Optimization of genetic code expansion in the baculovirus expression vector system (BEVS)

The production of recombinant proteins containing unnatural amino acids, commonly known as genetic code expansion (GCE), represents a breakthrough in protein engineering that allows for the creation of proteins having novel designed properties. The naturally occurring orthogonal pyrrolysine tRNA/aminoacyl-tRNApyl synthetase pair (tRNApyl/PylRS) found in Methanosarcinaceae species has provided a rich platform for protein engineers to build a library of amino acid derivatives suitable for the introduction of novel chemical functionalities. While reports of the production of such recombinant proteins utilizing the tRNApyl/PylRS pair, or mutants thereof, is commonplace in Escherichia coli and mammalian cell expression systems, there has only been a single such report of GCE in the other stalwart of recombinant protein production, the baculovirus expression vector system (BEVS). However, that report formulates protein production within the designs of the MultiBac expression system [1]. The current study frames protein production within the strategies of the more commonplace Bac-to-Bac system of recombinant baculovirus production, via the development of novel baculovirus transfer vectors that harbor the tRNApyl/PylRS pair. The production of recombinant proteins harboring an unnatural amino acid(s) was examined using both an in cis and an in trans arrangement of the tRNApyl/PylRS pair relative to the target protein ORF i.e. the latter resides, respectively, on either the same vector as the tRNApyl/PylRS pair, or on a separate vector and deployed in a viral co-infection experiment. Aspects of the transfer vector designs and the viral infection conditions were investigated.