J. Le Seyec et al., Infection process of the hepatitis B virus depends on the presence of a defined sequence in the pre-S1 domain, J VIROLOGY, 73(3), 1999, pp. 2052-2057
During the life cycle of hepatitis B virus (HBV), the large envelope protei
n (L) plays a pivotal role. Indeed, this polypeptide is essential for viral
assembly and probably for the infection process. By performing mutagenesis
experiments, we have previously excluded a putative involvement of the pre
-S2 domain of the L protein in viral infectivity. In the present study, we
have evaluated the role of the pre-S1 region in HBV infection. For this pur
pose, 21 mutants of the L protein were created. The entire pre-S1 domain wa
s covered by contiguous deletions of 5 amino acids. First, after transfecti
on into HepG2 cells, the efficient expression of both glycosylated and ungl
ycosylated L mutant proteins was verified. The secretion rate of envelope p
roteins was modified positively or negatively by deletions, indicating that
the pre-S1 domain contains several regulating sequences able to influence
the surface protein secretion. The ability of mutant proteins to support th
e production of virions was then studied. Only the four C-terminal deletion
s, covering the 17 amino acids suspected to interact with the cytoplasmic n
ucleocapsids, inhibited virion release. Finally, the presence of the modifi
ed pre-S1 domain at the external side of all secreted virions was confirmed
, and their infectivity was assayed on normal human hepatocytes in primary
culture. Only a short sequence including amino acids 78 to 87 tolerates int
ernal deletions without affecting viral infectivity. These results confirm
the involvement of the L protein in the infection step and demonstrate that
the sequence between amino acids 3 and 77 is involved in this process.