An In Vivo Method for Biotinylation of Recombinant Variola Virus Proteins

This work implements a method for specific in vivo biotinylation of recombinant proteins M1 and B7 of the variola virus during biosynthesis in CHO-K1 cells. To do this, co-expression of the biotin ligase BirA and target genes encoding the ectodomains of the M1 and B7 proteins with a C-terminal avi-tag was carried out in CHO-K1 cells in the presence of biotin in the culture medium. The optimal biotin concentration for the expression of the M1 and B7 proteins was 125 μM. The production of biotinylated recombinant proteins has been complicated by low yields. To increase the production of target proteins, low molecular weight enhancers were added to the culture medium: lithium acetate, sodium valproate, and caffeine. The enhancers increased the yield of the target protein by 1.3–4.9 times and did not affect the efficiency of biotinylation. The highest yield of biotinylated protein was achieved with the simultaneous addition of a concentration of 10 mM lithium acetate and 2.5 mM sodium valproate.