A team of researchers at Rensselaer Polytechnic Institute (RPI), Pennsylvania State University, Yale University, and Louisiana State University has revealed the structure of a modified and evolved version of Photosystem I (PS I), a key protein complex used by plants and cyanobacteria to convert sunlight into chemical energy. This discovery sheds light on the evolution and adaptation of photosynthetic organisms and could potentially lead to new, highly efficient systems for producing renewable solar fuels.

The research was led by K. V. Lakshmi at RPI’s Baruch ’60 Center for Biochemical Solar Energy Research. The center, established by Johanna and Tom Baruch, RPI Class of 1960 and Trustee Emeritus, is focused on understanding and enhancing the rates of photosynthetic processes, such as light harvesting, electron transport, and increasing the yield of products under changing environmental conditions.

Photosynthesis is the process that powers life on Earth by allowing plants and certain bacteria to harness sunlight and produce chemical energy. One crucial part of this process is the photosynthetic protein PS I, which helps turn light into usable chemical energy. By examining the structure and function of PS I in unprecedented detail, scientists can understand the adaptation of photosynthetic processes under changing environmental conditions and learn to harness them for human-made artificial solar energy systems that could produce renewable fuels, such as hydrogen, a clean energy source.

In a new breakthrough study published in the journal Science Advances, the researchers focused on a modified version of PS I isolated from a cyanobacterium (a.k.a., blue-green algae). Although natural PS I contains a molecule called phylloquinone to transfer electrons, evolution and adaptation led to a variant with an alternate molecule called DMPBQ. Swapping the phylloquinone molecule is a major discovery, as it can help scientists understand how organisms can adapt their photosynthetic machinery to varying environmental conditions. This discovery suggests that the electron carrier can be swapped with other molecules that could allow PS I to be connected to catalysts that generate hydrogen, effectively turning the protein into a tiny solar-powered fuel factory.

The study used a cutting-edge technique known as cryogenic electron microscopy to capture a highly detailed picture of the modified PS I. With a resolution of 2.0 Ångströms (less than a millionth of a millimeter), the research provided new insights into how PS I interacts with different quinones — molecules involved in the transfer of electrons, which is essential for converting sunlight into energy.

These new insights will help scientists understand how and why these molecules are swapped as photosynthetic organisms evolve and adapt in nature, and in the future, may inform a design for improved versions of PS I for creating solar fuels. According to Lakshmi, the lead corresponding author of the study, "Increasing global population and climate change uncertainties have compelled enhanced photosynthetic efficiency and yields over the coming decades. This presents a need for a thorough understanding of the adaptation of photosynthetic systems to changes in the environment and the key factors limiting photosynthesis. The knowledge gained in this breakthrough study helps us understand the adaptation of photosynthetic bacteria to environmental stressors and could help develop new, nature-inspired technologies for producing clean energy.” 

 “This discovery led us to reconsider how quickly organisms can evolve, even under controlled laboratory conditions,” added Penn State’s John Golbeck, co-corresponding author.

"Understanding how these proteins work at such a fine level is essential for us to engineer systems with higher efficiency and yields. The discovery is part of a larger effort to create engineered photosynthetic systems that use natural processes to produce renewable fuels," said the University of Wisconsin-Madison’s Chris Gisriel (formerly at Yale University), a primary author of the publication. 

Current methods for producing hydrogen often rely on fossil fuels or inefficient processes, but PS I-based systems have the potential to revolutionize the field by providing a more sustainable and effective solution. This work lays the foundation for further research into bioengineered energy systems and could eventually contribute to the development of large-scale, eco-friendly fuel production, helping to reduce our dependence on fossil fuels and combat climate change.

This research was funded by the Photosynthetic Systems Program in the U.S. Department of Energy’s Office of Basic Energy Sciences and the National Institutes of Health.