Efficient incorporation of p-azido-l-phenylalanine into the protein using organic solvents

Azide, the most used photo-crosslinking group, facilitates the analysis of protein structure and function. This group is particularly useful when photochemically label antibodies and examine protein-protein interactions. The use of the expanded genetic code technique allows the special labeling of the functional azide group in proteins by adding the unnatural amino acid (UAA), p-azido-l-phenylalanine (AzF), in response to the amber codon during translation. However, a low UAA uptake rate due to mass transfer resistance in the cell membrane may lead to the early termination of the full-length protein. This study reports a general method for the efficient in vivo incorporation of AzF into the target protein by improving cell permeability using organic solvents. As expected, the yield of the full-length protein was significantly increased, which indicated that the AzF uptake was greatly improved due to the addition of organic solvents. Our method can serve as a good reference for improving the genetic incorporation of other kinds of UAAs into proteins.