Unnatural Amino Acid Mediated Protein Bioorthogonal Labeling

The bioorthogonal chemistry has become a valuable tool for specific labeling of biomolecules in living systems. One emerging example is to convert the palladium-mediated carbon-carbon bond formation reaction, a landmark reaction in organic synthesis, into the biocompatible reaction for biomolecule modifications. A prerequisite to enable such reactions to be executed on biological samples is to incorporate the corresponding bioorthogonal functional groups into target biomolecules. The genetic code expansion strategy is a leading technology on introducing diverse bioorthogonal functionalities into proteins, and the most recently developed pyrrolysine system can now allow unnatural amino acids (UAAs) bearing bioorthogonal handles into proteins in prokaryotic cells, etikaryotic cells and even in living animals. In this perspective, we will first introduce some of the forefronts of the bioorthognal reactions as well as the genetic code expansion strategy. We then will discuss the advantages and attractiveness of combining these newly emerged tools, Pd-mediated biomolecular labeling and pyrrolysine-based genetic code expansion system in particular, to specifically label and study proteins in living mammalian cells. More biocompatible reactions and more flexible UAA incorporation system will significantly strengthen and expand our ability to specifically manipulate proteins in their native cellular environment.