Protein and Metabolic Engineering
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Evolving the Beta Roll Domain for Regulated Molecular Recognition
Self-assembly is an essential process for all forms of life. For example, proteins spontaneously fold into well-defined 3-dimensional structures, and cellular organelles form that spatially segregate diverse cellular processes. As engineers aim to create new devices and systems at ever decreasing size scales, self-assembly processes become increaseingly attactive techniques.
We are collaborating with Plamen Atanassov at University of New Mexico, Scott Calabrese-Barton at Michigan State University and Shelley Minteer at Saint Louis University to make improved electrodes for biofuel cells. In a biofuel cell, redox enzymes are immobilized on electrode surfaces. Enzymes located at the anode are able to oxidize substrates and the electrons move through an external circuit to create power. On the cathode, other redox enzymes are able to use the electrons to reduce oxygen to water. The net result of this process is the generation of electricity from a variety of readily available biofuel sources, with oxygen as the terminal electron acceptor.
The architecture of the electrodes is crucial for biofuel cell performance. The enzymes on the electrodes must be positioned so that electrons can easily move between the enzymatic active site and the electorde surface (Direct Electron Transfer (DET)). Alternatively, the enzymes can be immoblilized with redox mediators, such as osmium, that facilitate the transport of electrons from the electrodes to the enzymes (Fig. 1). In this Mediated Electron Transport (MET) configuration, the enzyme and mediators are immobilized in a polymer matrix on the electrode surface. While this system has been used to demonstrate impressive biofuel cell performances, it is potentially hampered by poor dispersion of the enzyme and mediator within the polymer matrix, and complex manufacturing requirments.
We are using biological self-assembly to improve the biofuel cell electrode construction and performance (Fig. 2). Instead of combing enzymes and mediators in a polymer matrix, we are creating self-assembling protein-based hydrogels that intrinsically include the redox enzymes and the mediators. In this configuration the loading of the enzyme and the mediators into the hydrogel can be finely controlled, and the hydrogel assembly process will be well-defined and repeatable. These new bioelectrocatalytic hydrogels will have the potential to significantly improve biofuel cell performance.