Light-Driven CO₂ Reduction with a Surface-Displayed Enzyme Cascade–C₃N₄ Hybrid

Abstract

Efficient and cost-effective conversion of CO 2 to biomass holds the potential to address the climate crisis. Lightdriven CO 2 conversion can be realized by combining inorganic semiconductors with enzymes or cells. However, designing enzyme cascades for converting CO 2 to multicarbon compounds is challenging, and inorganic semiconductors often possess cytotoxicity. Therefore, there is a critical need for a straightforward semiconductor biohybrid system for CO 2 conversion. Here, we used a visible-light-responsive and biocompatible C 3 N 4 porous nanosheet, decorated with formate dehydrogenase, formaldehyde dehydrogenase, and alcohol dehydrogenase to establish an enzymephotocoupled catalytic system, which showed a remarkable CO 2to-methanol conversion efficiency with an apparent quantum efficiency of 2.48% in the absence of externally added electron mediator. To further enable the in situ transformation of methanol into biomass, the enzymes were displayed on the surface of Komagataella phaffii, which was further coupled with C 3 N 4 to create an organic semiconductor−enzyme−cell hybrid system. Methanol was produced through enzyme-photocoupled CO 2 reduction, achieving a rate of 4.07 mg/(L•h), comparable with reported rates from photocatalytic systems employing mediators or photoelectrochemical cells. The produced methanol can subsequently be transported into the cell and converted into biomass. This work presents a sustainable, environmentally friendly, and cost-effective enzyme-photocoupled biocatalytic system for efficient solardriven conversion of CO 2 within a microbial cell.

Revisiting Solar Energy Flow in Nanomaterial-Microorganism Hybrid Systems

“…308−312 Additionally, strategies for systematically optimizing energy flow in NMHSs utilizing energy carriers can be adopted in these cases, including the combination of surface-displayed enzymes and enhanced nanomaterial-cell adhesion. 359 Novel strategies, such as membraneless organelles and liquid−liquid phase separation techniques, can be applied to prokaryotic cells to confine target enzymes and/or nanomaterials within a limited intracellular space, effectively alleviating the physiological burden of overloading the cytoplasm with nanomaterials. 308−312 Optimizations for eukaryotic cells include analyzing the organelle localization profiles of nanomaterials, increasing the expression of target enzymes in specific organelles, and conferring nanomaterials with organelle-targeting capability through surface decoration.…”

“…Typically, nanomaterials can be subjected to surface decoration to enhance their intracellular accumulation in microbial cells, as well as their affinities and specificities toward target enzymes; microbial cells can be engineered to enhance their tolerance toward increased levels of intracellular QDs. Energy matching between QDs (E CB ) and target enzymes (redox potentials), and microbe’s tolerance against the toxicities of intracellular QDs, are factors to be further optimized. − Additionally, strategies for systematically optimizing energy flow in NMHSs utilizing energy carriers can be adopted in these cases, including the combination of surface-displayed enzymes and enhanced nanomaterial-cell adhesion . Novel strategies, such as membraneless organelles and liquid–liquid phase separation techniques, can be applied to prokaryotic cells to confine target enzymes and/or nanomaterials within a limited intracellular space, effectively alleviating the physiological burden of overloading the cytoplasm with nanomaterials. − Optimizations for eukaryotic cells include analyzing the organelle localization profiles of nanomaterials, increasing the expression of target enzymes in specific organelles, and conferring nanomaterials with organelle-targeting capability through surface decoration.…”