Localization on the viral genome and nucleotide sequence of the gene coding for the two major polypeptides of the hepatitis B surface antigen (HBs Ag)

Hepatitis B Virus Epsilon (ε) RNA Element: Dynamic Regulator of Viral Replication and Attractive Therapeutic Target

Hepatitis B virus (HBV) chronically infects millions of people worldwide, which underscores the importance of discovering and designing novel anti-HBV therapeutics to complement current treatment strategies. An underexploited but attractive therapeutic target is ε, a cis-acting regulatory stem-loop RNA situated within the HBV pregenomic RNA (pgRNA). The binding of ε to the viral polymerase protein (P) is pivotal, as it triggers the packaging of pgRNA and P, as well as the reverse transcription of the viral genome. Consequently, small molecules capable of disrupting this interaction hold the potential to inhibit the early stages of HBV replication. The rational design of such ligands necessitates high-resolution structural information for the ε-P complex or its individual components. While these data are currently unavailable for P, our recent structural elucidation of ε through solution nuclear magnetic resonance spectroscopy marks a significant advancement in this area. In this review, we provide a brief overview of HBV replication and some of the therapeutic strategies to combat chronic HBV infection. These descriptions are intended to contextualize our recent experimental efforts to characterize ε and identify ε-targeting ligands, with the ultimate goal of developing novel anti-HBV therapeutics.

Virtual Screening of Hepatitis B Virus Pre-Genomic RNA as a Novel Therapeutic Target

The global burden imposed by hepatitis B virus (HBV) infection necessitates the discovery and design of novel antiviral drugs to complement existing treatments. One attractive and underexploited therapeutic target is ε, an ~85-nucleotide (nt) cis-acting regulatory stem-loop RNA located at the 3'- and 5'-ends of the pre-genomic RNA (pgRNA). Binding of the 5'-end ε to the viral polymerase protein (P) triggers two early events in HBV replication: pgRNA and P packaging and reverse transcription. Our recent solution nuclear magnetic resonance spectroscopy structure of ε permits structure-informed drug discovery efforts that are currently lacking for P. Here, we employ a virtual screen against ε using a Food and Drug Administration (FDA)-approved compound library, followed by in vitro binding assays. This approach revealed that the anti-hepatitis C virus drug Daclatasvir is a selective ε-targeting ligand. Additional molecular dynamics simulations demonstrated that Daclatasvir targets ε at its flexible 6-nt priming loop (PL) bulge and modulates its dynamics. Given the functional importance of the PL, our work supports the notion that targeting ε dynamics may be an effective anti-HBV therapeutic strategy.

Peculiarities in the designations of hepatitis B virus genes, their products, and their antigenic specificities: a potential source of misunderstandings

The nomenclature of the hepatitis B virus (HBV) genes and their products has developed stepwise, occasionally in an erratic way, creating many misunderstandings, especially among those who do not know the structure of HBV and its genome in detail. One of the most frequent misunderstandings, even presented in leading journals, is the designation of HBV “e”-antigen as envelope or early antigen. Another problem area are the so-called “pre” regions in the HBV genome present upstream of both the core and the surface genes of HBV, inadvertently suggesting that they may be a part of corresponding precursor proteins. Misnomers and misclassifications are frequent in defining the subgenotypes and serological subtypes of HBV. Even the well-established terminology for HBV surface (HBs) or HBV core (HBc) antigen deviates from the conventional virological nomenclature for viral envelopes or capsid proteins/antigens, respectively. Another matter of undesirable variability between publications is the numbering of the nucleotides and the graphical representation of genomic maps. This editorial briefly explains how the nomenclature evolved, what it really means, and suggests how it could be adapted to today’s knowledge.

Biotechnology and the transformation of vaccine innovation: The case of the hepatitis B vaccines 1968-2000

The approval, from 1986, of a series of recombinant hepatitis B vaccines was a landmark both in the growth of biotechnology and in the development of the vaccine innovation system. In this paper, we show how the early development of the hepatitis B vaccines was shaped by a political and economic context that newly favoured commercialisation of academic research, including the appropriation and management of intellectual property; we elucidate the contingent interests and motivations that led new biotechnology companies and established pharmaceutical businesses to invest in developing recombinant vaccines specifically against hepatitis B; and we show how these and other factors combined to make those vaccines an unexpected commercial success. Broadening the scope of our analysis to include not just North America and Europe but also low- and middle-income countries, we show how the development of the hepatitis B vaccines facilitated the emergence of a two-tier innovation system structured by tensions between the demands for commercial profitability on the one hand, and the expectation of public health benefit for low- and middle-income countries on the other.

Prophylactic vaccination against hepatitis B: achievements, challenges and perspectives

Large-scale vaccination against hepatitis B virus (HBV) infection started in 1984 with first-generation vaccines made from plasma of chronic carriers containing HBV surface antigen (HBsAg). Thereafter, it was replaced in most countries by second-generation vaccines manufactured in yeast cells transformed with gene S encoding HBsAg. Both generations of vaccines have been applied for universal neonate and early childhood vaccination worldwide and have led to a 70-90 % decrease in chronic HBV carrier rates. However, 10-30% of newborns from HBsAg/HBeAg-positive mothers cannot be protected by passive/active vaccination alone and become chronic HBV carriers themselves. Asymptomatic occult HBV infections are frequent even in those who have protective levels of anti-HBs. Suboptimal protection may be due to heterologous HBsAg subtypes that are present in 99% of HBV carriers worldwide. Second-generation vaccines contain partially misfolded HBsAg and lack preS1 antigen that carries the major HBV attachment site and neutralizing epitopes. Third-generation vaccines produced in mammalian cells contain correctly folded HBsAg and neutralizing epitopes of the preS antigens, induce more rapid protection, overcome nonresponse to second-generation vaccines and, most importantly, may provide better protection for newborns of HBV-positive mothers. PreS/S vaccines expressed in mammalian cells are more expensive to manufacture, but introduction of more potent HBV vaccines should be considered in regions with a high rate of vertical transmission pending assessment of health economics and healthcare priorities. With optimal vaccines and vaccination coverage, eradication of HBV would be possible.

Immunogenic comparison for two different recombinant chimeric peptides (CP12 and CP22) containing one or two copies of three linear B cell epitopes from β-hCG subunit

To develop a superior chimeric peptide (CP) vaccine of human chorionic gonadotropin (hCG), two CP antigens (named CP12 and CP22) encoding one or two copies of three linear B cell epitopes from the β-hCG subunit and six foreign T cell epitopes, including two promiscuous TCEs from hepatitis B surface antigen and tetanus toxoid, were constructed and biosynthesized. The hCG CP12 and CP22 of 21 or 23 kDa, respectively, were expressed in Escherichia coli at the level of ~1% of total cell proteins when inserted into thermo-inducible pBV221 expression vector. The purified CP12 and CP22 proteins with >95% relative homogeneity are immunogenic, and elicited antibodies against the β5, β9 and β8 BCEs of β-hCG in both rabbits and three different inbred strains of mice. A mouse uterine weight study in Balb/c mice demonstrated that the CP12 and CP22 antigens with an additional β5 neutralizing epitope enhanced the in vivo bio-neutralization capacity of the induced antibodies compared to the C-terminal immunogen of β-hCG. We propose that the biosynthesized CP22, possessing with two copies of three BCEs, represents a novel candidate antigen for an hCG contraceptive or tumor therapeutic vaccine.

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Molecular epidemiological features of pre-pre-S region in hepatitis B virus genome

AIM: To try to identify pre-pre-S region in hepatitis B virus (HBV) genome and to study the relationship between the genotype and the existence of pre-pre-S region.

METHODS: Genomic DNA of HBV was extracted from the sera of patients with HBV infection. Multiple-primers polymerase chain reaction (PCR) method was used to identify the genotype of HBV strains. Then the pre-pre-S region was amplified by PCR method, and TA cloned into pGEM Teasy vector. After sequencing of the target region, vector 8.0 software was used to analyse the sequences.

RESULTS: Fifteen male patients were collected in this study. There were 1 genotype B, 5 genotype B and C mixture, and 9 genotype C. Amplified PCR products of the pre-pre-S region from these 15 samples were ligated into the pGEM Teasy vectors. After sequencing, 31 clones were found being encoding for pre-pre-S peptide.

CONCLUSION: Existence of coding gene of the pre-pre-S region is popular in B or C genotype of HBV.

Molecular epidemiological features of pre-X region in hepatitis B virus genome

AIM: To identify pre-X region in hepatitis B virus (HBV) genome and to study the relationship between the genotype and the existence of pre-X region.

METHODS: HBV genomic DNA was extracted from the sera of patients with HBV infection. Multiple-primers polymerase chain reaction (PCR) method was used to identify the genotype of HBV strains. Pre-X region was amplified by PCR method, and TA cloning technique was used to clone the DNA fragment into pGEM Teasy vector. After sequencing of the target region, Vector 8.0 software was used to analysis the sequences.

RESULTS: Seventeen samples were collected in this study. One genotype A, 3 genotype B, 10 genotype C and 3 B/C genotype mixture were identified. After sequencing, 27 clones from 45 clones (60%) were found encoding the pre-X peptide. Eighteen from 27 clones (66.7%) pre-X coding sequences were found from C genotype. Three types of replacement mutation led to pre-mature coding of pre-X gene. The mutation in pre-X peptide had feature of individually mutation.

CONCLUSION: Coding of the pre-X gene is popular in HBV genome.

Identification and characterization of high variable regions in hepatitis B virus genome of adr and adw serotypes

AIM: To identify a hypervariable region or a hyperconservative region in hepatitis B virus (HBV) genome and to study the pre-X region and the pre-pre-S region.

METHODS: Full-length of HBV genomes deposited in GenBank were searched and compared for their identity and homology. According to their sequences, the HBV genomes of adr or adw serotypes were selected. The Vector 6.0 software was used to compare the identity and difference among the strains of HBV genomes.

RESULTS: Twenty-eight strains of HBV genome in GenBank belong to adr serotype HBV genome, and 22 strains belong to adw serotype. After being compared, the total identity rates were 76.6% and 73.9%, respectively. There might be a hypervariable region and a hyperconservative region in adr serotype HBV genome, with the regional identity rate of 54.5% and 92.1%, respectively. There might be a hyperconservative region in adw serotype HBV genome, with the regional identity rate of 85.0%. Region coding pre-pre-S gene was popular in the strains. Pre-X region might be a serotype-specific gene. A²⁶⁰⁸ C/T and/or C/A²⁷³³ T replacement mutation resulted in disability of coding pre-X gene.

CONCLUSION: There may be a hyperconservative region in HBV genome. Pre-pre-S gene and pre-X gene are worthy of further study.

Study on definition of pre-x region in hepatitis B virus genome

AIM

To identify the pre-X gene in HBV strains of Chinese patients.

METHODS

The whole HBV genome was amplified by long-distance and accurate polymerase chain reaction (LA-PCR) method from the serum of 2 patients with chronic HBV infection, and then the PCR products were cloned into pGEM Teasy vectors. Five clones of HBV genome were sequenced. Sequences of our finding were compared with other HBV genome sequence deposited in GenBank.

RESULTS

Pre-X region was found in the HBV genome of these 5 clones, just upstream to the X gene. The pre-X gene is 168 bp long, and can be translated with X gene in frame. The amino acids sequence of pre-X gene was as the following: MGLGYWPSPPAWNLCGSSADPYCGTPSSLFCS QPVWSETYRNRQLCCPLSQIHLLS.

CONCLUSION

Pre-X region may be a serotype-specific coding gene.

Study on definition of pre-pre-S region in hepatitis B virus genome

AIM

To investigate the new open reading frame (ORF) in hepatitis B virus (HBV) genome.

METHODS

The whole HBV genome was amplified by long-distance and accurate polymerase chain reaction (LA-PCR) method from the serum of 2 patients with chronic HBV infection, and then the PCR products were ligased into pGEM Teasy vectors. Five clones of HBV genome were sequenced. Sequences of our finding were compared with other HBV genome sequence deposited in GenBank.

RESULTS

A new ORF was found in HBV genome, just before Pre-S1 region. It was defined as pre-pre-S region. The pre-pre-S ORF was deduced to be translated with Pre-S1, Pre-S2 and S gene in frame. Its amino acids sequence was as the following: MQLIITSKLGIIYILCGRLVFYIREKLHAV PHFVGHHILGNKSYS. There was a TA-rich region before the ATG of pre-pre-S ORF, indicating a possible promoter for its transcription.

CONCLUSION

There is a new ORF pre-pre-S located upstream to pre-S1 region.

Molecular mimicry of hepatitis B surface antigen by an anti-idiotype-derived synthetic peptide

Monoclonal antibody 2F10 is an "internal-image" anti-idiotype (anti-id) antibody capable of mimicking the group-specific "a" determinant of human hepatitis B surface antigen (HBsAg). By mRNA sequencing and computer-assisted molecular modeling of monoclonal antibody 2F10, we identified a 15-amino acid region of the heavy-chain hypervariable region that has partial residue homology with sequences of the "a" determinant epitopes of HBsAg. We have established that a linear 15-mer peptide from a contiguous region on the anti-id antibody can (i) generate anti-HBsAg-specific antibodies when injected into mice, (ii) prime murine lymph node cells for in vitro HBsAg-specific T-cell proliferative responses, and (iii) stimulate in vitro human CD4+ T cells that were primed in vivo to HBsAg by natural infection with hepatitis B virus or vaccination with a commercially available HBsAg vaccine. Significantly, this peptide could also stimulate CD4+ T cells of human hepatitis B virus carriers. We conclude that a 15-mer peptide derived from the anti-id sequence can duplicate the B- and T-cell stimulatory activity of the intact anti-id antibody and the antigen that is mimicked, HBsAg.

Identification of the hepatitis B virus factor that inhibits expression of the beta interferon gene

The identity of the trans-acting factor encoded by the 1,828-bp BamHI DNA fragment of hepatitis B virus (HBV) that suppresses the transcription of the human beta interferon gene was investigated. Each complete and partial open reading frame (ORF) present within the 1,828-bp BamHI HBV DNA fragment was cloned into a simian virus 40 expression vector, and the resulting gene products were assayed for their ability to inhibit the activity of the regulatory DNA region that governs the expression of the beta interferon gene. Only the proteins encoded by the C ORF inhibited the activity of the beta interferon regulatory DNA region; putative proteins encoded by the partial X, P, and S ORFs present in the 1,828-bp BamHI HBV DNA fragment had no effect. A plasmid encoding only the native HBV core antigen, but not one coding for a truncated core antigen, possessed this inhibitory activity. The inhibition by the core antigen was specific for the regulatory elements of the beta interferon gene; none of a variety of viral transcriptional elements was inhibited.

An internal domain of the hepatitis B virus X antigen is necessary for transactivating activity

A number of deletion mutants of the hepatitis B viral X antigen had been constructed and assayed for their ability to transactivate heterologous viral regulatory elements. Neither the N-terminal nor the C-terminal amino acid residues were required for transactivating activity. Transactivating activity that resided within amino acid residues 32 to 148 of the X antigen did not show any target DNA sequence or cell line specificity.

Transcriptional activation of the human immunodeficiency virus type 1 long terminal repeat by hepatitis B virus X-protein requires de novo protein synthesis

Human hepatitis B virus (HBV) X-gene, previously shown to be capable of trans-activating heterologous regulatory elements of the human beta-interferon gene, the human immunodeficiency virus type I (HIV-1) long terminal repeat (LTR), the simian virus 40 (SV40), and HBV, has the capacity to code for a 17-kDa polypeptide (designated pX17). We now report that pX17 synthesized in Escherichia coli can activate transcription controlled by the HIV-1 LTR using a protoplast fusion technique. Protoplasts of E. coli-containing presynthesized X-protein were fused with lymphocytic H938 cells harboring an integrated copy of a plasmid with the CAT gene under control of the HIV-1 LTR (HIV-1 LTR CAT) and a marked increase in the steady state expression of the CAT mRNA was observed. When the same fused cells were treated with the protein synthesis inhibitor cyclohexamide, the pX17-dependent activation of the HIV-1 LTR was abolished. This result indicates that the X-protein expressed in E. coli is biologically active and suggests that the HBV X-protein-mediated trans-activation of the HIV-1 LTR in this system requires de novo cellular protein synthesis.

Hepatitis B virus (HBV) X gene expression in human cells and anti-HBx antibodies detection in chronic HBV infection

All mammalian hepatitis B virus genomes contain an open reading frame X (X-ORF) of unknown function which could encode a protein of 17 kDa. Using a plasmid containing the entire X-ORF preceded by the adenovirus type 2 major late promoter and its tripartite leader sequence efficient expression of the HBV X-gene was achieved. The X protein of 17 kDa was characterized by immunoblotting and immunoprecipitated with an antiserum prepared against a X fusion protein produced in E. coli. By cell fractionation and indirect immunofluorescence the X-protein was found at least in part associated with nuclei. Human cell extracts containing the X protein have been used to screen human sera for anti-HBx antibodies. Such antibodies were detected in sera from patients with active chronic hepatitis with ongoing viral replication. The efficient expression of the HBV X protein obtained will facilitate its functional analysis.

Transcription of the human beta interferon gene is inhibited by hepatitis B virus

The manner by which the trans-acting factor encoded by the 1,828-base-pair (bp) BamHI DNA fragment of hepatitis B virus (HBV) suppresses the production of human beta interferon was determined. Steady-state levels of RNA specific for human beta interferon were decreased in cells that contained the 1,828-bp BamHI DNA fragment of HBV. The reduced accumulation of interferon-specific RNA was due to an inhibition of transcription of the interferon gene by the HBV trans-acting moiety. The expression of the interferon gene that is under the control of a heterologous promoter such as the simian virus 40 early promoter was not altered by the presence of the 1,828-bp BamHI HBV DNA fragment. In contrast, the HBV moiety inhibited the expression of the cat gene, whose expression is controlled by the regulatory DNA region of the human beta interferon gene. These results indicate that the HBV trans-acting moiety suppresses the expression of the human beta interferon gene at the transcriptional level by interacting with the regulatory DNA sequences 5' to the coding sequences for beta interferon.

Frequent detection of antibodies to hepatitis B virus x-protein in acute, chronic and resolved infections

Recombinant MS2- or beta gal fusion proteins containing parts of hepatitis B virus (HBV) HBx-, HBc-, and HBs-amino acid sequences were expressed in Escherichia coli and were used to screen 96 and 60 serum samples of HBV infected and uninfected patients, respectively, for the corresponding antibodies by immunoblotting. Antibodies against HBx were detected in 20 out of 65 sera of patients with previous resolved HBV-infection, in 3 out of 7 patients with persistent infection, and in 9 out of 24 sera of patients with acute HBV infection. The specificity of the immune reaction was confirmed by competition experiments with MS2- and beta gal-HBx fusion proteins, and by the lack of HBx antibodies in the sera of uninfected patients. Hbs and HBc antibodies were detected less frequently by immunoblotting with recombinant fusion proteins than by a commercial immunoassay. Our results indicate that HBx antibodies are induced early and frequently during HBV infection suggesting that the HBx protein is an early antigenic protein expressed in vivo.

Transcriptional trans-activating function of hepatitis B virus

The ability of hepatitis B virus (HBV) to stimulate the expression of a cellular gene was investigated by using a transient-expression system. A plasmid in which the expression of the bacterial chloramphenicol acetyltransferase (cat) gene had been placed under the control of the DNA sequences that regulate the expression of the human beta-interferon gene was constructed. In Vero cells, cotransfection of the 2.7-kilobase BglII DNA fragment of HBV together with the test plasmid containing the cat gene resulted in stimulation of the expression of the cat gene. This HBV DNA fragment was specific in its trans-activation; no significant stimulation of CAT activity was observed in constructs when the promoter and enhancer elements were derived from the murine sarcoma viral long terminal repeat, Rous sarcoma virus, BK virus, or simian virus 40. Results of subcloning of the HBV DNA fragment indicate that the trans-activating function resides in a 944-base-pair EcoRV-BglII DNA fragment of the HBV genome that contains the X structural gene and its promoter element. Removal of the promoter from the X structural gene resulted in loss of the trans-activating function. A frameshift mutation within the X gene region also eliminated the trans-activating activity. These results suggest that the X antigen could play a role in HBV infections by activating the expression of cellular genes.

Immunological cross-reactivity between preS2 sequences of the hepatitis B virus envelope proteins corresponding to serological subtypes adw2 and ayw

An immune response to epitopes localized on the preS region of the hepatitis B virus (HBV) envelope (env) is elicited during recovery from HBV infection and appears to play a role in virus clearance. Anti-preS antibodies (Ab) are expected to be protective against HBV infection as indicated by the virus-neutralizing capacity of Ab to a preS2-specific synthetic peptide preS(120-145). However, there is considerable amino acid variability between preS regions corresponding to distinct serological subtypes of HBV, raising the question whether the preS sequences are sufficiently related immunologically to have the potential of inducing cross-protective immunity. To answer this question concerning the preS2 region, antisera to synthetic peptides preS(120-153) and preS(128-153) corresponding to subtypes adw2 and ayw, as well as to the native env [ayw] protein were raised. Using the resulting polyclonal Ab, an immunological relatedness between preS2 sequences of subtypes adw2 and ayw was demonstrated. On the other hand, Ab selected by affinity chromatography or by cloning hybridoma cells may recognize with strong preference subtype-specific determinants within the preS2 region when the compared antigens are in solution rather than on the solid phase. These findings have implication for the design of: (1) preS2-specific immunogens and (2) immunoassays for quantitation of preS2 sequences in HBV env proteins.

Insertions in the hepatitis B surface antigen. Effect on assembly and secretion of 22-nm particles from mammalian cells

The envelope protein of hepatitis B virus carrying the surface antigen, HBsAg, has the unique property of mobilizing cellular lipids into spherical or elongated particles, about 22 nm in diameter, which are secreted from mammalian cells. We have created mutant envelope proteins by insertion of various sequences of different lengths into two regions of the S gene encoding the major envelope protein. S genes carrying inserts in phase with HBsAg were expressed in mouse L cells from the simian virus 40 early promoter. Various single or double inserts in the two major hydrophilic domains of HBsAg were compatible with secretion of 22-nm particles. In all mutant envelope proteins studied, the HBsAg domains required for intracellular aggregation appeared to be intact. However, assembly into particles was not sufficient to assure transport into the extracellular space. The 22-nm HBsAg particle may be a useful vehicle for the export and presentation of foreign peptide sequences.

Characterization of monoclonal antibodies specific for the pre-S2 region of the hepatitis B virus envelope protein

Monoclonal antibodies (McAb) specific for the pre-S region of the hepatitis B virus (HBV) envelope protein were prepared using HBV particles of hepatitis B surface antigens (HBsAg) as immunogens. The antibodies reacted in Western blot analyses and in ELISA with pre-S2 sequences of the HBV envelope protein. Pepsin or protease V8 treatment of the antigen abolished reactivity. The fine specificity of one of the McAb (F376) was established by immunoassays using synthetic peptides and a pre-S2-beta-galactosidase fusion protein expressed in E. coli. The shortest peptide recognized by F376 is demarcated by residues pre-S(132) at the N-terminal and pre-S(140)-pre-S(145) at the C-terminal. The corresponding amino acid sequence (for HBV subtype adw2) is: QDPRVRGLY(LPAGG). Additional amino acid residues at the N-terminal, and possibly at the C-terminal ends contribute to the binding of McAb, probably due to conformational influences. The McAb was applied to immunoassays of pre-S2 sequences in purified HBsAg and in human sera containing HBsAg.

Identification and chemical synthesis of a host cell receptor binding site on hepatitis B virus

Hepatitis B virus (HBV) has not yet been propagated in vitro, and knowledge concerning its reaction with receptors on target cells remained scant. We have located within the HBV envelope proteins a sequence mediating the attachment of HBV to human hepatoma HepG2 cells. A synthetic peptide analog (PLGFFPDHQLDPAFGANSNNPDWDFNP) is recognized by both cell receptors and anti-HBV antibodies and elicits antibodies reacting with native HBV. The synthetic peptide is a promising immunogen expected to elicit protective antibodies based on the concept of the attachment blockade pathway of virus neutralization. The approach described here, based on anti-peptide antisera and the binding of peptide analogs to cell receptors is generally applicable for the delineation of cell receptor binding sites on viruses with known gene sequences.

Hepatitis B virus polypeptide X: expression in Escherichia coli and identification of specific antibodies in sera from hepatitis B virus-infected humans

Sequence analysis of the hepatitis B virus (HBV) genome revealed the presence of an open reading frame (ORF X) which has the potential to encode a 154-amino acid polypeptide. A fusion protein containing 145 of the amino acids encoded by ORF X and 8 amino acids of beta-galactosidase was expressed and characterized in bacterial extracts. Immunoprecipitations with the ORF X fusion protein as a radioactively labeled antigen were performed to screen sera of humans infected with HBV for the presence of antibodies against ORF X-encoded determinants (anti-X). Such antibodies were identified in 9 samples from a set of 26 sera characterized as positive for HBV surface antigen but were not found in 16 normal human sera. The data reported here demonstrate that sera from some patients with markers of HBV infection contain antibodies directed against the polypeptide encoded by ORF X. As such, these findings represent evidence that ORF X constitutes a gene, or a portion of a gene, which is expressed during HBV infection. Although there does not appear to be a direct relationship between anti-X and any individual markers of HBV infection, our data suggest that anti-X is more prevalent in HBV-positive sera containing antibodies to HBe3 antigen (anti-HBe3).

Enhanced immunogenicity of the pre-S region of hepatitis B surface antigen

The 55 codons upstream of the gene sequence encoding the hepatitis B surface antigen (HBsAg) are called the pre-S(2) region. It has been proposed that polypeptides of high molecular weight that contain the pre-S(2) region should be included in future hepatitis B virus (HBV) vaccines. The pre-S(2) region and the S gene product [25 kilodalton (kD)] together compose a polypeptide of high molecular weight (33 kD). As an initial attempt to determine the relevance of the 33-kD polypeptide to development of an HBV vaccine, the murine immune response to pre-S(2)-encoded determinants as compared to S-encoded determinants on the same polypeptide was examined. The results indicate (i) the pre-S(2) region is significantly more immunogenic than the S region of HBsAg, (ii) the 26 amino acid residues at the NH2-terminus of the 33-kD polypeptide represent a dominant antibody binding site on the pre-S(2) region, (iii) the immune response to the pre-S(2) region is regulated by H-2-linked genes distinct from those that regulate the response to the S region, and (iv) immunization of an S region nonresponder strain with HBV envelope particles that contain both the pre-S(2) and S regions can circumvent nonresponsiveness to the S region.

The HBV HBX gene expressed in E. coli is recognised by sera from hepatitis patients

We have cloned the X gene (HBx) and the HBc antigen (HBc Ag) gene of human hepatitis B virus (HBV) in Escherichia coli as fusion products with beta-galactosidase. Both HBV genes are expressed in E. coli strain CSR 603. Expression is detected by u.v. irradiation of the bacteria, metabolic labelling and electrophoresis of the labelled extracts on SDS-polyacrylamide gels. The HBc Ag protein produced in bacteria can be recognised by anti-HBc sera and peptides derived from the protein are also recognised by anti-HBe sera. The HBx protein is recognised by some, but not all, sera which are anti-HBe positive. HBx Ag is also recognised by a woodchuck antibody similar to anti-HBe (anti-WHe). These results constitute the first proof that the open reading frame X is a true viral gene and is expressed during HBV (and WHV) infection and that an HBx/anti-HBx system, which may have important biological implications, can exist in parallel with the classic HBe/anti-HBe system.

Electron microscopic and solution X-ray scattering observations on the structure of hepatitis B surface antigen

The structure of the small, spherical hepatitis B surface antigen was studied by negative staining, freeze-fracture and freeze-etching electron microscopy and solution X-ray scattering techniques. The protein appears to be organized at the surface into a small number of morphological subunits which display two- and threefold axes of symmetry. The mean particle size was 18.3 nm by negative staining and 19.6 nm by freeze-fracture electron microscopy. The diameter of the individual subunits was about 7.5 nm with an intersubunit distance of about 10.0 nm. The lipid is distributed more homogeneously. Some heterogeneity of the particle structure is apparent which may be due to a slightly variable lipid-protein composition or incomplete or defective particle formation.

Synthetic hepatitis B surface antigen peptide vaccine

A synthetic hepatitis B surface antigen (HBsAg) peptide was prepared containing amino acid residues 122-137 of the major HBsAg polypeptide. This peptide was cyclized by the introduction of an intrachain disulfide bond between cysteine residues at positions 124 and 137 because previous studies had shown that intact disulfide bonds are critical for maintenance of HBsAg activity. An anti-HBs response was produced in mice by free peptide entrapped in liposomes. However, the immunogenicity was enhanced by aggregation into micelles, and by coupling to tetanus toxoid. Analysis of the peptide with a panel of monoclonal antibodies showed that peptide 122-137 contained a conformation (discontinuous) group a epitope and a sequential (continuous) subgroup y epitope. In addition, the cyclic peptide inhibited a human anti-HBs idiotype-anti-idiotype reaction with specificity for group a determinant(s). The potential for synthetic peptides for hepatitis B virus vaccine development is discussed.

Expression of hepatitis B virus surface antigen gene in Escherichia coli

Direct expression of hepatitis B virus (HBV) surface antigen (HBsAg) gene under the control of the Escherichia coli tryptophan operon (trp) promoter has been achieved. Synthesis of HBsAg (both complete and lacking its N-terminal segment) as a part of hybrid proteins with the N-terminal portion coded by genes cat, kan or bla is controlled by the appropriate promoters, as well as by the trp promoter. The highest levels of expression, including those for direct synthesis of HBsAg, provide the accumulation of about 10(5) polypeptide molecules per bacterial cell.

Predicted secondary structure similarity in the absence of primary amino acid sequence homology: hepatitis B virus open reading frames

Proteins that are related evolutionarily may have diverged at the level of primary amino acid sequence while maintaining similar secondary structures. Computer analysis has been used to compare the open reading frames of the hepatitis B virus to those of the woodchuck hepatitis virus at the level of amino acid sequence, and to predict the relative hydrophilic character and the secondary structure of putative polypeptides. Similarity is seen at the levels of relative hydrophilicity and secondary structure, in the absence of sequence homology. These data reinforce the proposal that these open reading frames encode viral proteins. Computer analysis of this type can be more generally used to establish structural similarities between proteins that do not share obvious sequence homology as well as to assess whether an open reading frame is fortuitous or codes for a protein.

Nucleotide sequence of a cloned duck hepatitis B virus genome: comparison with woodchuck and human hepatitis B virus sequences

The nucleotide sequence of an EcoRI duck hepatitis B virus (DHBV) clone was elucidated by using the Maxam and Gilbert method. This sequence, which is 3,021 nucleotides long, was compared with the two previously analyzed hepatitis B-like viruses (human and woodchuck). From this comparison, it was shown that DHBV is derived from an ancestor common to the two others but has a slightly different genomic organization. There was no intergenic region between genes 5 and 8, which were fused into a single open reading frame in DHBV. Genes for the surface and core proteins were assigned to open reading frames 7 and 5/8. Amino acid comparisons showed some structural relationship between gene 6 product and avian reverse transcriptase, suggesting either evolution from a common ancestor or convergence to some particular structure to fulfill a specific function. This should be correlated with the synthesis of an RNA intermediate during DNA replication. This is also taken as an argument in favor of the hypothesis that gene 6 codes for the DNA polymerase that is found within the virion. DNA sequence comparison also showed that the two mammalian hepatitis B viruses are more homologous to each other than they are to DHBV, indicating that DHBV starts to evolve on its own earlier than the two other viruses, as do birds compared with mammals. From this it is proposed that the viruses evolved in a fashion parallel to the species they infect.

Immunochemical structure of the hepatitis B surface antigen vaccine--I. Treatment of immobilized HBsAg by dissociation agents with or without enzymatic digestion and identification of polypeptides by protein blotting

Since the immunosorbent techniques and the cycles of isopycnic and rate zonal velocity ultracentrifugations were shown to be unsuitable for the purification of hepatitis B surface antigen (HBsAg) particles from human sera because HBsAg was still largely contaminated by serum proteins, we applied a drastic dissociating treatment of HBsAg stabilized by adsorption on silica gel which appeared essential to remove extraneous components initially present in the HBsAg particles. Only albumin and sometimes IgG were recovered with the purified antigen. The polypeptide composition of our purified HBsAg preparations was analyzed by SDS-PAGE with subsequent transfer to a nitrocellulose sheet by blotting, incubation with 125I-anti-HBs and exposure to X-ray film. Samples from HBsAg-positive sera containing the hepatitis B virus e antigen (HBeAg) displayed three proteins: P 24.5 and GP 28 as major components and GP 36 as a minor component. Dimers of these polypeptides were also immunologically detected. When a supplementary step of trypsin or pepsin digestion was included in our purification procedure after adsorption to silica and acid dissociation of HBsAg, proteolytic cleavage fragments of HBsAg with mol. wts lower than 10,000 were obtained on SDS-PAGE after reduction. This finding shows that arginine and lysine residues inaccessible to tryptic digestion in the intact HBsAg lipoprotein particle were exposed to enzymatic hydrolysis by our treatment. However, HBsAg kept the antigenic and immunogenic properties of the native antigen. Therefore such a HBsAg preparation appeared as a new candidate for the vaccination against HBV and a useful material for the analysis of the HBs antigenic structure.

Detection of antibodies to herpes simplex virus with a continuous cell line expressing cloned glycoprotein D

The gene for glycoprotein D of herpes simplex virus type 1 (HSV-1) was expressed in stable mammalian cell lines. Glycoprotein D produced in these cells has a number of antigenic determinants in common with the native glycoprotein. Cell lines expressing glycoprotein D were used in an enzyme-linked immunosorbent assay to detect human antibodies to glycoprotein D. This strategy should prove useful in determining the extent to which the immune response to HSV-1 is directed toward glycoprotein D.

Direct expression of hepatitis B surface antigen gene in E. coli

A 809 bp Sau 3A - Hpa I fragment containing a complete HBsAg gene and fragments 744 bp Hinc II - Hpa I and 712 bp Xba I - Hpa I containing a truncated HBsAg gene lacking the sequence encoding the NH2-terminal hydrophobic domain were prepared from a composite plasmid pHBV933 containing the 3.2 kb Eco RI DNA fragment of the entire HBV/adw genome and inserted into an expression vector pTRP801 to give plasmids pTRP SS-6, pTRP SS-39, and pTRP SS-50, respectively. The growth of a recombinant having pTRP SS-6 was greatly inhibited and the transformant expressed a low level of HBsAg, which is reactive to human anti-HBsAg antibody. Interestingly, the growth of transformants harbouring pTRP SS-39 and pTRP SS-50 was not inhibited and these transformants expressed a considerable level of the HBsAg. Minicells harbouring pTRP SS-6, pTRP SS-39, and pTRP SS-50 formed specific polypeptides of about 24 K, 23 K, and 22 K daltons, respectively.

Expression of hepatitis B virus surface antigen in yeast

The structural gene of Hepatitis B virus surface protein (HBsAg) was introduced into a plasmid capable of autonomous replication and selection in both the yeast Saccharomyces cerevisiae and E. coli. In this plasmid transcription of the HBsAg is initiated by the 5'-flanking sequence of the yeast 3-phosphoglycerate kinase (PGK) gene and terminated by the 3'-flanking region of the yeast TRP1 gene. Yeast cells containing this plasmid produce a new major species of mRNA of 1200 nucleotides in length coding for HBsAg. Viral surface antigen is made in nonglycosylated form at a level of about 1-2 percent of total yeast protein. A small fraction of this polypeptide (2-5 percent) is found in aggregated form upon yeast cell disruption by glass beads. This material is similar in size, density, and shape to the 22nm particle, isolated from the plasma of human hepatitis carriers, and induced comparable levels of HBsAg antibodies in mice when compared with the natural particle.

The complete nucleotide sequences of the cloned hepatitis B virus DNA; subtype adr and adw

The complete nucleotide sequences of two different subtypes (adr and adw) of hepatitis B virus (HBV) DNA cloned in E. coli were determined. The sequence of the viral genome of the adr clone was 3188 nucleotides long, and that of the adw clone was 3200 nucleotides long. The adr and adw clones differed from the reported cloned ayw HBV DNA (3182 nucleotides long) in 11.2% and 10.0% of nucleotides, respectively. Heterogeneity of the HBV genome in the clones with the same subtype was observed.

Specificity of antibodies elicited by a synthetic peptide having a sequence in common with a fragment of a virus protein, the hepatitis B surface antigen

We predicted the localization of a major hepatitis B surface antigen (HBsAg) determinant within residues 135-155 [Neurath, A.R., Strick, N. & Oleszko, W.R. (1981) J. Virol. Methods 3, 115-125]. A peptide corresponding to this sequence (P135-155) was synthesized, linked to macromolecular carriers, and used to immunize rabbits. In accordance with published data on shorter peptides within the same amino acid sequence, antibodies to HBsAg were elicited. A detailed analysis of the immune response to P135-155 revealed the following: A heterogeneous population of IgG and IgM antibodies reacting with P135-155 was detected in the antisera by a variety of radioimmunoassays and enzyme-linked fluorescence immunoassays. Only a subpopulation of these antibodies reacted with HBsAg. The equilibrium constant (K) for the reaction of the antibodies with HBsAg (K = 4 X 10(5) M-1) was approximately two orders of magnitude lower than K for the reaction with P135-155 and was below K for the reaction between HBsAg and antibodies elicited by HBsAg (K greater than 10(7) M-1). Preimmunization with P135-155 did not result in an enhanced response to subsequent immunization with HBsAg. Peptides more accurately mimicking determinants on HBsAg may have to be synthesized for possible application in antiviral prophylaxis.

Circular dichroism and biochemical properties of the hepatitis B virus core antigen

The hepatitis B virus (HBV) core antigen was purified by mild procedures, including hydroxyapatite column chromatography, with care taken to avoid the degradation of the particles. Circular dichroism (CD) of the HBV core particles in saline showed low intensities of negative ellipticities in the region dominated by amide bond absorption. Acid treatment of the particles induced a remarkable change in the CD spectrum, with the appearance of a positive extremum at about 208 nm. The amino acid composition and the COOH-terminal residue of the isolated core polypeptide (Mr 21,000-21,500) were shown to be essentially the same as those of the polypeptide deduced from the nucleotide sequences which had been proposed for the HBV core antigen by other laboratories. We failed to detect any NH2-terminal dansyl-derivatives from the core polypeptide by the dansyl-Edman method. We also showed by the method of fluorescein polarization that the core polypeptide conjugated with fluorescein isothiocyanate has an affinity for serum albumin. This may indicate a state of disassembled or non-assembled core polypeptide in sera.

A glycopeptide containing 15 amino acid residues derived from hepatitis B surface antigen particles: demonstration of immunogenicity to raise anti-HBs in mice

The major polypeptides composing hepatitis B surface antigen (HBsAg) particles are P-I and P-II. P-II shares the same amino acid sequence as P-I and contains an additional carbohydrate moiety of mol. wt approximately 5000. When a purified preparation of P-II was digested with Nagarse and then with Pronase P, it gave rise to a glycopeptide containing 15 amino acid residues and the carbohydrate moiety of P-II. The N-terminal amino acid sequence of the glycopeptide was determined to be Lys-Pro-Thr-Asp-Gly-Asn-. The polysaccharide moiety contained 5 moles of N-acetylglucosamine and was connected with Asn at the sixth position from the N-terminus. When mice were immunized against this HBsAg glycopeptide, they raised humoral antibodies which bound to each of three preparations of P-I derived from HGsAg particles of subtypes adw, adr and ayw, thereby indicating that the sequence of 15 amino acids in the glycopeptide would constitute a common antigenic structure of HBsAg.

Evolutionary selection for perfect hairpin structures in viral DNAs

Several recent discoveries have pointed to nucleic acid secondary structure as an additional dimension in gene expression. Further evidence for the formation of hairpins in RNA is the fact that cruciforms exist in negatively supercoiled DNAs. As potential binding sites for proteins, these structures have been proposed to play a part in the regulation of various crucial reactions, such as replication, transcription, or RNA processing. As any random nucleotide sequence can self-anneal with an approximately 50% chance of forming some Watson-Crick-type base pairs, it is difficult to assess which, if any, of all possible hairpin-like secondary structures may be biologically relevant. We have computed the expected distribution of perfectly base-paired structures as a function of loop size and stem length and compared it with the distribution observed in the complete genome of eight DNA viruses from animals, plants and bacteria. We report here that hairpins having six or more consecutive base pairs in the stem are not distributed randomly long the genome, occur much more often than chance would predict, and are particularly over-represented in regions that appear to have regulatory significance. The average loop size was found to decrease with an increase in stem length. These results support our previous hypothesis that these structures are biologically relevant.