Overexpression of HIV-1 proteins in Escherichia coli by a modified expression vector and their one-step purification

Prostate cancer biomarker annexin A3 detected in urines obtained following digital rectal examination presents antigenic variability

OBJECTIVES

Annexin A3 (ANXA3) is a potential marker for prostate cancer (PCa). We aimed to develop robust immunoassays suitable for quantifying ANXA3 in urine samples obtained following digital rectal examination (DRE) in order to facilitate the diagnostic performance evaluation of this marker.

DESIGN AND METHODS

Anti-ANXA3 monoclonal antibodies were generated and their epitopes mapped. Two different ANXA3 assay prototypes were established on the VIDAS® automated immunoanalyser and analytical validation was carried out using post-DRE urine samples obtained from patients with PCa (n=23) or benign prostate hyperplasia (n=31).

RESULTS

The assays had the same capture antibody (TGC44) but different detection antibodies (13A12 or 5C5), recognizing novel distinct epitopes. Both had a lower limit of quantification <1ng/mL and were highly specific for ANXA3, not cross-reacting with other annexins. Interassay imprecision was ≤11% and ≤15% for 13A12 and 5C5 assays, respectively. Surprisingly, a total lack of correlation was observed between ANXA3 levels measured by these two assays in post-DRE urines, indicating detection of distinct antigenic variants. Two freeze-thaw cycles did not affect analyte stability in either assay, whereas a lack of stability of antigenic variants was observed when samples were stored at -80°C for 1month.

CONCLUSIONS

Two different antigenic variants of ANXA3 are present in post-DRE urines and their clinical significance for diagnosis of prostate cancer should be further investigated. These variants are not stable over time in samples preserved at -80°C. Until this issue is resolved, ANXA3 should only be measured in freshly collected samples.

The extradomain A of fibronectin (EDA) combined with poly(I:C) enhances the immune response to HIV-1 p24 protein and the protection against recombinant Listeria monocytogenes-Gag infection in the mouse model

The development of effective vaccines against HIV-1 infection constitutes one of the major challenges in viral immunology. One of the protein candidates in vaccination against this virus is p24, since it is a conserved HIV antigen that has cytotoxic and helper T cell epitopes as well as B cell epitopes that may jointly confer enhanced protection against infection when used in immunization-challenge approaches. In this context, the adjuvant effect of EDA (used as EDAp24 fusion protein) and poly(I:C), as agonists of TLR4 and TLR3, respectively, was assessed in p24 immunizations using a recombinant Listeria monocytogenes HIV-1 Gag proteins (Lm-Gag, where p24 is the major antigen) for challenge in mice. Immunization with EDAp24 fusion protein together with poly(I:C) adjuvant induced a specific p24 IFN-γ production (Th1 profile) as well as protection against a Lm-Gag challenge, suggesting an additive or synergistic effect between both adjuvants. The combination of EDA (as a fusion protein with the antigen, which may favor antigen targeting to dendritic cells through TLR4) and poly(I:C) could thus be a good adjuvant candidate to enhance the immune response against HIV-1 proteins and its use may open new ways in vaccine investigations on this virus.

Polysaccharide-based vaccine delivery systems: Macromolecular assembly, interactions with antigen presenting cells, and in vivo immunomonitoring

Using a strategy of macromolecular assembly, a colloidal vaccine delivery system was obtained from chitosan and dextran sulfate and loaded with an antigenic protein (p24, the capsid protein of HIV-1). The colloidal polyelectrolyte complexes (PECs) were obtained by charge neutralization of the polyanion and polycation at a charge ratio (n(+)/n(-)) of 2 (CHDS). The conditions of assembly were tuned to maintain the colloidal properties of the carrier in high salt environment. The relative molar masses of the two polyions and the degree of acetylation (DA) of chitosan were essential parameters to achieve this goal, and this could be related to the nanometric scale organization of the colloids observed by Small Angle X-rays Scattering experiments. The binding of p24 to the colloidal carrier was achieved and the release of the antigen was investigated. Antigen presenting cells [dendritic cells (DCs)], obtained from monocytes, could internalize the colloids. Immature DCs (iDCs) were not matured by the colloidal PECs either loaded or not loaded with p24, as proved by Fluorescent Activated Cell Sorting (FACS) analysis. Despite this lack of in vitro interaction, a specific immune response was observed in mice with a high production of antibodies, after subcutaneous injection. The analysis of the interleukin production shows that both the cellular and the humoral responses were stimulated. This work brings a physico-chemical insight on polysaccharide-based antigen delivery systems and opens up new perspectives for their use as vaccine carriers.

Dendritic cells loaded with HIV-1 p24 proteins adsorbed on surfactant-free anionic PLA nanoparticles induce enhanced cellular immune responses against HIV-1 after vaccination

Biodegradable nanoparticles with surface adsorbed antigens represent a promising method for in vivo delivery of vaccines targeting a wide range of infectious diseases or cancers. We investigated the feasibility of loading dendritic cells with a vaccine antigen, HIV p24 protein, on the surface of surfactant-free anionic (d,l-lactic acid, PLA) nanoparticles. The p24 protein had a high affinity for the nanoparticles and the antigenicity and immunogenicity of the p24 protein on the nanoparticle was well preserved after immunization. p24-coated nanoparticles were efficiently taken up by mouse dendritic cells (DCs), inducing DC maturation by increasing MHC-I, MHC-II, CD40, CD80 and CD86 surface expression and secreting IL-12 (p70) and IL-4. We evaluated the ability of DCs pulsed with p24-coated nanoparticles to elicit an optimal humoral and cellular immune response in the blood and intestine. DCs pulsed with p24-nanoparticles induced high seric and mucosal antibody production and elicited strong systemic and local lymproliferative responses, correlated with a Th1/Th2-type response, and systemic CTL responses in mice. Thus, DCs pulsed with antigen-loaded PLA nanoparticles may provide a novel delivery tool for cell therapy vaccination against chronic infectious diseases.

Formulation of HIV-1 Tat and p24 antigens by PLA nanoparticles or MF59 impacts the breadth, but not the magnitude, of serum and faecal antibody responses in rabbits

Biodegradable nanoparticles coated with proteins represent a promising method for in vivo delivery of vaccines. Here we used a rabbit model to compare quantitatively and qualitatively the antibody responses induced by poly(D,L-lactide) nanoparticles (PLA) and by emulsion adjuvant MF59 using three HIV-1 antigens: p24gag, WT Tat and a mutated, detoxified form of Tat. We could show that all antigens and adjuvants lead to the induction of similar level of IgG titres in serum when injected subcutaneously. p24, but not Tat, could also induce faecal IgG in rabbits when formulated with PLA or MF59. The nature of the adjuvant had consequences on the spectrum of specificity induced, depending on the antigen: PLA adjuvant focussed the anti-p24 response to an immunodominant domain when compared to MF59. With wild-type Tat, no difference between adjuvants was observed in the spectrum of specificity induced. On the opposite, detoxified Tat coated on PLA increased the number of epitopes recognized by serum IgG compared to MF59 adjuvantation. The impact of these qualitative differences depending on the antigen/adjuvant associations will be important to take into account for further designs of vaccinal formulation using particulate adjuvants.

Design and characterization of an HIV-1 Tat mutant: Inactivation of viral and cellular functions but not antigenicity

Among HIV-1 proteins, Tat is a promising antigen for consideration as a component of anti-HIV-1 vaccine formulations. Nevertheless, this viral protein is able to affect the expression of several cellular genes that are implicated in immune response. In this study, we designed and characterized a mutant form of Tat ("STLA Tat"), which is unable to transactivate viral transcription, and which has lost the deleterious effects on the expression of MHC I, IL-2, and CD25 genes compared with wild-type Tat, as observed in lymphoid Jurkat cells that stably express the tat genes. In vivo experiments in mice revealed that STLA Tat induces anti-Tat antibodies at the same titers as wild-type Tat, which recognize both autologous and heterologous Tat antigens. Finally, STLA Tat did not induce the immunosuppression observed after injection of wild-type Tat. Therefore, this STLA Tat mutant appears to be a safe and promising antigen for further evaluation in anti-HIV-1 vaccine strategies.

Ty3 capsid mutations reveal early and late functions of the amino-terminal domain

The Ty3 retrotransposon assembles into 50-nm virus-like particles that occur in large intracellular clusters in the case of wild-type (wt) Ty3. Within these particles, maturation of the Gag3 and Gag3-Pol3 polyproteins by Ty3 protease produces the structural proteins capsid (CA), spacer, and nucleocapsid. Secondary and tertiary structure predictions showed that, like retroviral CA, Ty3 CA contains a large amount of helical structure arranged in amino-terminal and carboxyl-terminal bundles. Twenty-six mutants in which alanines were substituted for native residues were used to study CA subdomain functions. Transposition was measured, and particle morphogenesis and localization were characterized by analysis of protein processing, cDNA production, genomic RNA protection, and sedimentation and by fluorescence and electron microscopy. These measures defined five groups of mutants. Proteins from each group could be sedimented in a large complex. Mutations in the amino-terminal domain reduced the formation of fluorescent Ty3 protein foci. In at least one major homology region mutant, Ty3 protein concentrated in foci but no wt clusters of particles were observed. One mutation in the carboxyl-terminal domain shifted assembly from spherical particles to long filaments. Two mutants formed foci separate from P bodies, the proposed sites of assembly, and formed defective particles. P-body association was therefore found to be not necessary for assembly but correlated with the production of functional particles. One mutation in the amino terminus blocked transposition after cDNA synthesis. Our data suggest that Ty3 proteins are concentrated first, assembly associated with P bodies occurs, and particle morphogenesis concludes with a post-reverse transcription, CA-dependent step. Particle formation was generally resistant to localized substitutions, possibly indicating that multiple domains are involved.

A serological screening assay of human immunodeficiency virus type 1 antibodies based on recombinant protein p24-gp41 as a fusion protein expressed in Escherichia coli

The objective of this study was expression of a recombinant fusion protein p24-gp41 to gain a proper folding pattern of the proteins which could be recognized by specific antibodies against human immunodeficiency virus type 1 (HIV-1) for development of a reliable serodiagnostic kit. Serodiagnostic method using enzyme-linked immunosorbent assay (ELISA) with the expressed recombinant fusion protein p24-gp41 was carried out to test the sensitivity and specificity of the protein using human sera and various reference panels from Boston Biomedica Inc. (BBI). The level of the expression was determined to be 30% and the final recovery from fermentation and purification process was calculated as 80 mg/L with more than 98% purity. The developed ELISA assay was demonstrated to have 100 and 99.5% sensitivity and specificity, respectively, detecting anti-HIV-1 antibody using 900 positive and 10,000 negative human sera. The developed assay showed reliable results in comparison with other reference HIV ELISA kits using various BBI panels as well. In conclusion, the recombinant fusion protein p24-gp41 was expressed and used to develop a serodiagnostic kit for screening of the HIV-1 with high sensitivity (100%) and specificity (99.5%) which could be useful for screening large groups of blood donors.

Surfactant-free anionic PLA nanoparticles coated with HIV-1 p24 protein induced enhanced cellular and humoral immune responses in various animal models

Microparticles and nanoparticles prepared with poly(D,L-lactide-co-glycolide) (PLGA) or poly(D,L-lactide) (PLA) polymers represent a promising method for in vivo delivery of encapsulated peptide, protein or DNA antigens. However, one major issue that limits the potential of these delivery systems is the instability or the degradation of the entrapped antigen. Charged microparticles carrying surface adsorbed antigen were developed to resolve this problem and appear more suitable for vaccine applications. We describe here new anionic PLA nanoparticles obtained by the dialysis method that are absolutely surfactant-free, which makes them more appropriate for use in humans. The potency of this delivery system as a vaccine carrier was tested in various animal models using HIV-1 p24 protein. p24-coated PLA nanoparticles (p24/PLA) induced high antibody titres (>10(6)) in mice, rabbits and macaques. Moreover, p24/PLA nanoparticles elicited strong CTL responses and a Th1-biased cytokine release (IFNgamma, IL-2) in mice. p24 protein seemed to generate a more Th1-oriented response when administered coated onto the surface of PLA nanoparticles than adjuvanted with Freund's adjuvant. Most importantly, the ability of p24/PLA particles to induce Th1 responses was also confirmed in the macaque model, since high levels of IFNgamma-producing CD4+ T cells and CD8+ T cells could be detected by the ELISPOT assay. This protein delivery system confirms the potential of charged nanoparticles in the field of vaccine development.

Autoantibodies recognizing citrullinated rat filaggrin in an ELISA using citrullinated and non-citrullinated recombinant proteins as antigens are highly diagnostic for rheumatoid arthritis

The objective of the study was to determine the diagnostic value for rheumatoid arthritis (RA) of anti-filaggrin autoantibodies (autoAb) recognizing citrullinated recombinant rat filaggrin (ACRF) in community cases of very early arthritis. To evaluate the diagnostic value of ACRF, were studied sera from patients with different classified rheumatic diseases and healthy subjects (group 1, n= 422) and 314 community cases of very early arthritis (group 2) that were classified as RA (n = 176), non-RA (n = 63) and undifferentiated (n = 75) arthritides after 1 years of follow-up. ACRF were measured using a new ELISA, with results expressed as the difference between the OD value obtained on citrullinated minus that on noncitrullinated rat filaggrin (differential ACRF; dACRF). For both groups, rheumatoid factors (RF), anti-keratin autoAb (AKA) and anti-perinuclear factor (APF) were tested; for group 2, anti-CCP autoAb were also tested. Different reactivity patterns against citrullinated and noncitrullinated filaggrin were observed. Almost all sera reacting with citrullinated but not noncitrullinated filaggrin were from RA patients. Among RA and non-RA sera that recognized both forms of filaggrin, a positive result was obtained only with RA sera. For groups 1 and 2, dACRF sensitivity was 58.4% and 30.7%, and specificity for RA was 99.5% and 98.4%, respectively. In group 2, dACRF specificity for RA was better than that of RF (92.1%), APF (95.2%), AKA (96.8%) and anti-CCP (95.2%). dACRF positive predictive value was high (98.2) and close to that given by the concomitant positivity of RF and anti-CCP autoAb. Despite a high positive correlation between AKA, APF, anti-CCP and dACRF test results, they were complementary since some sera were positive for only one test. Thus, in a community setting, anti-citrullinated rat filaggrin reactivity detected by a new ELISA, whose originality is based on the difference between serum's reactivities on the citrullinated and native forms of filaggrin, had a higher diagnostic value for RA than other autoAb.

Molecular cloning, overexpression in Escherichia coli, and purification of 6×his-tagged C-terminal domain of Clostridium difficile toxins A and B

Genomic DNA from ribotype-01 and -17 Clostridium difficile strains was used for amplification of the sequences encoding the carboxy-terminal domain of toxins A (TcdA) and B (TcdB). The deduced C-terminal TcdB ribotype-01 and -17 domains share 99.5% amino acid sequence identity while TcdA ribotype-17 comprises a 607 amino acid deletion compared to TcdA-01. When compared to previously sequenced C. difficile toxins, 99.3% amino acid identity was found between TcdA-01 and TcdA from strain VPI10643 and 98.8% identity between TcdA-17 and TcdA from strain F-1470. The obtained sequences were fused in 3' to a sequence encoding a hexahistidine tag and cloned into an Escherichia coli expression vector. The recombinant proteins were expressed in E. coli and purified using single-step metal-chelate chromatography. The recombinant carboxy-terminal domain of TcdA-01 was purified from the soluble E. coli lysate fraction whereas TcdA-17 and TcdB-17 carboxy-terminal domains were purified from inclusion bodies. At least 40 mg of each protein was purified per liter of bacterial culture. The recombinant toxin domains were detected specifically by Western blot and ELISA with antibodies against native C. difficile toxins. This study demonstrated that the carboxy-terminal domains of TcdA and TcdB can be produced using an E. coli expression system and easily purified. These recombinant, stable, and non-toxic proteins provide a convenient source for use in the diagnosis of C. difficile infections, instead of native toxins, as controls and calibrators in immunoassay kits and to obtain specific monoclonal antibodies.

Vaccination with an adenoviral vector encoding hepatitis C virus (HCV) NS3 protein protects against infection with HCV-recombinant vaccinia virus

Cellular immune response plays an important role in the clearance of hepatitis C virus (HCV). Thus, development of efficient ways to induce anti-viral cellular immune responses is an important step toward prevention and/or treatment of HCV infection. With this aim, we have constructed a replication-deficient recombinant adenovirus expressing HCV NS3 protein (RAdNS3). The efficacy of RAdNS3 was tested in vivo by measuring the protection against infection with a recombinant vaccinia virus expressing HCV-polyprotein (vHCV1-3011). Immunisation with 10(9)pfu of RAdNS3 induced anti-NS3 humoral, T helper and T cytotoxic responses. We identified eight epitopes recognised by IFN-gamma producing cells, five of them exhibiting lytic activity. Moreover, we show that RAdNS3 immunised mice were protected against challenge with vHCV1-3011 and that this protection was mediated by CD8(+) cells. In conclusion, our results suggest that adenoviral vectors encoding NS3 might be useful for the induction of prophylactic and/or therapeutic anti-HCV immunity.

Versatile method for production and controlled polymer-immobilization of biologically active recombinant proteins

The immobilization of a protein by covalent attachment to a support matrix should involve only functional groups of the protein that are not essential for its biological activity. A general strategy for obtaining recombinant proteins designed for oriented covalent grafting onto copolymers was investigated. The rationale involves the definition of seven p24-derived recombinant proteins as fused to either distant or adjacent tags comprising primary amine rich tag consisting of six contiguous lysines suitable for oriented covalent immobilization and a hexa-histidine tag suitable for metal chelate affinity purification. High-level expression, efficient affinity purification, and coupling yields onto maleic anhydride-alt-methyl vinyl ether copolymers higher than 95% were obtained for all proteins. Afterwards, an investigation of the biological features of the immobilized vs. nonimmobilized protein onto the copolymer allowed us to select one bioconjugate which was used in a diagnostic context, i.e., as a capture antigen in an ELISA format test. Sera from 107 HIV-seropositive individuals at various stages of HIV infection, including two seroconversion panels and 104 healthy HIV-seronegative controls, were tested using either RH24 or RK24H-copolymer coated onto the microtiter plate. These assays showed that the use of such a protein-copolymer bioconjugate allowed detection of lower antibody titers than the RH24 protein, illustrating the potential of applications of such doubly tagged proteins. Thus, a set of expression vectors was designed containing four different combinations of hexa-lysine and hexa-histidine tags and a multiple cloning site, allowing the production of different recombinant fusion proteins suitable for biological reactivity conservation after immobilization.

Detection of antibodies to deiminated recombinant rat filaggrin by enzyme-linked immunosorbent assay: a highly effective test for the diagnosis of rheumatoid arthritis

OBJECTIVE

To assay antifilaggrin autoantibodies, we developed an enzyme-linked immunosorbent assay (ELISA) using a "citrullinated" recombinant rat filaggrin. Our objectives were to assess its value for diagnosing rheumatoid arthritis (RA) and to compare the results with those obtained using 4 other reference methods for detection of antifilaggrin autoantibodies, including the commercially available ELISA that uses a modified "citrullinated" synthetic peptide derived from the sequence of human filaggrin (CCP-ELISA).

METHODS

We analyzed 711 sera from patients with well-characterized rheumatic diseases, including 240 patients with RA. Antifilaggrin autoantibodies were detected by an ELISA using a recombinant rat filaggrin deiminated in vitro as immunosorbent (ArFA-ELISA). The results considered were the differences between the optical densities obtained on deiminated and nondeiminated proteins. Antibodies to rat esophagus epithelium were detected by indirect immunofluorescence, while antibodies to human filaggrin were detected by immunoblotting and by a recently described ELISA using a deiminated recombinant human filaggrin. Finally, CCP-ELISA was performed according to the manufacturer's recommendations.

RESULTS

At the titer thresholds allowing diagnostic specificities of 0.95, 0.985, and 0.99 to be reached, the diagnostic sensitivities of the ArFA-ELISA were 0.76, 0.67, and 0.65, respectively. At these 3 thresholds, the sensitivities were significantly higher than those of the 4 other tests. Despite incomplete overlapping of the 5 tests, the high diagnostic performance of the ArFA-ELISA allows us to propose this test to replace all the other methods for antifilaggrin autoantibody detection.

CONCLUSION

ArFA-ELISA appears to be the most efficient test among those available for the detection of antifilaggrin autoantibodies, in terms of diagnostic accuracy for RA. Its diagnostic performance in early RA and its prognostic value are currently under evaluation.

Erratum to "characterization and diagnostic potential of hepatitis B virus nucleocapsid expressed in E. coli and P. pastoris"

The hepatitis B core antigen (HBcAg) was expressed in Escherichia coli and in Pichia pastoris. A hexa-histidine tag was introduced at the C terminus of the E. coli expressed protein allowing its purification by Ni2+-chelate affinity chromatography. The P. pastoris expressed HBcAg was isolated following heat treatment. The two recombinant HBcAgs were purified further on a sucrose gradient. Mass spectrometry analysis suggested that HBcAg was N-acetylated only in P. pastoris and reaction with Ellman's reagent allowed the measurement, respectively, of 0.37 and 0.23 mole of free sulfydryl groups per mole of HBcAg monomer expressed in E. coli or P. pastoris. Electron microscopy indicated that the E. coli and the P. pastoris proteins formed capsid-like particles with, respectively, a diameter of 34 and 28 nm. Nucleic acid components were found entrapped in both particles but protected from enzymatic treatment only in the P. pastoris derived particles suggesting structural discrepancies between the two recombinant molecules. The high purity of these recombinant antigens allowed the development of a sandwich immunoassay to detect antibodies to HBcAg (anti-HBc) in human serum. The preliminary results indicate that the P. pastoris HBcAg produced intracellularly is more suitable than the renatured E. coli HBcAg for detection of anti-HBc in this diagnostic assay.

Construction and characterisation of infectious recombinant HIV-1 clones containing CTL epitopes from structural proteins in Nef

In this study the construction is described of HIV-1 molecular clones in which CTL epitopes from RT or Env late proteins were inserted into the Nef early protein. The ectopic epitopes were efficiently processed from the recombinant Nef proteins, were recognized by their cognate CTL in cytolytic assays, and did not perturb virus replication or viral protein expression in vitro. These recombinant viruses will therefore be an important tool in studying the effect of distinct epitope expression kinetics on the efficiency of CTL-mediated suppression of HIV-1 replication.

Characterization and diagnostic potential of hepatitis B virus nucleocapsid expressed in E. coli and P. pastoris

The hepatitis B core antigen (HBcAg) was expressed in Escherichia coli and in Pichia pastoris. A hexahistidine tag was introduced at the C terminus of the E. coli expressed protein allowing its purification by Ni(2+)-chelate affinity chromatography. The P. pastoris expressed HBcAg was isolated following heat treatment. The two recombinant HBcAgs were purified further on a sucrose gradient. Mass spectrometry analysis suggested that HBcAg was N-acetylated only in P. pastoris and reaction with Ellman's reagent allowed the measurement respectively, of 0.37 and 0.23 mole of free sulfydryl groups per mole of HBcAg monomer expressed in E. coli or P. pastoris. Electron microscopy indicated that the E. coli and the P. pastoris proteins formed capsid-like particles with respectively, a diameter of 34 and 28-nm. Nucleic acid components were found entrapped in both particles but protected from enzymatic treatment only in the P. pastoris derived particles suggesting structural discrepancies between the two recombinant molecules. The high purity of these recombinant antigens allowed the development of a sandwich immunoassay to detect anti-HBc antibodies in human serum. The preliminary results indicate that the P. pastoris HBcAg produced intracellularly is more suitable than the renatured E. coli HBcAg for detection of anti-HBc in this diagnostic assay.

Mechanisms leading to an oriented immobilization of recombinant proteins derived from the P24 capsid of HIV-1 onto copolymers

To investigate the mechanism leading to an oriented immobilization of recombinant proteins onto synthetic copolymers, five genetically modified HIV-1 p24 capsid proteins (RH24, RH24A4K2, RH24R6, RH24R4K2, and RH24K6) were tested for their efficiency to covalently bind to maleic anhydride-alt-methyl vinyl ether (MAMVE) and N-vinyl pyrrolidone-alt-maleic anhydride (NVPMA) copolymers. These proteins contain, at their C-termini, tags differing in cationic and/or reactive amino acids density. We demonstrated that an increase of the charge and amine density in the tag enhances the coupling yield, the most efficient tag being a six lysine one. The reactivity of the proteins depends directly on the reactivity of the tag, and this led us to conclude that the tag was the site where the covalent grafting with the polymer occurred. Thus, design of such tags provides a new efficient and versatile method allowing oriented immobilization of recombinant proteins onto copolymers.

Purification of recombinant HBc antigen expressed in Escherichia coli and Pichia pastoris: comparison of size-exclusion chromatography and ultracentrifugation

Hepatitis B virus core protein (HBc) is an important serology marker of hepatitis B infection and patient follow-up. It is an M, 21,000 protein, which has the intrinsic capacity to self-assemble as a capsid-like particle. The hepatitis B core protein has been expressed in Escherichia coli and Pichia pastoris (three different constructions) in order to select a HBc recombinant antigen suitable for serodiagnosis requirements with a cost effective downstream strategy. The expression and purification of the different forms of recombinant HBc have been described. For the last step, ultracentrifugation and size-exclusion chromatography were compared. The morphology of these capsids was observed using an electron microscope. Our data shows that HBc antigen is produced in large quantities in E. coli but some contaminants remained which were associated with the E. coli HBc protein after ultracentrifugation or size-exclusion chromatography. The ultracentrifugation enables a higher purity of HBc antigen to be obtained than size-exclusion chromatography but the latter enables a higher recovery rate. P. pastoris enables the expression and extraction of a highly purified HBc antigen suitable for diagnostic purposes.

Molecular specificities of antibodies against ovine and murine recombinant prion proteins

The prion proteins (PrP) from sheep and mouse were produced in large quantities of full-length protein in Escherichia coli after fusion with a carboxy-terminal hexahistidine sequence. Both recombinant proteins were recognized, at variable levels, in ELISA using a panel of antibodies recognizing different parts of the PrP molecules, from the octo-repeat region (79-92 human sequence), to the C terminal end of the protein. We show that these recombinant proteins enable polyclonal antisera to be produced in PrP0/0 mice, the sheep prion protein being strongly immunogenic, using either native or guanidium hydrochloride-treated recombinant protein. Sera produced against the sheep protein also reacted in Western blot with bovine, ovine, and murine PrP res, but showed higher reactivity with sheep PrP res. Interestingly, when compared to an antiserum produced against bovine 106-121 peptidic sequence (RB1), we found strikingly different ratios of the PrP res glycoforms, in both cattle with BSE and sheep with natural scrapie, but not in scrapie infected mice. Such results further demonstrate that the assessment of PrP res glycoform ratios, using different antibodies, may depend on antibodies species-specificities.

Mutual conformational adaptations in antigen and antibody upon complex formation between an Fab and HIV-1 capsid protein p24

BACKGROUND

Elucidating the structural basis of antigen-antibody recognition ideally requires a structural comparison of free and complexed components. To this end we have studied a mouse monoclonal antibody, denoted 13B5, raised against p24, the capsid protein of HIV-1. We have previously described the first crystal structure of intact p24 as visualized in the Fab13B5-p24 complex. Here we report the structure of the uncomplexed Fab13B5 at 1.8 A resolution and analyze the Fab-p24 interface and the conformational changes occurring upon complex formation.

RESULTS

Fab13B5 recognizes a nearly continuous epitope comprising a helix-turn-helix motif in the C-terminal domain of p24. Only 4 complementarity-determining regions (CDRs) are in contact with p24 with most interactions being by the heavy chain. Comparison of the free and complexed Fab reveals that structural changes upon binding are localized to a few side chains of CDR-H1 and -H2 but involve a larger, concerted displacement of CDR-H3. Antigen binding is also associated with an 8 degrees relative rotation of the heavy and light chain variable regions. In p24, small conformational changes localized to the turn between the two helices comprising the epitope result from Fab binding.

CONCLUSIONS

The relatively small area of contact between Fab13B5 and p24 may be related to the fact that the epitope is a continuous peptide rather than a more complex protein surface and correlates with a relatively low affinity of antigen and antibody. Despite this, a significant quaternary structural change occurs in the Fab upon complex formation, with additional smaller adaptations of both antigen and antibody.

Gag-derived proteins of HIV-1 isolates from Indian patients: cloning, expression, and purification of p24 of B- and C-subtypes

A simple and efficient method for hyperexpression in Escherichia coli and purification of capsid protein, p24, of human immunodeficiency virus type 1 (HIV-1) of both B- and C-subtypes is described. DNA-encoding p24 of C-subtype was cloned from C-subtype gag sequence which was obtained by PCR amplification using DNA extracted from peripheral blood mononuclear lymphocytes (PBMLs) of an HIV-1-infected patient from India. DNA-encoding p24B protein was amplified directly by two-step PCR using genomic DNA obtained from PBMLs of an HIV-infected individual. A T7 promoter-based expression system was optimized for hyperexpression of p24 in the soluble form. Both p24 (B- and C-subtype) were purified to near homogeneity using conventional chromatographic techniques. Purification of p24 (C subtype) was described for the first time with yield of 53 mg from 1 liter of culture. The yield of p24 (B-subtype) was 67 mg from 1 liter of culture, which was severalfold better than reported earlier. The immunoreactivity of both types of p24 to sera from HIV-infected individuals was comparable. This report describes a simple, highly efficient, and reproducible method for obtaining large quantities of highly pure p24 of both B- and C-subtype, which can be used for structural, biochemical, and immunological characterization and, eventually, for diagnostic and prognostic applications.

Overexpression in Escherichia coli and characterization of the chloroplast fructose-1,6-bisphosphatase from wheat

An important Calvin cycle enzyme, chloroplast fructose-1, 6-bisphosphatase (FBPase) from wheat, has been cloned and expressed up to 15% of the total cell protein using a pPLc expression vector in Escherichia coli by replacing the codons in the 5'-terminal encoding sequence with optimal and A/T-rich ones. The overexpressed wheat FBPase is soluble, fully active, and heat stable. It can be purified by chromatography in turn on DEAE-Sepharose and Sephacryl S-200, and around 15 mg of purified enzymes (>95%) is obtained from 1 liter of cultured bacteria. Its special activity is 8.8 u/mg, K(cat) is 22.9/S, K(m) is 121 microM, and V(max) is 128 micromol/min. mg. The recombinant FBPase can be activated by DTT, Na(+), or low concentrations of Li(+), Ca(2+), Zn(2+), GuHCl, and urea, while it can be inhibited by K(+) or NH(+)(4).

An envelope glycoprotein of the human endogenous retrovirus HERV-W is expressed in the human placenta and fuses cells expressing the type D mammalian retrovirus receptor

A new human endogenous retrovirus (HERV) family, termed HERV-W, was recently described (J.-L. Blond, F. Besème, L. Duret, O. Bouton, F. Bedin, H. Perron, B. Mandrand, and F. Mallet, J. Virol. 73:1175-1185, 1999). HERV-W mRNAs were found to be specifically expressed in placenta cells, and an env cDNA containing a complete open reading frame was recovered. In cell-cell fusion assays, we demonstrate here that the product of the HERV-W env gene is a highly fusogenic membrane glycoprotein. Transfection of an HERV-W Env expression vector in a panel of cell lines derived from different species resulted in formation of syncytia in primate and pig cells upon interaction with the type D mammalian retrovirus receptor. Moreover, envelope glycoproteins encoded by HERV-W were specifically detected in placenta cells, suggesting that they may play a physiological role during pregnancy and placenta formation.

Immunological characterization of the sheep prion protein expressed as fusion proteins in Escherichia coli

The prion protein (PrP) from sheep was produced in large quantities of entire protein in Escherichia coli after fusion with a carboxy-terminal hexahistidine sequence. In contrast, amino-terminal fusion with glutathione S-transferase (GST) revealed a high susceptibility toward cleavage of the protein. Both recombinant proteins were recognised, at variable levels, in Western blots using a panel of antibodies against the 40-56, 89-104, 98-113 and 112-115 sequences of the prion protein, similarly to the abnormal prion protein extracted from scrapie-infected sheep. Interestingly, monoclonal antibody 3F4 was found to react with these three proteins in Western blot.

Overexpression in Escherichia coli and characterization of the chloroplast triosephosphate isomerase from spinach

An important Calvin cycle enzyme, chloroplast triosephosphate isomerase (cpTPI) from spinach, has been cloned and expressed in up to 15% of the total cell protein using the P(L) expression vector in Escherichia coli. An even higher level expression, up to 36% of the total protein, was achieved by replacing the nucleotide sequence between the ribosomal binding site and the initial codon, ATG, with an AT-rich sequence. Computer modeling revealed that the moderate change in the standard free energy (5'-DeltaG degrees ) of mRNA secondary structure in the translation initial region might be the major factor which led to the later high-level expression. The overexpressed spinach cpTPI was soluble and fully active and was able to be purified beyond 95% purity by DEAE-Sepharose and Sephadex G-75, and around 55 mg of purified enzymes was obtained from 1 liter of cultured bacteria. With d-glyceraldehyde 3-phosphate as substrate, K(m (D-3-P)) is 0. 68 mM, V(max (G-3-P)) is 3.16 x 10(4) micromol/min. mg, and K(cat (G-3-P)) is 4.51 x 10(3)/s; with dihydroxyacetone phosphate as substrate, the corresponding values are 7.27 mM, 1.04 x 10(3) micromol/min. mg, and 1.16 x 10(2)/s, respectively.

Overexpression and purification of an immunologically reactive His-BIV capsid fusion protein

The gene of the capsid protein of bovine immunodeficiency virus (BIV) was linked to a sequence encoding for six histidines and expressed as the (His)6 p26 capsid fusion protein. The fusion protein was strongly expressed as both soluble and insoluble forms after induction by isopropylthio-beta-d-galactoside. Purification was based on interaction of the hexa-histidine polypeptide with metal ions. Expression could represent 11% of the total protein in Escherichia coli, allowing more than 20 mg of highly purified protein to be obtained per liter of bacterial culture. The (His)6 p26 capsid fusion protein purified by immobilized metal affinity chromatography reacted specifically in Western blot with sera from cattle experimentally infected by BIV, as well as with two monoclonal antibodies directed against different epitopes of the Gag protein. The ease of expression, purification, and specificity of this fusion protein should permit a thorough study of prevalence of BIV infection in large-scale serological studies of field samples.

Head-to-tail dimers and interdomain flexibility revealed by the crystal structure of HIV-1 capsid protein (p24) complexed with a monoclonal antibody Fab

The crystal structure of an intact molecule of HIV-1 capsid protein (p24) in complex with a monoclonal antibody fragment recognizing an epitope on the C-terminal domain has been determined at 3 A resolution. The helical N- and C-terminal domains of p24 are linked by an extended peptide forming a flexibly linked dumb-bell-shaped molecule 75 A in overall length. The p24 construct used is a variant with an N-terminal extension that mimics to some extent the Gag context of p24. We observed a novel head-to-tail dimer of p24 molecules which occurs through the formation of a substantial intermolecular interface between the N- and C-terminal domains. Comparison with previously observed p24 dimers shows that the same residues and secondary structural elements can partake in different interfaces revealing a remarkable stickiness and plasticity of the p24 molecule, properties which, combined with the inter-domain flexibility, are presumably important in the assembly and maturation of viral particles. Previous mutagenesis studies designed to test specific N-N and C-C homodimer interfaces do not discriminate fully against the possibility of the observed N-C interface.

Construction and expression of a modular gene encoding bacteriophage T7 RNA polymerase

A modular gene that encodes T7 RNA polymerase (T7 RNAP) and consists of cassettes delimited by unique restriction sites was constructed. The modular and wild-type genes of T7 RNAP were cloned into a vector designed to express His-tagged proteins. The modular and wild-type genes provided the same level of protein expression (i.e., T7 RNAP represented up to 30% of the total protein in Escherichia coli strain BL21). Purification of both proteins by immobilized metal ion affinity chromatography (IMAC) resulted in similar yields (700-800 microg of enzyme per 20 ml of culture) and purity (>95%) as indicated by Coomassie blue staining, Western blotting and the absence of detectable contaminating nuclease activities. Both proteins exhibited identical efficiency in transcription assays, and their specific activities (about 200 U/microg) were close to that of a commercial T7 RNAP preparation. The modular gene provides a useful tool for cassette directed mutagenesis of T7 RNAP.

Molecular characterization of HIV viruses generated after in vivo ligation

During the course of infection, human immunodeficiency virus type 1 (HIV-1) displays wide genotypic and phenotypic differences. Construction of chimeric viruses is useful to determine the genotypic basis that underlies phenotypic variations, but the procedure is time-consuming. Previously, it has been shown that co-transfection of truncated hemi-genomic HIV-1 proviral DNA can lead to generation of full-length infectious virus. In the study of HIV phenotypes, using this technique, it is important to determine whether recombination between the two hemigenomes occurs without mutations. After co-transfection, progeny recombinant viruses replicated at the same rate as the control. We purified progeny viruses from culture supernatants and determined mutations at the recombination site. It appeared that correct in vivo ligation depended on the purity of DNA and the restriction site used. It also appeared that some of the mutations observed affect replication, as progeny viruses bearing one of these mutations disappeared during in vitro cultures, whereas other mutants did not. Although this technique is widely applied to generate chimeric viruses, the results should be evaluated with care, since mutations influencing the phenotype of the progeny viruses may have been introduced.

B cell epitopes of HIV type 1 p24 capsid protein: a reassessment

The objective of the present study was to identify p24 antigenic domains recognized during natural human immunodeficiency virus type 1 (HIV-1) infection, the determination of the major epitopes of p24 having significant applications for both the improvement of diagnostic approaches and the development of vaccines. Reactivity of 20 HIV-1-infected patients and 8 HIV-1-negative patients was analyzed using an enzyme-linked immunosorbent assay (ELISA) developed with 45 overlapping synthetic pentadecapeptides, spanning amino acids 133 to 363 of HIV-1 p55gag precursor. Two peptides covering aa 178-192 and 288-302 of p55 were recognized by 40 and 45% of HIV-1 antibody-positive human samples, respectively. A peptide covering aa 272-322 of p55 was synthesized and recognized by most human sera in indirect ELISA. However, inhibition assays indicated that this sequence does not contain all of the immunodominant domains of p24 since it was not sufficient to block binding of human sera to whole p24. A three-dimensional model of p24 derived from the Mengovirus VP2 suggests that the two distant sequences recognized by human sera containing antibodies to HIV-1 could possibly be a part of a conformational epitope built up by two loops corresponding to aa 183-186 and 289-292.

Assembly and immunogenicity of chimeric Gag-Env proteins derived from the human immunodeficiency virus type 1

We evaluated the potential of the precursor Gag protein (Pr55) of the human immunodeficiency virus type 1 (HIV-1) as a carrier for the presentation of envelope epitopes. Recombinant chimeric core-envelope protein-expressing constructs were derived by deletion of regions within the gag gene, especially of regions encoding p24 capsid epitopes. Sequences encoding either the principal neutralization determinant (PND) and/or the CD4-binding domains (CD4BS) were then inserted. Deletion of residues 196-226 within the p24 capsid protein did not prevent self-assembly into virus-like particles (VLPs) whereas deletion of residues 299-328 completely abolished VLP formation. Thus the major homology region (MHR) and proximal sequences are required for capsid assembly. An immunization study in mice showed that assembled chimeric proteins elicited strong anti-Gag, weak anti-envelope, and no neutralizing humoral responses. Nonassembled chimeric proteins were poor immunogens. Mapping of Pr55 antigenic sites using sera from immunized mice and peptides overlapping the entire Gag precursor showed that p24 capsid and p17 matrix epitopes presented to the immune system differed from the mature form (p24 or p17) and the multimeric immature form (Pr55).

In vitro HIV1 infection of CD34+ progenitor-derived dendritic/Langerhans cells at different stages of their differentiation in the presence of GM-CSF/TNF alpha

Langerhans cells (LC) are antigen-presenting cells which are found in areas at risk of inoculation by the human immunodeficiency virus (HIV). LC were shown to be sensitive to in vitro infection by HIV1. They could be generated in vitro by culturing CD34+ haematopoietic progenitors with GM-CSF+TNF alpha. In this study, we tested the sensitivity to HIV1 infection of in vitro generated LC throughout their differentiation and we investigated the effect of such an infection on in vitro differentiation. Phenotypic controls were performed using FACS analysis on day 6 for the presence of a CD1a+ cell population, and differentiation was assessed by transmission electron microscopy on day 13 for the presence of Birbeck granules. CD34+ cells were purified from cord blood mononuclear cells by magnetic separation. Cell suspensions were infected with either a T-lymphotropic, syncytium-inducing isolate (HXB2) or a macrophage-tropic, non-syncytium-inducing isolate (Ba-L). Viral particle release was measured by p24 antigen production in the culture supernatant. A high level of p24 production was noted on day 13 of postinfection only when infection was carried out with Ba-L isolate on cells generated after 6 days in culture with GM/CSF+TNF alpha. No infection of CD34+ progenitor cells was obtained either with Ba-L isolate or HXB2. The sensitivity of Langerhans cell/dendritic cell (LC/DC) precursors to NSI isolate (Ba-L) seemed to coincide with the early stage of differentiation (CD1a antigen appearance). The infection did not alter the differentiation of in vitro generated LC, which presented their specific ultrastructural marker of epidermal environment, i.e. Birbeck granules from day 15 of the culture as compared to control culture. These results highlight the HIV infectibility of a differentiated population of LC/DC generated in vitro from CD34+ progenitors.

A simple procedure to generate chimeric Pr55gag virus-like particles expressing the principal neutralization domain of human immunodeficiency virus type 1

The Pr55gag human immunodeficiency virus type 1 (HIV-1) precursor protein that is capable of auto-assembling was used as a carrier for a consensus sequence of the principal neutralization domain (PND) of the HIV-1 envelope. For this purpose, a modified HIV-1 gag gene with deletion of the sequence encoding a previously described p24 epitope (amino acids 196-228 of Pr55gag) was first obtained using PCR with degenerate primers, and then cloned. This deleted gag gene allowed in a second time the insertion of a synthetic oligonucleotide cassette encoding the North American/European consensus PND precisely in place of the p24 epitope. The chimeric gene was then inserted into a baculovirus transfer vector and expressed in insect cells. The construct formed 100-140 nm virus-like particles that were released into the extracellular medium. The use of a serum-free medium that supports growth of insect cells facilitated the downstream purification of the extracellular particles. The chimeric particles were recognized by monoclonal antibodies directed to V3 by Western blot but not by immune electron microscopy, suggesting that, although the inserted sequence was still antigenic it was not exposed at the surface of the particles. The results show the ability of Pr55gag to serve as a carrier for easy insertion, in a precisely defined region, of selected epitopes of gp120 surface envelope protein, and to still auto-assemble in virus-like particles. However, the data indicate that exposed epitopes of the mature p24 protein are not presented similarly in the Pr55 precursor, and therefore that different constructs with various insertions in different places must be generated. Such constructs offer an attractive approach for HIV vaccine development and will need evaluation for both antigenicity and immunogenicity.