Advances of bioelectrocatalysis by oxidoreductases

Abstract

<p indent=0mm>Bioelectrocatalysis attracts much attention with the advantages of high selectivity, high efficiency, no byproduct and environmental friendliness. Electrification of industrial biotechnology is challenging for the different operating conditions and catalysts of electrochemical and biochemical reactions. In this review, we present the state-of-the-art information on enzymatic electrosynthesis for the production of fine chemicals. Multidisciplinary strategies of electrode surface modification and enzyme immobilization have been integrated in electrocatalytic devices with various applications in biosensors and bioelectrocatalysis. However, the efficiency of bioelectrosynthesis is determined by the intramolecular electron transfer rate, and interfacial electron transfer rate between the oxidoreductases and electrode. This review aims to summarize recent progresses on the mechanism studies of intramolecular electron transferof redox proteins, including tunneling, hopping, proton-coupled electron transfer, etc. Modular origin of electron transfer chain was also discussed from the perspective of the evolution of spatial adjacency network. Novel and efficient oxidoreductases with enhanced intramolecular and interfacial electron transfer rate can be obtained by protein engineering. The strategies for facilitating intramolecular electron transfer are addressed, which includes the regulation of co-evolved electron transfer network, the designs of molecular switch and the assembly of conductive modules. Oxidoreductases are engineered to improve their biocatalytic performance by using the tools of molecular evolution, modeling, structure prediction, and mutation. Co-evolved molecular switches controll proton-coupled electron transfer and regulate electron transfer inside the multi-center redox proteins. Assembly of surface-binding conductive peptides to oxidoreductases facilitates electricity-driven catalysis. Moreover, the modifications of oxidoreductases allow their predictable immobilization on functionalized electrode surface with improved stability, controlled orientation, surface coverage and enhanced electron transfer. After that, electron transfer within a series of well-defined peptides with orientation-controlled and surface-confined enzymes was addressed. Strategies also developed to increase the biocompatible active surface of electrodes and to promote charge transfer reactions. Nano- and macroporous electrodes based on metal nanoparticles, nanocarbon tubes, graphene, and metallic inverse opals have been designed and fabricated with predictable surface functionalities and electrochemical properties. Electrode/mediator/cofactor/enzyme conjugates can enhance the <italic>in vitro</italic> bioelectricity generation of cofactor. Screening of redox mediators for electrochemical regeneration of NADH was also summarized. Multifunctional surfaces of nano or meso-porous electrodes, where oxidoreductases were bounded to structured electrodes with necessary components (e.g., mediators, cofactor, etc.) with tailored properties, were summarized. Optimizations of functional electrode materials and surfaces can improve the efficiency of cofactor regeneration in the electrochemical reactor modules. Key challenges and future research for better bioelectrocatalysis are discussed and expected briefly. Mining and engineering of novel and robust enzymes from genomic and metagenomic libraries would benefit the bioelectrocatalysis. Based on genome mining, discovery of novel oxidoreductases from extreme microorganism provide thermophilic, alkalophilic, halophilic and organic solvent tolerant oxidoreductases. Reactors for bioelectrocatalysis are optimized to provide a platform for the production of chiral chemicals, which brings great promises for biomanufacturing. Further study of bio-inspired multi-enzyme immobilization which mimics quick electron transfer in multi-enzyme complex is suggested. A variety of approaches for bioelectrocatalysis have been successfully applied for the synthesis of chiral chemicals which are intermediates of fine chemicals and pharmaceuticals. Bioelectrosynthesis processes could replace many chemically catalyzed routes in the future, and aims to construct a new platform for more efficient and green biomanufacturing.