A “Three-in-One” Photosynthesis System Harnessing the Synergistic Roles of Phycocyanobilin and Formate Dehydrogenase

Abstract The development of efficient and environmentally friendly strategies to emulate natural oxygenic photosynthesis remains a significant challenge. In particular, the identification of innovative raw materials with optimal light-harvesting and charge-transport properties is still limited. In this study, we evaluated phycocyanobilin (PCB), a previously unexplored chromophore, as a photosensitizer for artificial photosynthetic applications. Our investigation revealed that PCB-conjugated phycobiliproteins can effectively facilitate water splitting and NADH production under visible-light irradiation. To combine light capture with CO2 reduction, we genetically fused the allophycocyanin (APC) α-subunit, which covalently binds a single PCB chromophore molecule, to formate dehydrogenase (FDH), an NADH-dependent CO2 reducing enzyme, yielding a “three-in-one” artificial photosynthetic biocatalyst denoted as FDH-APC. Remarkably, the fusion enzyme catalyzed three core photosynthetic reactions, water splitting, CO2 reduction, and NADH regeneration under ambient aqueous conditions. Additionally, we solved the crystal structure of FDH-APC, validating the design at atomic resolution and providing mechanistic insights into its catalytic function. This work establishes a sustainable catalytic system that leverages an environmentally benign natural chromophore and protein engineering to advance the development of efficient artificial photosynthesis.