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Cartoon diagram of an enzyme molecule immobilized on an electrode surface. Covalent attachment can be used to promote stable binding in the correct orientation for efficient electron transfer from the electrode to the redox site in the protein, such as electron relay centers or the active site. Redox active noncanonical amino acids (e.g. DOPA) incorporated into proteins will serve as essential components in designing redox enzyme active sites and relays between the electrode and enzyme active site for multiple-step electron transfer. Exmaple of protein immobilization through a C-terminal cysteine residue
Enzyme immobilization issues
Work to be done: Optimization of electrode immobilization techniques for DET (direct electron transfer)
Metal-containing cofactors, protein residues of tryptophan, tyrosine, or cysteines may also act as electron relays, in e.g., ribonucleotide reductase, photosystem II, DNA photolyase, and cytochrome c/cytochrome c peroxidase MCR-2 is one of the shortest natural c-type cytochromes known today (23 amino-acids long), thus could be used to achieve DET
Protein electron relays
Cytochrome c (right) was fused to glucose dehydrogenase (left) and provide natural minimal ET domain via a short polypeptide linker. electron relay module Protein with redox center Heering, H. A., Weiner, J. H. & Armstrong, F. A. Direct Detection and Measurement of Electron Relays in a Multicentered Enzyme: Voltammetry of Electrode-Surface Films of E. coli Fumarate Reductase, an Iron−Sulfur Flavoprotein. J. Am. Chem. Soc.119,11628–11638 (1997). Heering, H. A., Wiertz, F. G. M., Dekker, C. & de Vries, S. Direct Immobilization of Native Yeast Iso- 1 Cytochrome c on Bare Gold: Fast Electron Relay to Redox Enzymes and Zeptomole Protein-Film Voltammetry. J. Am. Chem. Soc. 126, 11103 – 11112 (2004). A New Type of Electron Relay Station in Proteins: https://pubs.acs.org/doi/abs/10.1021/jp512628x
