Differences in the post-translational modifications of human papillomavirus type 6b major capsid protein expressed from a baculovirus system comparedwith a vaccinia virus system

Virus-like particles (VLPs) are being currently investigated in vaccines ag ainst viral infections in humans. There are different recombinant-protein-e xpression systems available for obtaining the necessary VLP preparation for vaccination. However, the differences in post-translational modifications of the recombinant proteins obtained and their differences in efficacy in e liciting an anti-viral response in vaccines are not well established. In th is study we have compared the posttranslational modifications of human papi llomavirus type-6b major capsid protein L1 (HPV 6bL1) expressed using recom binant baculovirus (rBV) in Sf9 (Spodoptera frugiperda) insect cells, with the protein expressed using recombinant vaccinia virus (rVV) in CV-1 kidney epithelial cells, Two-dimensional gel electrophoresis of biosynthetically labelled rBV-expressed HPV 6bL1 showed several post-translationally modifie d variants of the protein, whereas rVV-expressed HPV 6bL1 showed only a few variants. Phosphorylations were detected at threonine and serine residues for the L1 expressed from rBV compared with phosphorylation at serine resid ues only for the L1 expressed from rVV. HPV 6bL1 expressed using rBV incorp orated [H-3]mannose and [H-3]galactose, whereas HPV 6bL1 expressed using rV V incorporated only [H-3]galactose. We conclude that post-translational mod ification of recombinant HPV 6bL1 can differ according to the system used f or its expression. Since recombinant L1 protein is a potential human-vaccin e candidate, the implication of the observed differences in post-translatio nal modifications on immunogenicity of L1 VLPs warrants investigation.