how they are put together. Phycobilisomes are fragile and require this piecemeal approach. Historically, researchers have not been able to obtain the high-resolution images of intact antennas needed to understand how they capture and conduct light energy.
Now, thanks to an international team of experts and advances in a technique known as cryo-electron microscopy, the structure of a cyanobacterial light-gathering antenna is available in near-atomic resolution. The team included researchers from MSU, Berkeley Lab, University of California, Berkeley, and University of South Bohemia in the Czech Republic.
“We have been fortunate to be a team of people with complementary skills, people who have worked well together,” said Kerfeld, who is also a member of the MSU-DOE Plant Research Laboratory, supported by the US Department of Energy. . “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 light-gathering structure of a cyanobacteria antenna was missing,” Sauer said. “Our discovery helps us understand how evolution found a way to turn carbon dioxide and light into oxygen and sugar in bacteria, long before there was any plant on our planet.”
Along with Kerfeld, Sauer is the corresponding author of the new article. The team documented several noteworthy findings, including the search for a new phycobilisome protein and the observation of two new ways in which the phycobilisome orients its light-catching rods that had not been resolved before.
“That’s 12 pages of discoveries,” said María Agustina Domínguez-Martín of the Nature report. As a postdoctoral researcher at the Kerfeld Lab, Domínguez-Martín initiated the study at the MSU and completed it at the Berkeley Lab. He is currently at the University of Cordoba in Spain as part of the scholarship Marie Sk? owdoska-Curie postdoctoral doctor. “It has been a long journey full of beautiful surprises”.
One surprise, for example, has come in how a relatively small protein can act as a surge protector for the huge antenna. Prior to this work, researchers knew that the phycobilisome could enclose molecules called orange carotenoid proteins, or OCPs, when the phycobilisome had absorbed too much sunlight. OCPs release excess energy in the form of heat, protecting a cyanobacterium’s photosynthetic system from burning.
Until now, there has been a debate about how many OCPs the phycobilisome could bind and where those 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 are slow to turn off their photoprotection after it has done its job. Now, with the full picture of how the surge protector works, researchers can design ways to design “smart” and less expensive photoprotection, Kerfeld said.
And while they’ve helped make the planet habitable for humans and countless other organisms that need oxygen to survive, cyanobacteria have a dark side. Cyanobacteria that flourish in lakes, ponds and reservoirs can produce deadly toxins for native ecosystems as well as for humans and their pets. Having a blueprint on how bacteria not only harvest solar energy but also protect themselves from too much of it could inspire new ideas for attacking harmful blooms.
In addition to 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 this as Legos, you can keep building, right? Proteins and pigments are like building blocks that form the phycobilisome, but then it’s part of the photosystem, which is in the cell membrane, which is part of the whole cell. “said Sutter. “We are climbing the ladder of the ladder in a sense. We have found something new on our step, but we cannot say that we have fixed the system.”
“We answered some questions, but we opened the doors to others and, for me, that’s what makes it a breakthrough,” said Domínguez-Martín. “I am thrilled to see how the field develops from here.”
This work was supported by the US Department of Energy 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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