Photosynthesis occurs right in front of us each day in countless tiny green leaves, yet the intricate details of this remarkable process remain somewhat elusive. A research group has uncovered another aspect of this complexity. They investigated how the D1 protein, essential for photosynthesis, is formed and introduced a new in-vitro method for analysis. Their findings suggest that approximately 140 proteins might be involved in this procedure, some of which had not been identified before.
Creating the protein complexes necessary for photosynthesis and maintaining them under bright light conditions requires a vast array of supporting proteins.
Photosynthesis takes place before our eyes every day in every single little green leaf — yet the details of the complex process have not yet been fully understood. A research group at Ruhr University Bochum, led by Professor Danja Schünemann, has uncovered another element of this complexity. The team, led by former PhD student Dominique Stolle and current PhD student Lena Osterhoff, examined how the D1 protein, crucial for photosynthesis, is synthesized and developed a new in-vitro technique for this study. It was revealed that there are about 140 proteins likely involved in this process, including some that were previously uncharted. The researchers provided a detailed characterization of one essential protein and shared their findings in the EMBO Journal on August 27, 2024.
Ongoing Repair Process
This study focused on how protein complexes in chloroplasts are formed, paying special attention to D1 protein, a critical element of photosystem II. This protein is embedded in the thylakoid membrane and frequently suffers damage—especially under intense light—necessitating its ongoing degradation and synthesis in a continuous cycle. “The process of breaking down and reconstructing this protein is incredibly intricate, akin to the initial synthesis of the entire photosystem,” says Danja Schünemann. “All the more than 20 subunits of this system must be synthesized within the cell, moved to their specific locations, and then assembled together.”
Observing Ribosomes in Action
To better understand these intricate processes, the research team created a novel in-vitro technique allowing them to purify the ribosomes that are presently synthesizing the D1 protein while they are actively working. “Previously, we could only purify ribosomes on a general level,” explains Danja Schünemann. “Now we can observe their activity firsthand.” The researchers also identified additional elements—beyond the ribosomes—that play a role in assembling the D1 protein. They discovered 140 proteins, some familiar from other biological processes and others that were previously unknown.
For a detailed examination, the team singled out a significant protein: STIC2. “We recognized its crucial role in forming the thylakoid membrane, but the specifics of its function were not clear to us,” the researchers noted. They showed that this protein closely collaborates with another protein, SRP54, during the assembly and repair of the D1 protein. “STIC2 interacts with specific structures in the thylakoid membranes, which is vital for the proper integration of D1 and potentially other key proteins within the photosystems,” adds Danja Schünemann.
Collaborative Efforts
Danja Schünemann’s team worked in collaboration with scholars from the Faculties of Biology and Biotechnology and Chemistry and Biochemistry at Ruhr University Bochum, as well as with teams from the Max Planck Institute of Molecular Plant Physiology in Potsdam.
