Abstract
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.
Highlights
Biofuel cells are electrochemical devices that use enzymatic reactions to catalyze the conversion of chemical energy to electricity in a fuel cell
The electrosome is composed of two compartments: (i) a hybrid anode, which consists of dockerin-containing enzymes attached 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
We have designed a novel yeast surface-display system displaying different scaffoldin proteins in order to improve the performance of hybrid biofuel cells
Summary
Biofuel cells are electrochemical devices that use enzymatic reactions to catalyze the conversion of chemical energy to electricity in a fuel cell. The oxygen-reducing enzymes laccase and bilirubin oxidase were coupled to the anode, and a fully hybrid biofuel cell was developed [8]. Another advantage of enzyme surface-display is that the laborious and time-consuming purification processes of enzymes were avoided and the surface-displayed redox enzymes were site- wired to an electrode to further improve electron transfer, as described by Amir et al [9], who used the Escherichia coli (E. coli) autodisplay system [10] for the display of alcohol dehydrogenase (ADH) as the anodic reaction catalyst. Hybrid biofuel cells of yeast displaying different hydrogenases on the same surface were presented [13]
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