"Cold" Orthogonal Translation: Psychrophilic Pyrrolysyl-tRNA Synthetase as Efficient Tool for Expanding the Genetic Code

Using orthogonal translation systems (OTSs) is one of the most efficient strategies for producing unnatural proteins through the incorporation of non-canonical amino acids (ncAAs) into the genetic code. Traditionally, efforts to expand substrate specificity start with a (hyper-)stable enzyme capable of withstanding the structural changes induced by necessary mutations. In contrast, we propose a radically different approach for the PylRS system: by starting with enzymes that evolved to cope with instability in order to adapt to cold conditions, potentially offering greater resilience to mutational changes. By finding and further engineering a psychrophilic ("cold") OTS from Methanococcoides burtonii, we developed an alternative to the widely used mesophilic and thermophilic systems. This novel OTS demonstrated exceptional in vivo efficiency for a broad range of substrates, even at very low ncAA concentrations and low cultivation temperatures. The general versatility of the PylRS system across a wide range of applicable host organisms suggests that the Cold-OTS has the potential to also improve protein yields in these hosts and help to drive the transformation of the expanded genetic code from an academic pursuit into a high-value, chemistry-driven biotechnology.