Evaluation of hepatitis C virus envelope proteins expressed in E. coli and insect cells for use as tools for antibody screening

High-yield production of a chimeric glycoprotein based on permuted E1 and E2 HCV envelope ectodomains

In this report it is described for the first time the expression and purification of large quantities of a soluble and correctly folded chimeric recombinant protein, E2661E1340, containing the permuted Hepatitis C virus (HCV) glycoprotein ectodomains E1 (amino acids 192-340) and E2 (amino acids 384-661). Using the baculovirus/insect cell expression system, 8mg of secreted protein were purified from 1L of culture media, a yield 4 times higher than the described for its counterpart E1341E2661. This permuted chimeric protein is glycosylated and possesses a high tendency to self-associate. The fluorescence emission spectrum indicates that Trp residues occupy a relatively low hydrophobic environment. The secondary structure was determined by deconvolution of the far-UV circular dichroism spectrum yielding 13% α-helix structure, 49% extended structure and 38% non-ordered structure. E2661E1340 binds to antibodies present in human sera from HCV-positive patients, a binding that is blocked at different levels by a rabbit anti-E2661 antibody. All these structural and antigenic features of E2661E1340 are very similar to those described for E1340E2661, Thus, this high-yield isolated chimeric protein may be a valuable tool to study the first steps of the HCV infection.

Carbohydrate synthesis and biosynthesis technologies for cracking of the glycan code: recent advances

The glycan code of glycoproteins can be conceptually defined at molecular level by the sequence of well characterized glycans attached to evolutionarily predetermined amino acids along the polypeptide chain. Functional consequences of protein glycosylation are numerous, and include a hierarchy of properties from general physicochemical characteristics such as solubility, stability and protection of the polypeptide from the environment up to specific glycan interactions. Definition of the glycan code for glycoproteins has been so far hampered by the lack of chemically defined glycoprotein glycoforms that proved to be extremely difficult to purify from natural sources, and the total chemical synthesis of which has been hitherto possible only for very small molecular species. This review summarizes the recent progress in chemical and chemoenzymatic synthesis of complex glycans and their protein conjugates. Progress in our understanding of the ways in which a particular glycoprotein glycoform gives rise to a unique set of functional properties is now having far reaching implications for the biotechnology of important glycodrugs such as therapeutical monoclonal antibodies, glycoprotein hormones, carbohydrate conjugates used for vaccination and other practically important protein-carbohydrate conjugates.

Genetic analysis of the carboxy-terminal region of the hepatitis C virus core protein

Hepatitis C virus (HCV) is a liver-tropic pathogen with severe health consequences for infected individuals. Chronic HCV infection can progress to cirrhosis and hepatocellular carcinoma and is a leading indicator for liver transplantation. The HCV core protein is an essential component of the infectious virus particle, but many aspects of its role remain undefined. The C-terminal region of the core protein acts as a signal sequence for the E1 glycoprotein and undergoes dual processing events during infectious virus assembly. The exact C terminus of the mature, virion-associated core protein is not known. Here, we performed genetic analyses to map the essential determinants of the HCV core C-terminal region, as well as to define the minimal length of the protein that can function for infectious virus production in trans.

The poor contribution of chimpanzee experiments to biomedical progress

Biomedical research on captive chimpanzees incurs substantial nonhuman animal welfare, ethical, and financial costs that advocates claim resultin substantial advancements in biomedical knowledge. However, demonstrating minimal contribution toward the advancement of biomedical knowledge generally, subsequent papers did not cite 49.5% (47/95), of 95 experiments randomly selected from a population of 749 published worldwide between 1995 and 2004. Only 14.7% (14/95) were cited by 27 papers that abstracts indicated described well-developed methods for combating human diseases. However, detailed examination of these medical papers revealed that in vitrostudies, human clinical and epidemiological studies, molecular assays and methods, and genomic studies contributed most to their development. No chimpanzee study made an essential contribution, or, in most cases, a significant contribution of any kind, to the development of the medical method described. The approval of these experiments indicates a failure of the ethics committee system. The demonstrable lack of benefit of most chimpanzee experimentation and its profound animal welfare and bioethical costs indicate that a ban is warranted in those remaining countries - notably the United States - that continue to conduct it.

Effect of the 5′ non-translated region on self-assembly of hepatitis C virus genotype 1a structural proteins produced in insect cells

The effect of the 5' non-translated region (5'NTR) on hepatitis C virus (HCV) morphogenesis in insect cells is investigated in this study. Expression in baculovirus-infected cells of a sequence encoding the C and E1 structural proteins under the control of the very late promoter P10 (AcSLP10-C-E1) led to the synthesis of C and C-E1 complexes, essentially found in dense reticular material associated with the ER and sedimenting at a density of 1.24-1.26 g ml(-1). Addition of the 5'NTR upstream of the C-E1 sequence (AcSLP10-5'NTR-E1) prevents translation from the initiating codon, probably because of the presence of five AUG codons in this sequence. When cells were co-infected with these two viruses, virus-like particles (VLPs) were found in the cytoplasm. The size and shape of these VLPs were variable. Concomitantly, a shift in the sedimentation profile from 1.24-1.26 to 1.15-1.18 g ml(-1) was observed, suggesting an association of C/E1 with the ER membrane. A unique vector was then constructed bearing a mutated 5'NTR (mutation of the five AUGs) and the sequence encoding all of the structural proteins and part of NS2 (5'NTRm-C-E1-E2-p7-NS2Delta). Translation of structural proteins was restored and electron microscopic observation of a cytoplasmic extract showed the presence of icosahedral particles with a density of 1.15-1.18 g ml(-1).

Hepatitis C virus infection in dialysis and chronic liver patients: Viraemia dependent anti-E2-antibody response

Cryptic hepatitis C virus (HCV) infection relates to patients infected chronically with HCV that are seronegative but have HCV-RNA. These patients are not identified by the standard serological tests for HCV, which are based on detection of antibodies to core, NS3 and NS5 antigens. They will, therefore, be wrongly diagnosed as non-infected, and are considered as a potential risk for others. Cryptic HCV infection in dialysis units occurs frequently and, due to medical procedures, is a major factor for contracting the virus when unrecognised. This study was conducted in order to assess the humoral immune responses to E2-antigen in sera of patients infected chronically with HCV. Recombinant E2 protein in enzyme linked immunosorbent assay (ELISA) and Western blot (WB) were used to test the occurrence of anti-E2 antibodies in the sera of patients from the liver clinic and of dialysis patients. The presence of E2 antibodies was found to be correlated with the presence of HCV-RNA and with viral load. Antibodies to the E2 protein could be detected in as many as 30% of the sera from dialysis patients with cryptic HCV infection (HCV-RNA only). The results suggest that detection of anti-E2 antibodies may enhance significantly HCV serological standard testing; especially among patients on dialysis, and that antibodies to envelope E2 protein appear to depend on and correlate with the presence of HCV particles.

High-level expression of the C-terminal hydrophobic region of HCV E2 protein ectodomain in E. coli

High-level expression of hepatitis C virus (HCV) E2 protein fragments encompassing its C-terminal hydrophobic region (downstream of aa 661) in Escherichia coli has been proven difficult. The extreme hydrophobicity of this region has been suspected to be detrimental to the host. In this work, we found that the C-terminal region (downstream of aa 565) of E2 ectodomain interfered with full-length expression of E2 fragments in E. coli. Nonetheless, when the central region (aa 484-622) of E2 was deleted, full-length protein was efficiently produced. C-terminal region aa 567-700 could not be efficiently expressed individually or as mouse dihydrofolate reductase (DHFR) fusion protein. However, a mutant that emerged in the cloning process was able to express full-length DHFR fusion protein. Sequencing analysis reveals the mutation to be a short frame-shift around the fusion junction, altering aa 568-571 of E2. C-terminal region of E2 ectodomain (aa 567-730) carrying this mutation was successfully expressed as hexa-histidine-tagged protein to a high level. The protein was highly insoluble and was purified under denaturing conditions. The purified protein displayed HCV E2-specific antigenicity in Western blot and specific rabbit antiserum was raised against it. These results demonstrate that hydrophobicity of the C-terminal region of E2 ectodomain is not harmful to E. coli host and has no dominative adverse effect on its bacterial expression. Other nucleotide and/or amino acid sequence properties seem to play a more important role. This finding opens up new possibilities for the development of novel bacterially-derived E2 proteins for research and clinical applications.

Characterization of secreted and intracellular forms of a truncated hepatitis C virus E2 protein expressed by a recombinant herpes simplex virus

A replication-defective herpes simplex virus type 1 (HSV-1) recombinant lacking the glycoprotein H (gH)-encoding gene and expressing a truncated form of the hepatitis C (HCV) E2 glycoprotein (E2-661) was constructed and characterized. We show here that cells infected with the HSV/HCV recombinant virus efficiently express the HCV E2-661 protein. Most importantly, cellular and secreted E2-661 protein were both readily detected by the E2-conformational mAb H53 and despite the high expression levels, only limited amounts of misfolded aggregates were detected in either the cellular or secreted fractions. Furthermore, cell-associated and secreted E2-661 protein bound to the major extracellular loop (MEL) of CD81 in a concentration-dependent manner and both were highly reactive with sera from HCV-infected patients. Finally, BALB/c mice immunized intraperitoneally with the recombinant HSV/HCV virus induced high levels of anti-E2 antibodies. Analysis of the induced immunoglobulin G (IgG) isotypes showed high levels of IgG2a while the levels of the IgG1 isotype were significantly lower, suggesting a Th1-type of response. We conclude that the HSV-1 recombinant virus represents a promising tool for production of non-aggregated, immunologically active forms of the E2-661 protein and might have potential applications in vaccine development.

Immunological evaluation of Escherichia coli-derived hepatitis C virus second envelope protein (E2) variants

Two variants of the hepatitis C virus (HCV) E2 envelope protein, lacking the C-terminal domain and comprising amino acids 458-650 (E2A) and 382-605 (E2C), respectively, were efficiently produced in BL21 (DE3) Escherichia coli cells. E2A and E2C were used to immunize mice. The E2C variant induced the maximal mean antibody titer. Anti-E2C mouse sera reacted mainly with E2 synthetic peptides covering the 70 amino acid N-terminal region of the E2 protein. Moreover, a panel of anti-HCV positive human sera recognized only the E2C protein (28.2%) and the synthetic peptide covering the HVR-1 of the E2 protein (23.1%). These data indicate the existence of an immunologically relevant region in the HVR-1 of the HCV E2 protein.

The transmembrane domain of the hepatitis C virus E2 glycoprotein is required for correct folding of the E1 glycoprotein and native complex formation

Hepatitis C virus (HCV) encodes two glycoproteins, E1 and E2, that interact to form both native and aggregated complexes in tissue culture cells. In native complexes, E1 and E2 are associated by noncovalent interactions and such complexes are considered to constitute the authentic interactions between the proteins. By contrast, the proteins are linked by covalent, disulfide bonds in aggregated complexes. From studies with a mutant in which cysteine residues in E1 have been substituted with other amino acids, we show that E1 continues to associate with E2, although the migratory patterns of the proteins on gels are consistent with the formation of aggregated complexes. Therefore, such complexes can be stabilized by noncovalent as well as covalent interactions. To further examine the requirements for native complex formation, segments of foreign glycoproteins were linked to regions of E2. Our data provide direct evidence for the requirement of C-terminal sequences in E2 that contain the transmembrane domain to permit oxidation of E1 and assembly of a native complex. By contrast, native complexes and oxidized E1 are not found in the presence of chimeric proteins containing the E2 ectodomain. These data suggest that interaction of E1 with the E2 transmembrane domain is critical for native complex formation.

Viral persistence, antibody to E1 and E2, and hypervariable region 1 sequence stability in hepatitis C virus-inoculated chimpanzees

The relationship of viral persistence, the immune response to hepatitis C virus (HCV) envelope proteins, and envelope sequence variability was examined in chimpanzees. Antibody reactivity to the HCV envelope proteins E1 or E2 was detected by enzyme-linked immunosorbent assay (ELISA) in more than 90% of a human serum panel. Although the ELISAs appeared to be sensitive indicators of HCV infection in human serum panels, the results of a cross-sectional study revealed that a low percentage of HCV-inoculated chimpanzees had detectable antibody to E1 (22%) and E2 (15%). Viral clearance, which was recognized in 28 (61%) of the chimpanzees, was not associated with an antibody response to E1 or E2. On the contrary, antibody to E2 was observed only in viremic chimpanzees. A longitudinal study of animals that cleared the viral infection or became chronically infected confirmed the low level of antibody to E1, E2, and the HVR-1. In 10 chronically infected animals, the sequence variation in the E2 hypervariable region (HVR-1) was minimal and did not coincide with antibody to E2 or to the HVR-1. In addition, low nucleotide and amino acid sequence variation was observed in the E1 and E2 regions from two chronically infected chimpanzees. These results suggest that mechanisms in addition to the emergence of HVR-1 antibody escape variants are involved in maintaining viral persistence. The significance of antibodies to E1 and E2 in the chimpanzee animal model is discussed.

Hepatitis C virus E1 protein induces modification of membrane permeability in E. coli cells

The E1 gene of hepatitis C virus (HCV) has been cloned and expressed in BL21(DE3)pLys Escherichia coli strain by pET3a vector to analyze changes in membrane permeability produced by this protein. We showed that the expression of E1 (aa 192-383), as well as of two C-terminal fragments (aa 331-383 and aa 341-383) corresponding to the transmembrane (TM) region of this protein, induced a rapid lysis of cells. On the contrary, the expression of a mutant of E1 (aa 192-340), lacking the last 40 amino acids, did not cause cell lysis. The analysis of permeability changes revealed that modification of membrane permeability to several compounds were observed only in clones expressing E1 and C-terminal fragments, while the synthesis of the C-terminal-deleted mutant had little or no effect on permeability. These findings demonstrate that the TM domain of E1 protein has membrane-active properties that may be involved in some aspects of virus-cell interaction.