Expressed protein modifications: Making synthetic proteins

Techniques to manipulate cellular gene expression such that amino acid analogs not encoded by the genetic code are incorporated into a polypeptide chain have recently gained increasing interest. The so-called noncanonical amino acids often have unusual properties that can be translated into target proteins by reprogrammed ribosomal protein synthesis. Residue-specific substitution of a specific canonical amino acid by its analogs provokes global effects in the resulting protein congeners that include improved stability or catalytic activity, reduced redox sensitivity, as well as altered spectral properties. Thus, the approach holds great promise for the engineering of synthetic proteins. This contribution describes a protocol for the incorporation of a noncanonical amino acid into a target protein expressed in an appropriate amino acid auxotrophic E. coli strain.