The influence of N-glycosylation and C-terminal sequence on secretion of HBV large surface antigen from S. cerevisiae

In Saccharomyces cerevisiae, we synthesized and secreted L-HBVsAg (named as pre-S(Met1 to Asn174)::S(Met175 to Ile400)) and three mutants, i.e., pre-S ^○○::S (Asn15Gln and Asn123Gln), pre-S^○○:: S^○ (Asn15Gln, Asn123Gln, and Asn320Gln), and pre-S ^○○::S^○○ (Asn15Gln, Asn123Gln, Asn233Gln, and Asn320Gln). All of the secreted pre-S::S was N-glycosylated, i.e., hyper-mannosylated. In the secretion of pre-S^○○::S and pre-S^○○::S^○, besides the hyper-mannosylated form, another immunoreactive protein with much lower molecular mass was observed, which seems to be unglycosylated form of pre-S^○○::S and pre-S^○○::S^○. Only a part of the secreted pre-S^○○::S or pre-S^○○::S^○ molecules was N-glycosylated, and the site for the partial N-glycosylation seems to be Asn233 in S-antigen region. Compared to the N-glycosylated pre-S ^○○::S and pre-S^○○::S^○, pre-S^○○::S^○○ (non-N-glycosylated mutant) was secreted with lower secretion efficiency but showed apparent immunoreactivity to anti-S antigen monoclonal Ab. Interestingly, unlike pre-S^○○::S^○○ with authentic C-terminus, the recombinant pre-S^○○::S^○○ with C-terminal myc or poly-histidine tag (pre-S^○○::S ^○○::tag) was almost all aggregated into insoluble proteins in the intracellular region. Conclusively, the C-terminal sequence and glycosylation in S-antigen region seem to be of crucial importance in determining the secretion efficiency of L-HBVsAg in S. cerevisiae.