Genetic code expansion (GCE) is the ability to encode polypeptide building blocks beyond the standard 20 the ribosome uses for protein translation, known as nonstandard amino acids (nsAAs). The broadening of chemical functionalities in proteins produced by live cells has generated substantial value across fundamental and applied research settings. However, a common limitation of GCE approaches is their reliance on the supplementation of chemically synthesized nsAAs to cell culture media. To overcome this limitation of nsAA sourcing, efforts have engineered systems for nsAA biosynthesis, often in the same host that performs GCE. In recent years, these works have reported new chemical targets obtained through biosynthesis, as well as additional rationale for combining metabolic engineering and GCE, particularly for synthetic biology applications. Here, we review this rapidly advancing field and provide our perspectives on technical and conceptual innovations.
Wyllis et al. (2026) studied this question.