Free radicals for post-translational modification

In the effort to find new methods to diagnose and cure diseases, scientists have turned their attention to post-translational modifications of proteins – adding functional groups or other proteins to a protein freshly produced from its genetic instructions. Post-translational modifications alter the properties of the original proteins, which can greatly expand their structures and functions, and regulate cell activity and reaction sites. For example, adding one or more units of the protein ubiquitin to other proteins plays an important role in regulating the occurrence, development and metastasis of several cancers.

In nature, the cell’s protein modification process has been refined by millions of years of evolution, but only works for natural amino acids. Chemical techniques to achieve specific modifications without restrictions face certain challenges. Firstly, the reaction needs to be carried out in the water phase, since the protein is often only soluble in water. Secondly, the chemical reaction conditions must be mild enough to avoid protein inactivation. Thirdly, the chemical reactions need to be reasonably selective, because proteins often have many functional groups with different properties. Therefore, the application of site-specific biomolecule modification is more restricted, and at this early stage of development is mainly limited to peptides, not whole proteins.