Comparison of three different recombinant hepatitis B virus core particles expressed in Escherichia coli

Optimization of the expression of hepatitis B virus e gene in Pichia pastoris and immunological characterization of the product

Escherichia coli-derived hepatitis B e antigen (HBeAg) is widely used for serological tests of hepatitis B virus (HBV). Because it exhibits cross-reactivity with HBcAb in human sera, current antibody to HBeAg (HBeAb) immunoassays are based on competitive inhibition enzyme-linked immunosorbent assay (ELISA) rather than sandwich ELISA, which interfere with the specificity and sensitivity of HBeAb detection. Pichia pastoris has advantages of eukaryotic cells, while having the capacity of high-level secretion of foreign proteins. To explore the diagnostic suitability of recombinant HBeAg (rHBeAg), we expressed the wild type HBV e gene (wt-e-gene) and the synthetic HBV e gene (syn-e-gene; native HBV e gene modified based on synonymous codon usage bias) in P. pastoris. The recombinant antigen was secreted into the medium. The expression level of rHBeAg was enhanced by optimizing HBV e gene. The yield of syn-e-gene product was approximately five-fold greater than wt-e-gene. The protein represented 66% of the total supernatant protein, and was simply purified to 90%. P. pastoris-derived HBeAg showed high HBe antigenicity, while lacking any HBc antigenicity and cross-reactivity between all proteins derived from the culture of P. pastoris and normal human sera. P. pastoris-derived HBeAg has higher specificity and sensitivity for detection HBeAb in the diagnostic assay than the commercial HBeAb ELISA kits.

Gamma-adaptin, a novel ubiquitin-interacting adaptor, and Nedd4 ubiquitin ligase control hepatitis B virus maturation

Hepatitis B virus (HBV) budding from infected cells is a tightly regulated process that requires both core and envelope structures. Here we report that HBV uses cellular gamma2-adaptin and Nedd4, possibly in conjunction with ubiquitin, to coordinate its assembly and release. In search of interaction partners of the viral L envelope protein, we previously discovered gamma2-adaptin, a putative endosomal sorting and trafficking adaptor of the adaptor protein complex family. We now demonstrate that the viral core interacts with the same gamma2-adaptor and that disruption of the HBV/gamma2-adaptin interactions inhibits virus production. Mutational analyses revealed a hitherto unknown ubiquitin-binding activity of gamma2-adaptin, specified by a ubiquitin-interacting motif, which contributes to its interaction with core. For core, the lysine residue at position 96, a potential target for ubiquitination, was identified to be essential for both gamma2-adaptin-recognition and virus production. The participation of the cellular ubiquitin system in HBV assembly was further suggested by our finding that core interacts with the endosomal ubiquitin ligase Nedd4, partly via its late domain-like PPAY sequence. Overexpression of a catalytically inactive Nedd4 mutant diminished HBV egress, indicating that protein ubiquitination is functionally involved in virus production. Additional evidence for a link of HBV assembly to the endosomal machinery was provided by immunolabeling studies that demonstrated colocalization of core and L with gamma2-adaptin in compartments positive for the late endosomal marker CD63. Together, these data indicate that an enveloped DNA virus exploits a new ubiquitin receptor together with endosomal pathway functions for egress from hepatocytes.

Hepatitis B virus DNA-negative dane particles lack core protein but contain a 22-kDa precore protein without C-terminal arginine-rich domain

DNA-negative Dane particles have been observed in hepatitis B virus (HBV)-infected sera. The capsids of the empty particles are thought to be composed of core protein but have not been studied in detail. In the present study, the protein composition of the particles was examined using new enzyme immunoassays for the HBV core antigen (HBcAg) and for the HBV precore/core proteins (core-related antigens, HBcrAg). HBcrAg were abundant in fractions slightly less dense than HBcAg and HBV DNA. Three times more Dane-like particles were observed in the HBcrAg-rich fraction than in the HBV DNA-rich fraction by electron microscopy. Western blots and mass spectrometry identified the HBcrAg as a 22-kDa precore protein (p22cr) containing the uncleaved signal peptide and lacking the arginine-rich domain that is involved in binding the RNA pregenome or the DNA genome. In sera from 30 HBV-infected patients, HBcAg represented only a median 10.5% of the precore/core proteins in enveloped particles. These data suggest that most of the Dane particles lack viral DNA and core capsid but contain p22cr. This study provides a model for the formation of the DNA-negative Dane particles. The precore proteins, which lack the arginine-rich nucleotide-binding domain, form viral RNA/DNA-negative capsid-like particles and are enveloped and released as empty particles.

Puumala (PUU) hantavirus strain differences and insertion positions in the hepatitis B virus core antigen influence B-cell immunogenicity and protective potential of core-derived particles

Hepatitis B virus (HBV) core-derived chimeric particles carrying a Puumala (PUU) hantavirus (strain Vranica/Hällnäs) nucleocapsid (N) protein sequence (aa 1-45), alternatively inserted at three distinct positions (N-, C-terminus, or the internal region), and mosaic particles consisting of HBV core as well as core/PUU (Vranica/Hällnäs) N (aa 1-45) readthrough protein were generated. Chimeric particles carrying the insert at the N-terminus or the internal region of core induced some protective immune response in bank voles (Clethrionomys glareolus) against a subsequent PUU virus (strain Kazan) challenge; 40-50% of the animals showed markers of protection. In contrast, internal insertion of PUU strain CG18-20 N (aa 1-45) into the HBV core caused a highly protective immune response in the bank vole model. Immunizations with particles carrying aa 75-119 of PUU (CG18-20) N at the C-terminus of core verified the presence of a second, minor protective region in the N protein. A strong PUU N-specific antibody response was detected not only in bank voles immunized with chimeric particles containing internal and N-terminal fusions of PUU N protein but also in animals immunized with the corresponding mosaic particles. Except for the exclusive occurrence of antibodies directed against aa 231-240 of N in non-protected animals post virus challenge, there was no additional obvious difference in the epitope-specificity of N-specific antibodies from immunized animals prior and post virus challenge.

Core particles of hepatitis B virus as carrier for foreign epitopes

To be effective as vaccines, most monomeric proteins and peptides either require chemical coupling to high molecular weight carriers or application together with adjuvants. More recently, recombinant DNA techniques have been used to insert foreign epitopes into proteins with inherent multimerization capacity, such as particle-forming viral capsid or envelope proteins. The core protein of hepatitis B virus (HBcAg), because of its unique structural and immunological properties, has gained widespread interest as a potential antigen carrier. Foreign sequences of up to approximately 40 amino acid residues at the N terminus, 50 or 100 amino acids in the central immunodominant c/e 1 epitope region of HBcAg, and up to 100 or even more residues at the C terminus, did not interfere with particle formation. The humoral immunogenicity of inserted epitopes is determined by the immunogenicity of the peptide itself and its surface exposure, and is influenced by the route of application. The probably flexible and surface-exposed c/e1 region emerged as the most promising insertion site. When applied together with adjuvants approved for human and veterinary use, or even without adjuvants, such chimeric particles induced B and T cell immune responses against the inserted epitopes. In some cases neutralizing antibodies, cytotoxic T cells and protection against challenge with the intact pathogen were demonstrated. Major factors for the potentiated immune response against the foreign epitopes are the multimeric structure of chimeric HBcAg that results in a high epitope density per particle, and the provision of T cell help by the carrier moiety. Beyond its use as subunit vaccine, chimeric HBcAg produced in attenuated Salmonella strains may be applicable as live vaccine.

Chimaeric HBV core particles carrying a defined segment of Puumala hantavirus nucleocapsid protein evoke protective immunity in an animal model

Hantaviruses are rodent-born agents which are pathogenic in humans causing haemorrhagic fever with renal syndrome or hantavirus pulmonary syndrome. To induce a protective immunity against a European hantavirus (Puumala) we constructed chimaeric hepatitis B virus (HBV) core particles carrying defined fragments of the Puumala virus nucleocapsid protein. After immunisation of bank voles, the natural host of Puumala virus, with core particles possessing an insertion of the N-terminal part of Puumala virus nucleocapsid protein, four of five animals were protected against subsequent virus challenge. The results show that the major protective region of the nucleocapsid protein is located between amino acids 1 and 45 and that chimaeric HBV core-like particles are useful carriers of foreign protective epitopes.