Ser/Leu-swapped cell-free translation system constructed with natural/in vitro transcribed-hybrid tRNA set

The Ser/Leu-swapped genetic code can act as a genetic firewall, mitigating biohazard risks arising from horizontal gene transfer in genetically modified organisms. Our prior work demonstrated the orthogonality of this swapped code to the standard genetic code using a cell-free translation system comprised of 21 in vitro transcribed tRNAs. In this study, to advance this system for protein engineering, we introduce a natural / in vitro transcribed-hybrid tRNA set. This set combines natural tRNAs from Escherichia coli (excluding Ser, Leu, and Tyr) and in vitro transcribed tRNAs, encompassing anticodon-swapped tRNA Ser GAG and tRNA Leu GGA . This approach reduces the number of in vitro transcribed tRNAs required from 21 to only 4. In this optimized system, the production of a model protein, superfolder green fluorescent protein, increases to 3.5-fold. With this hybrid tRNA set, the Ser/Leu-swapped cell-free translation system will stand as a potent tool for protein production with reduced biohazard concerns in future biological endeavors. The use of orthogonal genetic code can help to prevent the escape of hazardous genes through horizontal gene transfer. Here, the authors develop a cell-free translation system with the Ser/Leu-swapped genetic code using a hybrid tRNA set and show its application in enhancing the production of superfolder GFP.