Overexpression and purification of the hepatitis B e antigen precursor

In vitro expression of precore proteins of hepatitis B virus subgenotype A1 is affected by HBcAg, and can affect HBsAg secretion

HBeAg, a non-particulate protein of hepatitis B virus (HBV), is translated from the precore/core region as a precursor, which is post-translationally modified. Subgenotype A1 of HBV, which is a risk factor for hepatocellular carcinoma (HCC), has unique molecular characteristics in the basic core promoter/precore regions. Carriers of A1 exhibit early HBeAg loss. We sought to further characterize the precore proteins of A1 in vitro. HuH-7 cells were transfected with subgenomic constructs expressing individual precore proteins. Western blot analysis using DAKO anti-core antibody showed the expected sizes and a 1 kDa larger band for P22, P20 and P17. Using confocal microscopy, a cytoplasmic accumulation of HBeAg and precursors was observed with P25-expressing plasmid, whereas P22 localized both in the cytoplasm and nucleus. P20 and P17, which lack the carboxy end of P22 showed strong nuclear accumulation, implicating a nuclear localization signal in the N-terminal 10 amino acids. G1862T, unique to subgenotype A1, is frequently found in HBV from HCC patients. P25 with G1862T showed delayed and reduced HBeAg expression/secretion. Knock-out of core in the replication competent clones led to precore protein accumulation in the cytoplasm/perinuclear region, and decreased HBeAg secretion. Knock-out of precore proteins increased HBsAg secretion but intracellular HBsAg expression was unaffected. Over-expression of precore proteins in trans led to decreased HBsAg expression and secretion. Intracellular trafficking of HBV A1 precore proteins was followed. This was unaffected by the CMV promoter and different cell types. In the viral context, precore protein expression was affected by absence of core, and affected HBsAg expression, suggesting an interrelationship between precore proteins, HBcAg and HBsAg. This modulatory role of HBeAg and its precursors may be important in viral persistence and ultimate development of HCC.

Bioinformatic Identification of Rare Codon Clusters (RCCs) in HBV Genome and Evaluation of RCCs in Proteins Structure of Hepatitis B Virus

BACKGROUND

Hepatitis B virus (HBV) as an infectious disease that has nine genotypes (A - I) and a 'putative' genotype J.

OBJECTIVES

The aim of this study was to identify the rare codon clusters (RCC) in the HBV genome and to evaluate these RCCs in the HBV proteins structure.

METHODS

For detection of protein family accession numbers (Pfam) in HBV proteins, the UniProt database and Pfam search tool were used. Protein family accession numbers is a comprehensive and accurate collection of protein domains and families. It contains annotation of each family in the form of textual descriptions, links to other resources and literature references. Genome projects have used Pfam extensively for large-scale functional annotation of genomic data; Pfam database is a large collection of protein families, each represented by multiple sequence alignments and hidden Markov models (HMMs). The Pfam search tools are databases that identify Pfam of proteins. These Pfam IDs were analyzed in Sherlocc program and the location of RCCs in HBV genome and proteins were detected and reported as translated EMBL nucleotide sequence data library (TrEMBL) entries. The TrEMBL is a computer-annotated supplement of SWISS-PROT that contains all the translations of European molecular biology laboratory (EMBL) nucleotide sequence entries not yet integrated in SWISS-PROT. Furthermore, the structures of TrEMBL entries proteins were studied in the PDB database and 3D structures of the HBV proteins and locations of RCCs were visualized and studied using Swiss PDB Viewer software®.

RESULTS

The Pfam search tool found nine protein families in three frames. Results of Pfams studies in the Sherlocc program showed that this program has not identified RCCs in the external core antigen (PF08290) and truncated HBeAg gene (PF08290) of HBV. By contrast, the RCCs were identified in gene of hepatitis core antigen (PF00906 and the residues 224 - 234 and 251 - 255), large envelope protein S (PF00695 and the residues 53-56 and 70 - 84), X protein (PF00739 and the residues 10 - 24, 29 - 83, 95 - 99. 122 - 129, 139 - 143), DNA polymerase (viral) N-terminal domain (PF00242 and the residues 59 - 62, 214 - 217, 407 - 413) and protein P (Pf00336 and the residues 225 - 228). In HBV genome, seven RCCs were identified in the gene area of hepatitis core antigen, large envelope protein S and DNA polymerase, while protein structures of TrEMBL entries sequences found in Sherlocc program outputs were not complete.

CONCLUSIONS

Based on the location of detected RCCs in the structure of HBV proteins, it was found that these RCCs may have a critical role in correct folding of HBV proteins and can be considered as drug targets. The results of this study provide new and deep perspectives about structure of HBV proteins for further researches and designing new drugs for treatment of HBV.

Elucidating the role of the HBV e antigen in manipulating the innate immune response

ABSTRACT 

HBV causes persistent infection in approximately 300 million people and is associated with up to 2 million deaths annually. While the mechanisms by which HBV establishes and maintains infection are yet to be fully elucidated, there is mounting evidence that HBV infection in humans upregulates a range of innate immune responses and HBV has in turn has evolved mechanisms to suppress these responses. One such mechanism may be the hepatitis B e antigen (HBeAg), a soluble secreted protein which is also a major driver of adaptive immune responses. In this review, we review the literature on HBeAg-mediated regulation of innate immune responses and show that this regulation may extend beyond hepatocytes to other cell types such as NK cells which play an important role in viral clearance. Although further studies using new infection models are required, taken together these findings suggest that the HBeAg is an important regulator of the host response to infection and should not be overlooked in efforts to identify novel therapeutic targets against HBV.

Bioinformatic analysis of the hepadnavirus e-antigen and its precursor identifies remarkable sequence conservation in all orthohepadnaviruses

The hepatitis B e-antigen (HBeAg) is a non-particulate secretory protein expressed by all viruses within the family Hepadnaviridae. It is not essential for viral assembly or replication but is important for establishment of persistent infection in vivo. Although the exact mechanism(s) by which the HBeAg manifests chronicity are unclear, the HBeAg elicits both humoral and cell-mediated immunity, down-regulates the innate immune response to infection, as well as functioning as a T cell tolerogen and regulating the immune response to the intracellular nucleocapsid. A bioinformatics approach was used to show that the HBeAg and precursory genetic codes share remarkable sequence conservation in all mammalian-infecting hepadnaviruses, irrespective of host, genotype, or geographic origin. Whilst much of this sequence conservation was within key immunomodulatory epitopes, highest conservation was observed at the unique HBeAg N-terminus, suggesting this sequence in particular may play an important role in HBeAg function.

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.

Ribosome can resume the translation in both +1 or -1 frames after encountering an AGA cluster in Escherichia coli

In Escherichia coli the rare codons AGG, AGA and CGA are reported to have a detrimental effect on protein synthesis, especially during the expression of heterologous proteins. In the present work, we have studied the impact of successive clusters of these rare codons on the accuracy of mRNA translation in E. coli. For this purpose, we have analyzed the expression of an mRNA which contains in its 3' region a triplet and a tandem of AGA codons. This mRNA is derived from the human hepatitis B virus (HBV) preC gene. Both in eukaryotic cells and in eukaryotic cell-free translation system, this mRNA, directs the synthesis of a single 25 kDa protein. However, in a conventional E. coli strain BL 21 (DE3), transformed with a plasmid expressing this protein the synthesis of four polypeptides ranging from 30 to 21.5 kDa can be observed. Using different approaches, notably expression of i) precore mutated proteins or ii) chimeric proteins containing HA- and Myc-tags downstream of the AGA clusters (respectively in the -1 or +1 frame), we have found that when the ribosome encounters the AGA clusters, it can then resume the translation in both +1 and -1 frames. This result is in agreement with the model proposed recently by Baranov et al. (Baranov, P.V., Gesteland, R.F., Atkins, J.F., 2004. P-site tRNA is a crucial initiator of ribosomal frameshifting. RNA 10, 221-230), thus confirming that AGA/AGG codons can serve as sites for -1 frameshifting events. Only +1 frameshifting was suggested previously to occur at the AGA/AGG clusters.

Inhibition of translation by consecutive rare leucine codons in E. coli: absence of effect of varying mRNA stability

Consecutive homologous codons that are rarely used in E. coli are known to inhibit translation to varying degrees. As few as two consecutive rare arginine codons exhibit a profound inhibition of translation when they are located in the 5' portion of a gene in E. coli. We have previously shown that nine consecutive rare CUA leucine codons cause almost complete inhibition of translation when they are placed after the 13th codon of a test message (although they do not inhibit translation when they are placed in the middle of the message). In the present work, we report that five consecutive rare CUA leucine codons exhibit approximately a threefold inhibition of translation when they are similarly placed after the 13th codon of a test message, compared to five consecutive common CUG leucine codons, in a T7 RNA polymerase-driven system. Further, by removing RNase III processing sites at the 3' ends of the mRNAs, we have manipulated the stability of the mRNAs encoding the test and control messages to see if decreasing mRNA stability might have an effect on the extent of translation inhibition by the rare leucine codons. However, the inhibition with the less stable mRNAs was similar to that with the stable mRNAs, approximately 3.4-fold, indicating that mRNA stability per se does not have a major influence on the effects of rare codons in this system.

Construction of a cloning system for the mass production of a virus-binding protein specific for poliovirus type 1

In our previous study, virus-binding proteins (VBPs) demonstrating the ability to strongly bind poliovirus type 1 (PV1) were recovered from a bacterial culture derived from activated sludge. The isolated VBPs would be useful as viral adsorbents for water and wastewater treatments. The VBP gene of activated sludge bacteria was isolated, and the cloning system of the VBP was established. The isolation of the VBP gene from DNA libraries for activated sludge bacteria was achieved with the colony hybridization technique. The sequence of the VBP gene consisted of 807 nucleotides encoding 268 amino acids. Fifteen amino acid sequences were retrieved from 2,137,877 sequences by a homology search using the BLAST server at the National Center for Biotechnology Information. The protein encoded in the isolated genome was considered to be a newly discovered protein from activated sludge culture, because any sequences in protein databases were not perfectly matched with the sequence of the VBP. It was confirmed that Escherichia coli BL21 transformed by pRSET carrying the isolated VBP gene could extensively produce the VBP clones. Enzyme-linked immunosorbent assay (ELISA) revealed that the VBP clone exhibited the binding ability with intact particles of PV1. The equilibrium binding constant between PV1 and VBP in the ELISA well was estimated to be 2.1 x 10(7) (M(-1)), which also indicated that the VBP clones have a high affinity with the PV1 particle. The VBP cloning system developed in this study would make it possible to produce a mass volume of VBPs and to utilize them as a new material of the specific adsorbent in several technologies, including virus removal, concentration, and detection.

Critical overview and outlook: pathogenesis, prevention, and treatment of hepatitis and hepatocarcinoma caused by hepatitis B virus

Viral hepatitis B is an enigmatic disease in which the host's own immune response to persistent viral infection may bring about host destruction through antiviral inflammatory responses which might otherwise present as a benign or inapparent disease. The simple solution to the hepatitis B problem is by immunoprophylaxis using the vaccine licensed in 1981, which prevents both infection and the late sequelae of liver cirrhosis and hepatocarcinoma. Immunotherapeutic vaccines against persistent hepatitis B infection have not been successful and new explorations are being directed to therapies which include antisense, ribozymes, gene silencing by RNA interference (RNAi) and aptamer approaches. Limited benefits from nucleoside therapy and limitations in opportunity for liver transplantation have left a large void of curative treatments. Findings with respect to e antigen tolerance provide a basis for exploration to determine whether passively administered e antigen might suppress cell-mediated immunity, creating a commensal state in which virus persists but without pathologic damage to the host. Therapy of hepatocarcinoma by conventional chemotherapy, radiation, or surgical resection and ablation gives little hope for restoration of health unless the tumor is detected very early. The large engagement of the world medical science community to develop therapeutic vaccines against cancer is now in major clinical trials to determine the hope and credibility for the immunization approach. Vaccines based on tumor peptides which are linked to heat shock proteins and directed to host dendritic cells give reason for excitement and may be the "best show in town". A new era of tumor therapy will need to be based on new discoveries in immune function which are required to pursue immunotherapy on a more rational basis. The many facets of current hepatitis B virology, pathogenesis, immunoprophylaxis, immunotherapeusis, chemotherapy, and tumor pathogenesis and therapy are discussed here, in depth, but in keeping with needed brevity.

Lactic acid bacteria as prime candidates for codon optimization

In species having a strong correlation of expressivity and codon bias it has been shown that heterologous expression can be optimized by changing codons of the introduced gene towards the set of codons that the host organism naturally uses in its highly expressed genes. Even though two lactic acid bacteria are fully sequenced, there are no reports on attempts of codon optimization in the literature. In this report it is demonstrated that codons used in highly expressed genes tend to differ from the codons in lowly expressed genes, and that there is a strong correlation of codon bias and empirical expressivity (codon adaptation index) in Lactococcus lactis and Lactobacillus plantarum. This strongly suggests that codon optimization strategies could be applied to expression systems with lactic acid bacteria as producer strains. A good example of a candidate for codon optimization is the mouse interleukin-2 gene, which in its natural form has an extremely low codon adaptation index for expression in Lc. lactis.

In vitro and in vivo interactions between the hepatitis B virus protein P22 and the cellular protein gC1qR

gC1qR, a mitochondrial matrix protein, was identified as the main cellular partner of the hepatitis B virus P22 protein. We demonstrated by immunofluorescence studies that some P22 molecules were colocalized with the endogenous gC1qR in both the cytoplasm and the nucleus but never in the mitochondria. We also showed that the last 34 amino acids of P22 were involved in the association with gC1qR.