Rational Design of a Miniature Photocatalytic CO₂-Reducing Enzyme

Abstract

Photosystem I (PSI) is a very large membrane protein complex (∼1000 kDa) harboring P700*, the strongest reductant known in biological systems, which is responsible for driving NAD(P) + and ultimately for CO 2 reduction. Although PSI is one of the most important components in the photosynthesis machinery, it has remained difficult to enhance PSI functions through genetic engineering due to its enormous complexity. Inspired by PSI's ability to undergo multiple-step photo-induced electron hopping from P700* to iron−sulfur [Fe 4 S 4 ] clusters, we designed a 33 kDa miniature photocatalytic CO 2 -reducing enzyme (mPCE) harboring a chromophore (BpC) and two [Fe 4 S 4 ] clusters (Fe A /Fe B ). Through reduction potential fine-tuning, we optimized the multiple-step electron hopping from BpC to Fe A /Fe B , culminating in a CO 2 / HCOOH conversion quantum efficiency of 1.43%. As mPCE can be overexpressed with a high yield in Escherichia coli cells without requiring synthetic cofactors, further development along this route may result in rapid photo-enzyme quantum yield improvement and functional expansion through an efficient directed evolution process. KEYWORDS: photosystem I, rational design, photosensitizer protein, iron−sulfur (Fe 4 S 4 ) cluster, photocatalytic, CO 2 reductase

Artificial photosynthesis systems for solar energy conversion and storage: platforms and their realities

“…144 Afterward, they developed a miniature photocatalytic CO 2 -reducing enzyme (mPCE) by replacing the Ni-terpyridine complex with a genetically fused ferredoxin containing two [Fe 4 S 4 ] clusters in the PSP loop region. 191 Under light irradiation, the photochemically reduced chromophore was able to reduce the [Fe 4 S 4 ] clusters, indicating its competency for efficient CO 2 reduction. After optimizing the reduction potential, this APS could continuously operate with a CO 2 /HCOOH conversion QE of 1.43%, which was much higher than most of the previous APS's that drove the CO 2 -reducing enzymes by heavy metal-containing photosensitizers.…”

“…Taking the APS's based on the platform for synergistic catalysis as an example, the overall coupling of electron donor oxidation, electron transfer, and biocatalysis in this platform leads to the high photon-product conversion efficiency, especially for APS's with intraprotein electron transport chains. 183,191 However, the poor stability of proteins under extreme conditions seriously hampers its extensive application in the APS's platform. A promising strategy to enhance its availability is to exploit an ideal carrier that can integrate with biocatalysts and complete oxidoreductase activation efficiently at a low cost.…”

Photobiocatalysis for Abiological Transformations

“…Using this strategy, Wang and co-workers installed benzophenone-alanine genetically into the superfolder yellow fluorescent protein and conjugated a nickel-terpyridine complex for the photocatalytic reduction of CO 2 (Figure B) . By using site-directed mutagenesis, they tuned the position of the chromophore and catalyst, modulated the photochemical properties of the photosensitizer, and adjusted the microchemical environment of the protein for more efficient CO 2 reduction . In another study, Wu, Liu, Zhong, Wang, and co-workers modified the previous photoactive protein to an artificial dehalogenase that consists of a genetically encoded benzophenone chromophore and an adjacent artificial Ni II (bpy) cofactor (Figure C) .…”

“…57 By using site-directed mutagenesis, they tuned the position of the chromophore and catalyst, modulated the photochemical properties of the photosensitizer, and adjusted the microchemical environment of the protein for more efficient CO 2 reduction. 58 In another study, Wu, Liu, Zhong, Wang, and co-workers modified the previous photoactive protein to an artificial dehalogenase that consists of a genetically encoded benzophenone chromophore and an adjacent artificial Ni II (bpy) cofactor (Figure 5C). 59 In this study, energy-transfer activation was proposed to facilitate the reductive elimination step, thereby accomplishing crosscouplings of aryl halides.…”

A Review on the Bioinspired Photocatalysts and Photocatalytic Systems

“…A bioinspired photocatalytic system constructed by controlled assembly of light-harvesting plasmonic nanoantennas onto butterfly wings' 3D architectures [11] has been achieved based on adopting nature's far red-to-NIR responsive architectures. In addition, artificial photocatalysts can also be obtained by utilizing or simulating the molecular structures of active components those play important roles in natural photosynthesis, such as enzymes [12,13] and porphyrin. [14] Significant development progress of the bioinspired plasmonic photocatalysts, such as antireflective surfaces, 3D photonic structures and branched structures in the past decade was discussed.…”