Expanding the Genetic Code of Bioelectrocatalysis and Biomaterials

Genetic code expansion is a promising genetic engineering technology that incorporates noncanonical amino acids into proteins alongside the natural set of 20 amino acids. This enables the precise encoding of non-natural chemical groups in proteins. This review focuses on the applications of genetic code expansion in bioelectrocatalysis and biomaterials. In bioelectrocatalysis, this technique enhances the efficiency and selectivity of bioelectrocatalysts for use in sensors, biofuel cells, and enzymatic electrodes. In biomaterials, incorporating non-natural chemical groups into protein-based polymers facilitates the modification, fine-tuning, or the engineering of new biomaterial properties. The review provides an overview of relevant technologies, discusses applications, and highlights achievements, challenges, and prospects in these fields.

Encapsulation of Microorganisms, Enzymes, and Redox Mediators in Graphene Oxide and Reduced Graphene Oxide

Graphene oxide (GO) and reduced graphene oxide (rGO) were demonstrated in the past decade as biocompatible carbon-based materials that could be efficiently used in bioelectrochemical systems (BESs). Specifically, for redox enzyme encapsulation in order to improve electron communication between enzymes and electrodes. The addition of GO to different solvents was shown to cause gelation while still allowing small molecule diffusion through its gel-like matrix. Taking the combination of these traits together, we decided to use GO hydrogels for the encapsulation of enzymes displayed on the surface of yeast in anodes of microbial fuel cells. During our studies we have followed the changes in the physical characteristics of GO upon encapsulation of yeast cells displaying glucose oxidase in the presence of glucose and noted that GO is being rapidly reduced to rGO as a function of glucose concentrations. GO reduction under these conditions served as a proof of electron communication between the surface-displayed enzymes and GO. Hence, we set out to study this phenomenon by the encapsulation of a purified glucose dehydrogenase (in the absence of microbial cells) in rGO where improved electron transfer to the electrode could be observed in the presence of phenothiazone. In this chapter, we describe how these systems were technically constructed and characterized and how a very affordable matrix such as GO could be used to electrically wire enzymes as a good replacement for expensive mediator containing redox active polymers commonly used in BESs.

The Electrosome: A Surface-Displayed Enzymatic Cascade in a Biofuel Cell's Anode and a High-Density Surface-Displayed Biocathodic Enzyme

The limitation of surface-display systems in biofuel cells to a single redox enzyme is a major drawback of hybrid biofuel cells, resulting in a low copy-number of enzymes per yeast cell and a limitation in displaying enzymatic cascades. Here we present the electrosome, a novel surface-display system based on the specific interaction between the cellulosomal scaffoldin protein and a cascade of redox enzymes that allows multiple electron-release by fuel oxidation. The electrosome is composed of two compartments: (i) a hybrid anode, which consists of dockerin-containing enzymes attached specifically to cohesin sites in the scaffoldin to assemble an ethanol oxidation cascade, and (ii) a hybrid cathode, which consists of a dockerin-containing oxygen-reducing enzyme attached in multiple copies to the cohesin-bearing scaffoldin. Each of the two compartments was designed, displayed, and tested separately. The new hybrid cell compartments displayed enhanced performance over traditional biofuel cells; in the anode, the cascade of ethanol oxidation demonstrated higher performance than a cell with just a single enzyme. In the cathode, a higher copy number per yeast cell of the oxygen-reducing enzyme copper oxidase has reduced the effect of competitive inhibition resulting from yeast oxygen consumption. This work paves the way for the assembly of more complex cascades using different enzymes and larger scaffoldins to further improve the performance of hybrid cells.