Tracing the evolution of photoprotection by ancestral reconstruction: Development of photoswitching and energy dissipation by the Orange Carotenoid Protein

• Applicant: Dr. Marcus Moldenhauer
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560711813

Cyanobacteria represent a remarkable phylum of bacteria that have adapted various mechanisms to harness sunlight through photosynthesis while managing potential damage from high light conditions. A key component of their photoprotective mechanism is the production of the orange carotenoid protein (OCP). This protein undergoes a dynamic transition between an inactive orange state (OCPO) and an active red state (OCPR) in response to strong radiation, regulating energy flow by binding to the light-harvesting antennae, the phycobilisomes, and dissipating excess energy as heat. This process, known as non-photochemical quenching (NPQ), is crucial for balancing light capture and preventing the formation of reactive oxygen species (ROS) that result from excess energy. While recent research has provided significant insights into the OCP photocycle, gaps remain in understanding the contribution of specific amino acids to its function. The proposed research aims to address these gaps by utilizing insights from ancient OCP precursors to investigate the functional roles of specific amino acids. Notably, OCP ancestors have already been constructed in a past study, providing valuable knowledge as foundation for the proposed research. The proposed strategy involves creating chimeric proteins, such as an OCP variant combining extant and ancient features, and characterizing them through time-resolved absorption spectroscopy to examine the role of specific OCP segments in the photocycle. The advantage of this approach lies in the close relation to the already studied ancestral proteins, which differ significantly in their relaxation time constants despite having low sequence variations. This strategy will facilitate the identification of specific amino acids responsible for distinct switching behaviors and provide a deeper understanding of OCP's regulatory mechanisms. Another particularly important but unresolved question is the concrete binding interface of OCP and phycobilisomes for fluorescence quenching, a function that is absent in the oldest ancestor. Understanding why this ancestral protein lack this ability could provide crucial insights into the evolutionary mechanisms underlying efficient energy dissipation. The proposed research aims to uncover these evolutionary adaptations, advancing our knowledge of OCP's regulatory mechanisms to understand the photoprotection in cyanobacteria.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Georg Hochberg