CHAPTER 4: Investigating Heme Enzymes with Expanded Genetic Codes

Heme enzymes have attracted lots of attention due to their significance in physiology and potential application in synthetic chemistry. Genetic code expansion has become a powerful technique in protein engineering in recent years. It also has wide applications in heme protein studies. Many site-specific incorporated probes have been reported for heme protein structural studies, including nuclear magnetic resonance (NMR) probes, spin probes and infrared probes. Together with newly developed spectroscopic methods, structure information which cannot be gained using traditional methods has been revealed. Meanwhile, genetically encoded unnatural amino acids with novel chemical properties have brought about new opportunities in heme enzyme design and optimization, such as the precise design of the coordination environment, and tuning of the steric and redox properties of the protein scaffold. Site-specific immobilization based on genetically encoded "click" probes has shown potential application in enzyme electrocatalysis, which is crucial for the large-scale synthetic application of heme enzymes. With continuous progress in both genetic code expansion methods and heme enzyme studies, inspiring achievements are expected in the future.