THE GDPAL REGION OF THE PRE-S1 ENVELOPE PROTEIN IS IMPORTANT FOR MORPHOGENESIS OF WOODCHUCK HEPATITIS-VIRUS

The pre-S envelope protein of duck hepatitis B virus (DHBV) contains a region, Asp-Asp-Pro-Leu-Leu (DDPLL), that is specifically required fo r virus assembly and secretion (Lenhoff and Summers, J Virol 1994;68:4 565-4571). We found that amino acids 201 to 205 of the pre-S envelope protein of woodchuck hepatitis virus (WHV) form a conserved amino acid cluster, Gly-Asp-Pro-Ala-Leu (GDPAL), which resembles the DDPLL seque nce of DHBV, To determine whether the GDPAL region was functionally eq uivalent to the DDPLL region, we deleted this region from the pre-S pr otein of WHV or mutated individual amino acids within the region. The mutant DNA was transfected into human hepatoma cell line Huh7, and the medium was assayed for virion production by immunoprecipitation and S outhern blot analysis. We found that an in-frame deletion of this smal l region inhibited virion formation, suggesting that the GDPAL region of the pre-S envelope protein was required for virus assembly and/or s ecretion of WHV. Individual replacement of alanine 204, leucine 205, o r serine 206 with other amino acid residues did not affect virus produ ction. However, substitution of either aspartic acid 202 with valine o r proline 203 with leucine dramatically inhibited WHV production. Furt hermore, the GDPAL mutants were individually tested for their abilitie s to complement a pre-S1 defective genome. The results showed that the GDPAL region functioned as part of the pre-S1 protein but was not req uired to function as part of the pre-S2 protein.