Efficient expression, purification and characterization of hepatitis B virus preS1 protein from Escherichia coli

Enhanced humanization and affinity maturation of neutralizing anti-hepatitis B virus preS1 antibody based on antigen-antibody complex structure

To improve a previously constructed broadly neutralizing hepatitis B virus (HBV)-specific preS1 humanized antibody (HzKR127), we further humanized it through specificity-determining residue (SDR) grafting. Moreover, we improved affinity by mutating two residues in heavy-chain complementarity-determining regions (CDR), on the basis of the crystal structure of the antigen-antibody complex. HzKR127-3.2 exhibited 2.5-fold higher affinity and enhanced virus-neutralizing activity compared to the original KR127 antibody and showed less immunogenic potential than HzKR127. Enhanced virus-neutralizing activity was achieved by the increased association rate, providing insights into engineering potent antibody therapeutics for HBV immunoprophylaxis. HzKR127-3.2 may be a good candidate for HBV immunoprophylaxis.

Expression and purification of the synthetic preS1 gene of Hepatitis B Virus with preferred Escherichia coli codon preference

To produce high levels of hepatitis B virus (HBV) preS1 protein at low cost, a DNA fragment encoding the preS1 region, residues 1-119, of HBV adr subtype was synthesized by overlapping-PCR according to Escherichia coli (E. coli) B preferred codon usage. The synthetic preS1 gene (spreS1) was cloned into the bacterial expression vector pET-30a and transferred into the expression strain E. coli BL21(DE3). Recombinant preS1 protein with an N-terminal His6 tag was expressed at high levels in soluble form, yielding about 44% of the total cellular protein. This technique overcomes problems that existed in previously reported expression systems of preS1 or its epitope, i.e., low-level expression or expression in inclusion bodies. Using this His-tagged preS1 expression system, recombinant protein was purified by single-step affinity chromatography on a Ni-NTA column resulting in a yield was about 28 mg recombinant protein per liter culture. Furthermore, Western blotting and indirect ELISA analysis demonstrate that the reactivity of preS1-specific antibody is comparable between the recombinant and commercialized preS1 protein. Thus, our improved expression system could be used for practical, low-cost large-scale production of recombinant preS1 without refolding steps.

In vivo neutralization of hepatitis B virus infection by an anti-preS1 humanized antibody in chimpanzees

Previously, we generated a murine monoclonal antibody (mAb), KR127, that recognizes amino acids (aa) 37-45 of the preS1 of hepatitis B virus (HBV). In this study, we have constructed a humanized version of KR127 and evaluated its HBV-neutralizing activity in chimpanzees. A study chimpanzee was given a single intravenous dose of the humanized antibody, followed by intravenous challenge with adr subtype of wild type HBV, while a control chimpanzee was only challenged with the virus. The result showed that the study chimpanzee did not develop HBV infection during 1 year, while the control chimpanzee was infected, indicating that the humanized antibody exhibited in vivo virus-neutralizing activity and thus protected the chimpanzee from HBV infection. In addition, the humanized antibody bound to the preS1 of all subtypes of HBV. We first demonstrate that an anti-preS1 mAb can neutralize HBV infection in vivo. This humanized antibody will be useful for the immunoprophylaxis of HBV infection.

A new epitope tag from hepatitis B virus preS1 for immunodetection, localization and affinity purification of recombinant proteins

Previously, a murine monoclonal antibody (mAb) KR127 (IgG2a/kappa) that binds specifically to the preS1 of hepatitis B virus (HBV) was generated and the fine epitope was mapped to amino acids (aa) 37-45 (NSNNPDWDF). In this current study, the epitope in combination with KR127 was tested for protein tagging. Initially, to evaluate the importance of each residue of the KR127 epitope in antibody binding, alanine substitution mutants of the epitope were constructed and characterized for KR127 binding by immunoblot analysis and competition ELISA. The results showed that substitution of Ser(38) by alanine (S38A) increased the affinity to KR127. The mutated epitope (NANNPDWDF), designated S1 tag, was fused to the amino (N)- or carboxyl (C)-terminus of three human recombinant proteins, soluble B lymphocyte stimulator (sBLyS), the N-terminal domain of thrombopoietin (nTPO), and a mitochondrial ribosomal protein (CGI-113) for expression in mammalian cells, while it was fused to the N- or C-terminus of two proteins, a single-chain antibody fragment (ScFv) and the carboxyl-terminal domain (PAc) of the protective antigen of Bacillus anthracis for expression in Escherichia coli. The immunodetection, immunoprecipitation, and affinity purification of the expressed S1-tagged proteins by KR127 were successfully demonstrated. In addition, a KR127 mutant (AP2) with higher affinity, K(d) (0.9 nM), for the S1 tag compared to that (20 nM) of KR127 was obtained by mutational analysis of the heavy chain CDR3 (HCDR3) of KR127. The AP2 antibody was 4-fold more sensitive in detecting the S1-tagged protein than KR127. The S1 tag-KR127 or AP2 combination could be universally used for monitoring protein expression, localizing proteins, and protein purification, as well as studying protein interactions.

Purification and structural analysis of the hepatitis B virus preS1 expressed from Escherichia coli

The preS1 of hepatitis B virus (HBV) is located at the outermost part of the envelope protein and possesses several functionally important regions such as hepatocyte receptor-binding site and virus-neutralizing epitopes. As the first step to understand the structure-function relationship for the preS1 antigen, we have purified the preS1 and performed its structural characterization by circular dichroism (CD) spectroscopy. The preS1 was purified to near homogeneity from bacterially expressed glutathione S-transferase (GST)-preS1 fusion protein by two-step purification, affinity chromatography on glutathione-agarose column, and cation-exchange chromatography on Mono S column. The CD analysis showed that the purified preS1, which was largely unstructured in aqueous solution, acquired a significant (16%) alpha-helical structure when analyzed in 50% trifluoroethanol or 20 mM SDS. The results suggest that the preS1 assumes a mainly unstructured conformation and may form induced secondary structures upon binding to target proteins or under hydrophobic environment.

Fine mapping of virus-neutralizing epitopes on hepatitis B virus PreS1

We identified the epitopes on the preS1 which induce antibodies that neutralize both ad and ay subtypes of hepatitis B virus (HBV). Previously we generated murine monoclonal antibodies KR359 and KR127 that bind specifically to the preS1 of HBV. In this study we have performed fine mappings of the epitopes of the antibodies by examining their reactivity with GST fusion proteins, which contain a series of deletion mutants of the preS1. KR359 and KR127 specifically recognize aa 19-26 and 37-45 of the preS1, respectively. The antibodies neutralized both adr and ayw subtypes of the virus in an in vitro neutralization assay using in vitro infection of adult human hepatocyte primary culture by HBV. The epitopes showed little sequence divergence and the antibodies bound to the preS1 of all the HBV subtypes and variants tested.

Mouse monoclonal antibodies to hepatitis B virus preS1 produced after immunization with recombinant preS1 peptide

We have efficiently generated mouse monoclonal antibodies (MAbs), which bind specifically to amino acids 21-47 of the preS1 domain of hepatitis B virus (HBV) by immunizing mice with the preS1 peptide (amino acids, aa 1-56) conjugated to keyhole limpet hemocyanin. Hybridomas were screened by an indirect enzyme-linked immunosorbent assay (ELISA) using the purified preS1 peptide as a coated antigen. Eighteen positive hybridomas were selected and subjected to isotyping. Of these, 5 clones secreted immunoglobulin G (IgG) and 13 clones secreted IgM. Four (KR1, KR2, KR3, and KR4) of the 5 IgG MAbs bound to preS1 peptide (aa 21-47). Epitope mapping using bacterially expressed GST fusion proteins revealed that three clones (KR2, KR3, KR4) (IgG1, K) recognize aa 21-35, while KR1 (IgG2a, K) recognizes aa 35-47 of the preS1. These MAbs immunoprecipitated HBV particles, demonstrating that they bind to native HBV particles.

An 80-kilodalton protein that binds to the pre-S1 domain of hepatitis B virus

It has been suggested that hepatitis B virus (HBV) binds to a receptor on the plasma membrane of human hepatocytes via the pre-S1 domain of the large envelope protein as an initial step in HBV infection. However, the nature of the receptor remains controversial. In an attempt to identify a cell surface receptor for HBV, purified recombinant fusion protein of the pre-S1 domain of HBV with glutathione S-transferase (GST), expressed in Escherichia coli, was used as a ligand. The surface of human hepatocytes or HepG2 cells was biotinylated, and the cell lysate (precleared lysate) which did not bind to GST and glutathione-Sepharose beads was used as a source of receptor molecules. The precleared lysate of the biotinylated cells was incubated with the GST-pre-S1 fusion protein, and the bound proteins were visualized by Western blotting and enhanced chemiluminescence. An approximately 80-kDa protein (p80) was shown to bind specifically to the pre-S1 domain of the fusion protein. The receptor binding assay using serially or internally deleted segments of pre-S1 showed that amino acid residues 12 to 20 and 82 to 90 are essential for the binding of pre-S1 to p80. p80 also bound specifically to the pre-S1 of native HBV particles. Analysis of the tissue and species specificity of p80 expression in several available human primary cultures and cell lines of different tissue origin showed that p80 expression is not restricted to human hepatocytes. Taken together the results suggest that p80 may be a component of the viral entry machinery.

Production of hepatitis B virus preS polypeptide in Escherichia coli by mutation of the 5'-end coding sequence and its purification and characterization

The preS1 and preS2 antigens (preS Ag) of hepatitis B virus (HBV) elicit virus-neutralizing and protective antibodies which can overcome nonresponsiveness to the currently available vaccine for HBV and also carry the attachment site to HBV hepatocyte receptor. Therefore, in order to study the development of more effective vaccine and the receptor-ligand interaction, it will be helpful to obtain high-level production of the preS Ag from bacteria. We have found that the native preS region gene was not expressed under the control of commonly used promoters in Escherichia coli. By site-directed mutagenesis of some nucleotides at the 5'-end of the preS1 region gene, we have generated a mutant gene which is highly expressed in soluble form in E. coli. The produced polypeptide could be efficiently purified by 20% ammonium sulfate precipitation and a gel permeation chromatography and the purified polypeptide was demonstrated to exhibit the antigenicity and the immunogenicity of the preS1 and preS2 Ag, suggesting that it is functional.