High efficiency prokaryotic expression and purification of a portion of the hepatitis C core protein and analysis of the immune response to recombinant protein in BALB/c mice

Expression and Purification of HCV Core and Core-E1E2 Proteins in Different Bacterial Strains

BACKGROUND

Hepatitis C virus (HCV) is a main public health problem causing chronic liver infection and subsequently liver cirrhosis and lethal hepatocellular carcinoma (HCC). Vaccination based on HCV capsid proteins has attracted a special interest for prevention of viral infections. The core protein is a basic and evolutionary most conserved protein, which regulates the cellular processes related to viral replication and pathogenesis. The envelope E1 and E2 proteins involve in generation of the infectious particles, viral entry by binding to a host cell receptor, and modulation of the immune responses.

OBJECTIVES

In current study, the efficient generation of recombinant core and core-E1E2 proteins was developed in bacterial expression systems.

MATERIALS AND METHODS

The expression of HCV core and core-E1E2 proteins was performed using prokaryotic pET-28a and pQE-30 expression systems in BL21/ Rosetta, and M15 strains, respectively. The recombinant proteins were purified using affinity chromatography under native conditions and also reverse staining method. Finally, the levels of recombinant proteins were assessed by BCA kit and spectrophotometer.

RESULTS

The data showed a clear band of ~573 bp for HCV core and ~2238 bp for core-E1E2 genes in agarose gel. Moreover, a ~21 kDa band of core protein and a ~83 kDa band of core-E1E2 protein were revealed in SDS-PAGE. The affinity chromatography could not purify the core and core-E1E2 proteins completely, because of low affinity to Ni-NTA bead in comparison with reverse staining method.

CONCLUSIONS

This study is the first report for purification of HCV core and core-E1E2 proteins using the reverse staining procedure with no need of any chromatography columns. The BL21 strain was more potent than Rosetta strain for HCV core protein in pET 28a expression system. Furthermore, M15 strain was suitable for expression of coreE1E2 in pQE-30 bacterial system.

Hepatitis C virus core protein is a dimeric alpha-helical protein exhibiting membrane protein features

The building block of hepatitis C virus (HCV) nucleocapsid, the core protein, together with viral RNA, is composed of different domains involved in RNA binding and homo-oligomerization. The HCV core protein 1-169 (C(HCV)169) and its N-terminal region from positions 1 to 117 (C(HCV)117) were expressed in Escherichia coli and purified to homogeneity suitable for biochemical and biophysical characterizations. The overall conformation and the oligomeric properties of the resulting proteins C(HCV)169 and C(HCV)117 were investigated by using analytical centrifugation, circular dichroism, intrinsic fluorescence measurements, and limited proteolysis. Altogether, our results show that core protein (C(HCV)169) behaves as a membranous protein and forms heterogeneous soluble micelle-like aggregates of high molecular weight in the absence of detergent. In contrast, it behaves, in the presence of mild detergent, as a soluble, well-folded, noncovalent dimer. Similar to findings observed for core proteins of HCV-related flaviviruses, the HCV core protein is essentially composed of alpha-helices (50%). In contrast, C(HCV)117 is soluble and monodispersed in the absence of detergent but is unfolded. It appears that the folding of the highly basic domain from positions 2 to 117 (2-117 domain) depends on the presence of the 117-169 hydrophobic domain, which contains the structural determinants ensuring the binding of core with cellular membranes. Finally, our findings provide valuable information for further investigations on isolated core protein, as well as for attempts to reconstitute nucleocapsid particles in vitro.

Western blot screening for monoclonal antibodies against human separase

Separase is a cysteine protease that participates in separation of sister chromatids during mitosis. Human separase is a 230-kDa enzyme that is inhibited by binding to its protein inhibitor securin, specific phosphorylation, and subcellular localization. To further characterize human separase, we raised monoclonal antibodies specific against a C-terminal fragment of the protein. A critical step in monoclonal antibody production procedure is the primary screening of hybridoma supernatants. Here we report primary screening protocol utilizing Western blot analysis. The described screening protocol is carried out using fusion of a human separase fragment with two different purification tags, maltose-binding protein (MBP) and glutathione S-transferase (GST). Immunization by MBP-fusion was followed by primary screening with both MBP- and GST-separase fusions combined in the same preparation separated in SDS-PAGE. This highly sensitive screening approach reduced the number of positive signals by eliminating antibodies specific for the purification tag used in the immunization procedure. The described separase-specific antibodies were suitable for detection of endogenous separase in crude extracts, immunoprecipitation, and immunofluorescent cell staining experiments. The presented procedure is fast, reproducible and could be adopted as a primary screening scheme for a variety of protein antigens.

In vitro studies of core peptide-bearing immunopotentiating reconstituted influenza virosomes as a non-live prototype vaccine against hepatitis C virus

Evidence from both animal and human viral diseases indicate that cytotoxic T lymphocytes (CTL) are crucial in antiviral defense. However, a major problem to generate cytotoxic immunity is that in vivo exogenous antigens are usually presented via MHC class II pathway and normally fail to induce CTL. The aim of this study is to describe a novel non-live prototype vaccine based on immunopotentiating reconstituted influenza virosomes (IRIV) as vehicles to deliver HLA-A*0201-restricted hepatitis C virus (HCV) peptides (core 35-44 and 131-140) into the cytoplasm of at least three different target cell types [including T2, a transporter associated with antigen processing (TAP)-deficient cell line] resulting in MHC class I peptide presentation and lysis by peptide-specific CTL lines. Comparison of kinetics and analysis of the influence of peptide-stripping and Brefeldin A (BFA) reveal that there exists an endogenous, TAP-independent and BFA-sensitive pathway for virosomally delivered peptides. Moreover, virosomes containing influenza matrix peptide 58-66 can efficiently re-stimulate in vivo primed CTL and, importantly, IRIV containing HCV core peptides can even prime CTL from peripheral blood mononuclear cells of HCV(-) healthy blood donors in vitro. The fact that in vitro primed CTL are also able to specifically lyse target cells infected with recombinant vaccinia virus encoding the HCV core protein is of great importance for future studies based on in vivo mouse models. One of the most evident advantages of the virosomes in vivo will be their capability to protect the incorporated peptide from a large variety of degrading proteases.

An alternative for purification of low soluble recombinant hepatitis C virus core protein: preparative two-dimensional electrophoresis

For isolation of low soluble recombinant full-length (amino acids 1-191) core protein of hepatitis C virus (HCV) overexpressed in Escherichia coli, the advantage of combining two electrophoretic techniques, in comparison with chromatographic separation, is demonstrated. The protein extract was first solubilized in agents compatible with electrophoretic separation. Using preparative liquid phase isoelectric focusing (IEF) the protein of interest was first concentrated within a defined acidic pH range. These fractions were then submitted to preparative sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) to isolate the 22 kDa protein. The second-dimensional step allowed the isolation of 2 mg of the purified recombinant HCV core protein (rHCV-C191) from 1.5 g bacterial pellet. This quantity is sufficient to characterize the protein and to perform immunogenicity studies. This procedure of two-dimensional preparative electrophoresis is applicable to a wide range of biological samples and represents an alternative for purification of insoluble proteins.

Hepatitis C virus core protein represses p21WAF1/Cip1/Sid1 promoter activity

Hepatitis C virus (HCV) often causes a prolonged and persistent infection, and an association between hepatocellular carcinoma (HCC) and HCV infection has been noted. Recent experimental evidence using a cloned genomic region suggests that the putative core protein of HCV has numerous biological properties and is implicated as a viral factor for HCV mediated pathogenesis. WAF1/Cip1/Sid1 (p21) is the prototype of a family of proteins that inhibit cyclin-dependent kinases (CDK) and regulate cell cycle progression in eukaryotic cells. In this study, we have observed that the HCV core protein represses the transcriptional activity of the p21 promoter when tested separately by an in-vitro transient expression assay using murine fibroblasts (NIH3T3), human hepatocellular carcinoma (HepG2), and human cervical carcinoma (HeLa) cells. A deletion analysis of the p21 promoter suggested that the HCV core responsive region is located downstream of the p53 binding site. A gel mobility shift analysis showed that the HCV core protein does not bind directly to p21 regulatory sequences. Thus, the HCV core protein appears to act as an effector in the promotion of cell growth by repressing p21 transcription through unknown cellular factor(s).