The periodically aligned amino acid residues of protein crystals allow for comprehensive structural analysis and site-specific modification, which are essential features in the research of protein immobilization, solid catalysts, X-ray crystallography, and hybrid materials.1 Even though the engineering of protein crystals has been studied via physicochemical and genetic routes,2 the current encapsulation systems of protein crystals are limited to either exogenous small molecules or monomeric proteins. Thus, the potential of protein crystals to contain both natural enzymes and synthetic functional molecules has not been fully explored, and these “hybrid” protein crystals could offer great opportunities for promoting complicated reactions involving multiple modules such as photosynthesis.
In this study, we constructed an enzyme-coupled artificial photosynthesis system based on hybrid protein crystals. First, the internal space and electrostatic potential of polyhedra crystal (PhC) were engineered to encapsulate both the enzyme and the small guest molecule. Second, formate dehydrogenase from Candida boidinii (cbFDH) and the photosensitizer eosin Y (EY) were incorporated in PhC by in-cell co-assembly and soaking methods, respectively. Eventually, the engineered protein crystals maintained the in-cell self-assembly capacity, and the hybridization of natural enzyme and synthetic photosensitizer yielded competing photosynthesis activity and thermal stability. This immobilization method greatly simplifies the purification of FDH and maintains 94.4% catalytic activity compared to the free enzyme. Moreover, the recyclable and thermal stable features of the solid catalyst would lower the cost of NADH-dependent productions.
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