Laboratory study demonstrates an engineered bacterial tyrosyl-tRNA synthetase platform for expanding mammalian genetic codes, enabling incorporation of diverse noncanonical amino acids.
High Resolution Image Download MS PowerPoint Slide The Escherichia coli tyrosyl-tRNA synthetase (EcTyrRS)/tRNA EcTyr pair offers an attractive platform for genetically encoding new noncanonical amino acids (ncAA) in eukaryotes. However, challenges associated with a eukaryotic selection system, which is needed to engineer the platform, have impeded its success in the past. Recently, using a facile E. coli -based selection system, we showed that EcTyrRS could be engineered in a strain where the endogenous tyrosyl pair was substituted with an archaeal counterpart. However, significant cross-reactivity between the UAG-suppressing tRNA CUA EcTyr and the bacterial glutaminyl-tRNA synthetase limited the scope of this strategy, preventing the selection of moderately active EcTyrRS mutants. Here we report an engineered tRNA CUA EcTyr that overcomes this cross-reactivity. Optimized selection systems based on this tRNA enabled the efficient enrichment of both strongly and weakly active ncAA-selective EcTyrRS mutants. We also developed a wide dynamic range (WiDR) antibiotic selection to further enhance the activities of the weaker first-generation EcTyrRS mutants. We demonstrated the utility of our platform by developing several new EcTyrRS mutants that efficiently incorporated useful ncAAs in mammalian cells, including photoaffinity probes, bioconjugation handles, and a nonhydrolyzable mimic of phosphotyrosine.
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Grasso et al. (2022) studied this question.
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