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Review
. 2018 Oct:46:196-202.
doi: 10.1016/j.cbpa.2018.08.009. Epub 2018 Sep 8.

Expansion of the genetic code via expansion of the genetic alphabet

Vivian T Dien  1 , Sydney E Morris  1 , Rebekah J Karadeema  1 , Floyd E Romesberg  2
Affiliations
Review

Expansion of the genetic code via expansion of the genetic alphabet

Vivian T Dien et al. Curr Opin Chem Biol. 2018 Oct.

Abstract

Current methods to expand the genetic code enable site-specific incorporation of non-canonical amino acids (ncAAs) into proteins in eukaryotic and prokaryotic cells. However, current methods are limited by the number of codons possible, their orthogonality, and possibly their effects on protein synthesis and folding. An alternative approach relies on unnatural base pairs to create a virtually unlimited number of genuinely new codons that are efficiently translated and highly orthogonal because they direct ncAA incorporation using forces other than the complementary hydrogen bonds employed by their natural counterparts. This review outlines progress and achievements made towards developing a functional unnatural base pair and its use to generate semi-synthetic organisms with an expanded genetic alphabet that serves as the basis of an expanded genetic code.

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Conflict of interest statement

Conflict of interest statement

Patent applications have been filed by Synthorx and The Scripps Research Institute covering the UBPs and their use to produce proteins containing ncAAs. F.E.R. also has shares in Synthorx, Inc., a company that has commercial interests in the UBP.

Figures

Figure 1.
Figure 1.
Base pairs. (a) The dNaM-d5SICS and dNaM-dTPT3 UBPs and a natural dG-dC pair (with complementary H-bonding shown). (b) The dCNMO-dTPT3 UBP. Phosphate and sugar moieties omitted for clarity.
Figure 2.
Figure 2.
Proposed mechanism of replication of DNA containing a UBP. The steps corresponding to unnatural triphosphate incorporation and extension are indicated. During synthesis within the DNA polymerase active site, the UBP adopts a Watson-Crick-like structure, but after translocation it is prone to intercalate, which hinders extension and requires de-intercalation. dX=dNaM and dY=dTPT3.
Figure 3.
Figure 3.
(a) SSO that replicates the UBP. (b) SSO that replicates and transcribes the UBP and decodes an unnatural codon to produce unnatural protein. X=NaM and Y=TPT3.
See this image and copyright information in PMC

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