Development of SpyTag/SpyCatcher-Bacmid Expression Vector System (SpyBEVS) for Protein Bioconjugations Inside of Silkworms.

Protein conjugations at post-translational levels are known to be essential to protein stability and function. Recently, it has been proven that the split protein CnaB2 (SpyTag/SpyCatcher, ST/SC) from Streptococcus pyogenes can induce covalent conjugation rapidly and efficiently under various conditions. The protein of interest fused with the split protein SC/ST could be assembled spontaneously. In light of this finding, we introduced the ST/SC protein coupling concept into the silkworm-bacmid protein expression system (SpyBEVS). As a proof of concept, we first examined and confirmed that a competent ligation occurred between ST/SC-fused protein partners in vitro in cultured silkworm cells and in vivo in silkworm larvae by co-infection of several recombinant baculoviruses. The protein conjugation could be also achieved sufficiently by a simple one-step mixture of purified ST/SC-tagged peptide-protein pairs in vitro. Given the flexibility and robustness of silkworm-BEVS, our results on SpyBEVS show an alternative method for enabling the production of protein decorations in vitro and inside of silkworms.