Structure of pre-S2 N- and O-linked glycans in surface proteins from different genotypes of hepatitis B virus

1 Institute of Biochemistry, University of Giessen, Friedrichstrasse 24, D-35392 Giessen, Germany 2 Institute of Medical Virology, University of Giessen, Frankfurter Strasse 107, D-35392 Giessen, Germany Correspondence Wolfram H. Gerlich Wolfram.H.Gerlich{at}viro.med.uni-giessen.de The middle-sized (M) surface proteins of hepatitis B virus (HBV) and other orthohepadnaviruses contain a conserved N -glycan in their pre-S2 domain, which is essential for the secretion of viral particles. Recently, we also found O -glycans in the pre-S2 domain of M protein from woodchuck hepatitis virus (WHV) and HBV genotype D. Since the O -glycosylation motif is not conserved in all genotypes of HBV, the glycosylation patterns of HBV genotypes A and C were analysed. Pre-S2 (glyco)peptides were released from HBV-carrier-derived HBV subviral particles by tryptic digestion, purified by reversed-phase HPLC and identified by amino acid and amino-terminal sequence analysis as well as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Pre-S2 N -glycans were characterized by anion-exchange chromatography, methylation analysis and on-target sequential exoglycosidase digestions in combination with MALDI-TOF-MS, demonstrating the presence of partially sialylated diantennary complex-type oligosaccharides in all genotypes examined. Pre-S2 O -glycans were characterized by on-target sequential exoglycosidase digestions in combination with MALDI-TOF-MS. The pre-S2 domain of M protein and, to a minor extent, of L (large) protein from HBV genotype C and D was partially O -glycosylated by Neu5Ac( 2–3)Gal( 1–3)GalNAc - or Gal( 1–3)GalNAc -units at Thr-37 within a conserved sequence context. Genotype A, containing no Thr at position 37 or 38, was not O -glycosylated. Analytical data further revealed that M protein is mostly amino-terminally acetylated in all examined genotypes and that the terminal methionine is partially oxidized. The findings may be relevant for the secretion and the immunogenicity of HBV. Additional experiments are supplied as supplementary data, available in JGV Online.