A short sequence within domain C of duck carboxypeptidase D is critical for duck hepatitis B virus binding and determines host specificity

Virus-cell surface receptor interactions are of major interest. Hepadnaviru ses are a family of partially double-stranded DNA viruses with liver tropis m and a narrow host range of susceptibility to infection. At least in the c ase of duck hepatitis B virus (DHBV), host specificity seems controlled par tly at the receptor level. The middle portion in the pre-S region of the vi ral large envelope protein binds specifically to duck carboxypeptidase D (D CPD) but not to its human or chicken homologue. Although domain C of DCPD i s implicated in ligand binding, the exact pre-S contact site remains to be determined. We prepared and tested a panel of chimeric constructs consistin g of DCPD and human carboxpeptidase D (HCPD). Our results indicate that a s hort region at the N terminus of domain C (residues 920 to 949) is critical to DHBV binding and is a major determinant for the host specificity of DHB V infection. Replacing this region of the DCPD molecule with its human homo logue abolished the DHBV interaction, whereas introducing this DCPD sequenc e into HCPD conferred efficient DHBV binding. Extensive analysis of site-di rected mutants revealed that both conserved and nonconserved residues were important for the pre-S interaction. There were primary sequence variations and secondary structural differences that contributed to the inability of HCPD to bind the DHBV pre-S domain.