In a groundbreaking study conducted at the Tokyo Institute of Technology, researchers have harnessed the power of in-cell engineering to create hybrid solid catalysts with exceptional catalytic properties. These catalysts, derived from protein crystals, show immense promise for artificial photosynthesis and offer potential solutions for sustainable energy production. The research, published recently in Nano Letters, opens new doors for the synthesis of functional materials using environmentally friendly techniques.

Protein crystals, much like conventional crystals, boast well-ordered molecular structures that hold immense potential for customization and diverse properties. What sets them apart is their natural ability to self-assemble from cellular materials, reducing synthesis costs and environmental impact significantly.

However, current methodologies limit the attachment of only small molecules and basic proteins to these crystals, leaving vast untapped potential in the realm of enzyme immobilization. To address this limitation, the Tokyo Tech research team, led by Professor Takafumi Ueno, devised an innovative strategy that merges in-cell engineering with a straightforward in vitro process to produce hybrid solid catalysts geared for artificial photosynthesis.

The foundation of these groundbreaking catalysts lies in a protein monomer derived from a virus that infects silkworms. By introducing the gene responsible for this protein into Escherichia coli bacteria, the researchers prompted the formation of trimers, which spontaneously assembled into stable polyhedra crystals (PhCs) via their N-terminal α-helix (H1) interactions. The team then took it a step further by introducing a modified version of the formate dehydrogenase (FDH) gene from yeast, leading to the production of FDH enzymes with H1 terminals. This, in turn, gave rise to the remarkable hybrid H1-FDH@PhC crystals within the bacterial cells.

Through an ingenious extraction process involving sonication and gradient centrifugation, the team successfully retrieved the hybrid crystals from E. coli bacteria. The next step involved soaking the crystals in a solution containing eosin Y (EY), an artificial photosensitizer. The genetically modified protein monomers, equipped with a central channel capable of hosting EY molecules, facilitated the stable binding of EY to the hybrid crystals, yielding substantial quantities of the complex.

The results were nothing short of remarkable. The team achieved the production of highly active, recyclable, and thermally stable EY·H1-FDH@PhC catalysts, capable of converting carbon dioxide (CO2) into formate (HCOO−) upon exposure to light, effectively mimicking the process of photosynthesis. Even after immobilization, these catalysts retained an impressive 94.4% of their catalytic activity compared to that of the free enzyme. "The conversion efficiency of the proposed hybrid crystal was an order of magnitude higher than that of previously reported compounds for enzymatic artificial photosynthesis based on FDH," emphasized Prof. Ueno. Furthermore, the hybrid PhC retained its solid protein assembly state after undergoing both in vivo and in vitro engineering processes, showcasing the remarkable crystallizing capacity and strong plasticity of PhCs as encapsulating scaffolds.

The study highlights the immense potential of bioengineering in the synthesis of complex functional materials. The seamless integration of in vivo and in vitro techniques for encapsulating protein crystals promises an effective and eco-friendly approach for research in nanomaterials and artificial photosynthesis.

This groundbreaking research offers hope for a greener future, presenting innovative solutions that could pave the way for sustainable energy production and reduced environmental impact.