Engineering a Polyspecific Pyrrolysyl-tRNA Synthetase by a High Throughput FACS Screen

The Pyrrolysyl-tRNA synthetase (PylRS) and its cognate tRNA(Pyl) are extensively used to add noncanonical amino acids (ncAAs) to the genetic code of bacterial and eukaryotic cells. However, new ncAAs often require a cumbersome de novo engineering process to generate an appropriate PylRS/tRNA(Pyl) pair. We here report a strategy to predict a PylRS variant with novel properties. The designed polyspecific PylRS variant HpRS catalyzes the aminoacylation of 31 structurally diverse ncAAs bearing clickable, fluorinated, fluorescent, and for the first time biotinylated entities. Moreover, we demonstrated a site-specific and copper-free conjugation strategy of a nanobody by the incorporation of biotin. The design of polyspecific PylRS variants offers an attractive alternative to existing screening approaches and provides insights into the complex PylRS-substrate interactions.