Liposome-Based in Vitro Evolution of Aminoacyl-tRNA Synthetase for Enhanced Pyrrolysine Derivative Incorporation

Methanosarcina species pyrrolysyl-tRNA synthetase (PylRS) attaches Pyl to its cognate amber suppressor tRNA. The introduction of two mutations (Y384F and Y306A) into PylRS was previously shown to generate a mutant, designated LysZ-RS, that was able to attach N-benzyloxycarbonyl-L-lysine (LysZ) to its cognate tRNA. Despite the potential of LysZ derivatives, further LysZ-RS engineering has not been performed; consequently, we aimed to generate LysZ-RS mutants with improved LysZ incorporation activity through in vitro directed evolution. Using a liposome-based in vitro compartmentalization (IVC) approach, we screened a randomly mutagenized gene library of LysZ-RS and obtained a mutant that showed increased LysZ incorporation activity both in vitro and in vivo. The ease and high flexibility of liposome-based IVC should enable the evolution of not only LysZ-RS that can attach various LysZ derivatives but also of other enzymes involved in protein translation.