Mutational profiling of the variability of individual amino acid positions in the hepatitis B virus matrix domain.

The hepatitis B virus (HBV) is formed by budding. A stretch of 22 amino acids (aa) (matrix domain, MD, R103 - S124) in the large envelope protein L is crucial for virion formation and probably establishes contact to the nucleocapsid. Here, we assess the impact of sequence variations at numerous individual aa positions within the MD on virion formation. We generated panels of L mutants covering all 19 possible aa for 11 positions and tested the capacity of these mutants to rescue virus production by an L-defective HBV genome. At four positions (L112, R113, P117, W122), any replacement of the wild type (WT) aa reduced virus assembly to undetectable levels. Virus production was strongly diminished by substitutions at five other positions (R103, T106, S115, H116, A119). Only two tested positions (D114, Q118) tolerated several substitutions. The restricted positions may represent promising targets for the development of novel antiviral strategies.

Characterization of West Nile virus live vaccine candidates attenuated by capsid deletion mutations.

Protein C deletion mutants of West Nile virus (WNV) were evaluated for their potential use as live virus vaccine candidates in vivo. Double and triple mutants carrying small deletions and second-site point mutations, as well as mutants with large deletions of 36 and 37 amino acid residues were tested in a stringent mouse challenge model. The mutant viruses were found to be non-pathogenic and to induce protective immunity in a wide range of inoculation doses (10(1)-10(6)FFU). Furthermore, the effects of combining three different previously identified resuscitating point mutations, as well as the combination of a large protein C deletion with a deletion mutation in the 3' non-coding region were studied. The data indicate that the production of safe and efficacious WNV live vaccines based on protein C deletion mutations is feasible.

Helices alpha2 and alpha3 of West Nile virus capsid protein are dispensable for assembly of infectious virions.

The internal hydrophobic sequence within the flaviviral capsid protein (protein C) plays an important role in the assembly of infectious virions. Here, this sequence was analyzed in a West Nile virus lineage I isolate (crow V76/1). An infectious cDNA clone was constructed and used to introduce deletions into the internal hydrophobic domain which comprises helix alpha2 and part of the loop intervening helices alpha2 and alpha3. In total, nine capsid deletion mutants (4 to 14 amino acids long) were constructed and tested for virus viability. Some of the short deletions did not significantly affect growth in cell culture, whereas larger deletions removing almost the entire hydrophobic region significantly impaired viral growth. Efficient growth of the majority of mutants could, however, be restored by the acquisition of second-site mutations. In most cases, these resuscitating mutations were point mutations within protein C changing individual amino acids into more hydrophobic residues, reminiscent of what had been observed previously for another flavivirus, tick-borne encephalitis virus. However, we also identified viable spontaneous pseudorevertants with more than one-third of the capsid protein removed, i.e., 36 or 37 of a total of 105 residues, including all of helix alpha3 and a hydrophilic segment connecting alpha3 and alpha4. These large deletions are predicted to induce formation of large, predominantly hydrophobic fusion helices which may substitute for the loss of the internal hydrophobic domain, underlining the unrivaled structural and functional flexibility of protein C.