Cracking the Code: Reprogramming the Genetic Script in Prokaryotes and Eukaryotes to Harness the Power of Noncanonical Amino Acids

Over 500 natural
and synthetic amino acids have been genetically
encoded in the last two decades. Incorporating these noncanonical
amino acids into proteins enables many powerful applications, ranging
from basic research to biotechnology, materials science, and medicine.
However, major challenges remain to unleash the full potential of
genetic code expansion across disciplines. Here, we provide an overview
of diverse genetic code expansion methodologies and systems and their
final applications in prokaryotes and eukaryotes, represented by Escherichia coli and mammalian cells as the main
workhorse model systems. We highlight the power of how new technologies
can be first established in simple and then transferred to more complex
systems. For example, whole-genome engineering provides an excellent
platform in bacteria for enabling transcript-specific genetic code
expansion without off-targets in the transcriptome. In contrast, the
complexity of a eukaryotic cell poses challenges that require entirely
new approaches, such as striving toward establishing novel base pairs
or generating orthogonally translating organelles within living cells.
We connect the milestones in expanding the genetic code of living
cells for encoding novel chemical functionalities to the most recent
scientific discoveries, from optimizing the physicochemical properties
of noncanonical amino acids to the technological advancements for
their in vivo incorporation. This journey offers
a glimpse into the promising developments in the years to come.