Residues critical for duck hepatitis B virus neutralization are involved in host cell interaction

To date, no detailed analysis of the neutralization properties of duck hepatitis B virus (DHBV) has been reported, and it is not clear whether any of the known neutralization epitopes correspond to the viral receptor binding site or to sequences involved in the cell entry pathway. We demonstrate here that antibodies directed against two overlapping peptides (amino acids 83 to 97 and 93 to 107), covering the sequences of most DHBV pre-S neutralizing epitopes, both inhibit virus binding to primary duck hepatocytes and neutralize virus infectivity. An extensive mutagenesis of the motif 88WTP90, which is the shortest sequence of the epitope recognized by the virus-neutralizing monoclonal antibody (MAb) 900 was performed in order to define the amino acids involved in these interactions. Single point mutations within this epitope affected neither virus replication nor infectivity but abolished virus neutralization by MAb 900 completely. Interestingly, mutants with two and three consecutive residue replacements (SIP and SIH) within this epitope retained replication competence but were no longer infectious. The loss of infectivity of SIH and SIP mutant particles was associated with significantly reduced binding to primary duck hepatocytes and could be rescued by trans complementation with wild-type pre-S protein. Taken together, these results indicate that each amino acid of the DHBV pre-S sequence 88WTP90 is critical for recognition by the neutralizing MAb 900 and that replacement of the first two or all three residues strongly reduces virus interaction with hepatocytes and abrogates infectivity. These data imply that the motif 88WTP90 contains key residues which are critical for interaction with both the neutralizing MAb and the host cell.