CHARACTERIZATION OF EARLY HEPATITIS-B VIRUS SURFACE PROTEIN OLIGOMERS

The small surface protein (S) of the hepatitis B virus (HBV) is synthe sized as unglycosylated p24 and N-glycosylated gp27 and forms disulfid e linked dimers. Former models proposed that these complexes consist p referentially of p24-gp27 heterodimers. Furthermore, cell free in vitr o experiments suggested that p24 has a transmembrane topology differen t from gp27. We tested these models by expressing the HBV surface prot eins in transfected cell cultures and characterizing early maturation products after short pulse labelings. Two dimensional unreduced-reduce d polyacrylamide gel electrophoresis demonstrated that p24 and gp27 di merized without preference for a specific pairing. Protease protection experiments showed that both, p24 and gp27, had identical transmembra ne topologies in cell culture. The middle sized (M) and large HBV surf ace proteins formed mixed dimers with the S protein. Mutant M and S pr otein in which all 10 cysteine residues in the ectodomain and transmem brane regions were replaced by serine residues formed no intermolecula r S-S bridges but were secreted like wild type M and S protein.