Expression and purification of p24, the core protein of HIV, using a baculovirus-insect cell expression system

Computational prediction of antifungal peptides via Chou’s PseAAC and SVM

With the increase in immunocompromised patients in the recent years, fungal infections have emerged as new and serious threat in hospitals. This, and the insufficiency of current antifungal therapies alongside their toxic effects on patients, has led to the increased interest in seeking new antifungal peptides. In the present study, we have developed a prediction method for screening of antifungal peptides. For this, we have chosen Chou’s pseudo amino acid composition (PseAAC) to translate peptide sequences into numeric values. Thus, the SVM classifier was performed for binomial classification of antifungal peptides. The performance of the classifier was evaluated via ten-fold cross-validation and an independent dataset. For further validation of the model developed, 22 P24-derived peptides were predicted using the classifier and in vitro assays were performed on the three peptides with the highest prediction score. The results showed that the PseAAC [Formula: see text] SVM method is able to predict AFPs with ACC of 94.76%. In vitro results also validate the SEN and SPC of the classifier. The results suggest that the computational approach used in this study is highly efficient for prediction of antifungal peptides, which can save time and money in AFP screening and synthesis of novel peptides.

Production and purification of polymerization-competent HIV-1 capsid protein p24 (CA) in NiCo21(DE3) Escherichia coli

Background

HIV genome is packaged and organized in a conical capsid, which is made up of ~1,500 copies of the viral capsid protein p24 (CA). Being a primary structural component and due to its critical roles in both late and early stages of the HIV replication cycle, CA has attracted increased interest as a drug discovery target in recent years. Drug discovery studies require large amounts of highly pure and biologically active protein. It is therefore desirable to establish a simple and reproducible process for efficient production of HIV-1 CA.

Result

In this work, 6-His-tagged wild type CA from HIV-1 (NL4.3) was expressed in rare tRNA-supplemented NiCo21(DE3) Escherichia coli, and its production was studied in shake flask culture condition of expression. Influences of various key cultivation parameters were examined to identify optimal conditions for HIV-1 CA production. It was found that a culture temperature of 22°C and induction with 0.05 mM IPTG at the early stage of growth were ideal, leading to a maximum biomass yield when grown in Super broth supplemented with 1% glucose. With optimized culture conditions, a final biomass concentration of ~27.7 g L^-1 (based on optical density) was obtained in 12 hours post-induction, leading to a yield of about ~170 mg L^-1 HIV-1 CA. A two-step purification strategy (chitin beads + IMAC) was employed, which efficiently removed metal affinity resin-binding bacterial proteins that contaminate recombinant His-tagged protein preparation, and resulted in highly pure HIV-1 CA. The purified protein was capable of polymerization when tested in an in vitro polymerization assay.

Conclusions

By using this optimized expression and purification procedure, milligram amounts of highly pure and polymerization-competent recombinant HIV-1 CA can be produced at the lab-scale and thus used for further biochemical studies.

Immunogenicity of chloroplast-derived HIV-1 p24 and a p24-Nef fusion protein following subcutaneous and oral administration in mice

High-level expression of foreign proteins in chloroplasts of transplastomic plants provides excellent opportunities for the development of oral vaccines against a range of debilitating or fatal diseases. The HIV-1 capsid protein p24 and a fusion of p24 with the negative regulatory protein Nef (p24-Nef) accumulate to ∼4% and ∼40% of the total soluble protein of leaves of transplastomic tobacco (Nicotiana tabacum L.) plants. This study has investigated the immunogenicity in mice of these two HIV-1 proteins, using cholera toxin B subunit as an adjuvant. Subcutaneous immunization with purified chloroplast-derived p24 elicited a strong antigen-specific serum IgG response, comparable to that produced by Escherichia coli-derived p24. Oral administration of a partially purified preparation of chloroplast-derived p24-Nef fusion protein, used as a booster after subcutaneous injection with either p24 or Nef, also elicited strong antigen-specific serum IgG responses. Both IgG1 and IgG2a subtypes, associated with cell-mediated Th1 and humoral Th2 responses, respectively, were found in sera after subcutaneous and oral administration. These results indicate that chloroplast-derived HIV-1 p24-Nef is a promising candidate as a component of a subunit vaccine delivered by oral boosting, after subcutaneous priming by injection of p24 and/or Nef.

High level soluble expression, one-step purification and characterization of HIV-1 p24 protein

Background

P24 protein is the major core protein of HIV virus particle and has been suggested as a specific target for antiviral strategies. Recombinant p24 protein with natural antigenic activity would be useful for various studies, such as diagnostic reagents and multi-component HIV vaccine development. The aim of this study was to express and purify the p24 protein in soluble form in E.coli.

Results

According to the sequence of the p24 gene, a pair of primers was designed, and the target sequence of 700 bp was amplified using PCR. The PCR product was cloned into pQE30 vector, generating the recombinant plasmid pQE30-p24. SDS-PAGE analysis showed that the His-tagged recombinant p24 protein was highly expressed in soluble form after induction in E. coli strain BL21. The recombinant protein was purified by nickel affinity chromatography and used to react with HIV infected sera. The results showed that the recombinant p24 protein could specifically react with the HIV infected sera. To study the immunogenicity of this soluble recombinant p24 protein, it was used to immunize mice for the preparation of polyclonal antibody. Subsequent ELISA and Western-Blot analysis demonstrated that the p24 protein had proper immunogenicity in inducing mice to produce HIV p24 specific antibodies.

Conclusion

In this work, we report the high level soluble expression of HIV-1 p24 protein in E. coli. This soluble recombinant p24 protein specifically react with HIV infected sera and elicit HIV p24 specific antibodies in mice, indicating this soluble recombinant p24 protein could be a promising reagent for HIV diagnosis.

Plastid transformation of high-biomass tobacco variety Maryland Mammoth for production of human immunodeficiency virus type 1 (HIV-1) p24 antigen

Chloroplast transformation of the high-biomass tobacco variety Maryland Mammoth has been assessed as a production platform for the human immunodeficiency virus type 1 (HIV-1) p24 antigen. Maryland Mammoth offers the prospect of higher yields of intact functional protein per unit floor area of contained glasshouse per unit time prior to flowering. Two different transformation constructs, pZSJH1p24 (for the insertion of a native p24 cDNA between the rbcL and accD genes) and pZF5 (for the insertion of a chloroplast-codon-optimized p24 gene between trnfM and trnG) were examined for the production of p24. Plants generated with construct pZSJH1p24 exhibited a normal green phenotype, but p24 protein accumulated only in the youngest leaves (up to approximately 350 microg/g fresh weight or approximately 2.5% total soluble protein) and was undetectable in mature leaves. In contrast, some of the plants generated with pZF5 exhibited a yellow phenotype (pZF5-yellow) with detectable p24 accumulation (up to approximately 450 microg/g fresh weight or approximately 4.5% total soluble protein) in all leaves, regardless of age. Total protein in pZF5-yellow leaves was reduced by approximately 40%. The pZF5-yellow phenotype was associated with recombination between native and introduced direct repeat sequences of the rbcL 3' untransformed region in the plastid genome. Chloroplast-expressed p24 was recognized by a conformation-dependent monoclonal antibody to p24, and p24 protein could be purified from pZF5-yellow leaves using a simple procedure, involving ammonium sulphate precipitation and ion-exchange chromatography, without the use of an affinity tag. The purified p24 was shown to be full length with no modifications, such as glycosylation or phosphorylation, using N-terminal sequencing and mass spectrometry.

HIV-1 p24-immunoglobulin fusion molecule: a new strategy for plant-based protein production

We describe the engineering of a human immunodeficiency virus-1 (HIV-1) p24-immunoglobulin A (IgA) antigen-antibody fusion molecule for therapeutic purposes and its enhancing effect on fused antigen expression in tobacco plants. Although many recombinant proteins have been expressed in transgenic plants as vaccine candidates, low levels of expression are a recurring problem. In this paper, using the HIV p24 core antigen as a model vaccine target, we describe a strategy for increasing the yield of a recombinant protein in plants. HIV p24 antigen was expressed as a genetic fusion with the alpha2 and alpha3 constant region sequences from human Ig alpha-chain and targeted to the endomembrane system. The expression of this fusion protein was detected at levels approximately 13-fold higher than HIV p24 expressed alone, and a difference in the behaviour of the two recombinant proteins during trafficking in the plant secretory pathway has been identified. Expressing the antigen within the context of alpha-chain Ig sequences resulted in the formation of homodimers and the antigen was correctly recognized by specific antibodies. Furthermore, the HIV p24 elicited T-cell and antibody responses in immunized mice. The use of Ig fusion partners is proposed as a generic platform technology for up-regulating the expression of antigens in plants, and may represent the first step in a strategy to design new vaccines with enhanced immunological properties.

Parameters influencing measurement of the Gag antigen-specific T-proliferative response to HIV type 1 infection

We have analyzed factors that might influence the in vitro quantitation of the T-proliferative response to HIV-1 Gag antigens, a common and increasingly used clinical measurement of helper T cell function in the context of HIV-1 infection. We have compared the rate and extent of T cell proliferation in freshly prepared and previously frozen PBMC samples, and have concluded that frozen cells can be used successfully; we have assessed whether the suppression of any HIV-1 replication in the PBMC cultures affects the extent of T cell proliferation; we have studied which forms of the Gag antigens are the most efficient at inducing T cell proliferation. From the latter experiments, we conclude that Gag proteins that include p17, and perhaps also p7, sequences flanking the central p24 capsid protein, are better stimulants than proteins that comprise only p24 sequences.

A molecular determinant of human immunodeficiency virus particle assembly located in matrix antigen p17

We report single-point mutations that are located in the matrix protein domain of the gag gene of human immunodeficiency virus type 1 and that prevent Gag particle formation. We show that mutations of p17 that abolish human immunodeficiency virus particle assembly also prevent the dimerization of p17 protein, as measured directly by a protein-protein binding assay. In the three-dimensional structure of p17, mutations that abolish dimerization are located in a single alpha helix that forms part of a fingerlike projection from one side of the molecule. Peptides derived from this region of p17 also reduce the level of p17 dimer when they are added to p17-expressing cells and compete for p17 self-association when present in protein-protein binding assays. We propose that the dimerization of the Gag precursor that occurs by the interdigitation of alpha helices on adjacent matrix molecules is a key stage in virion assembly and that the prevention of such an interaction is the molecular basis of particle misassembly.

Production and purification of recombinant African swine fever virus attachment protein p12

The conditions for cultivation of Spodoptera frugiperda (Sf9) insect cells for production of recombinant baculoviruses have been studied, to scale-up and improve the efficiency of the process for production of the African swine fever virus attachment protein p12 in the baculovirus expression system. It was shown that the total virus and recombinant protein production in insect cells infected with the Acp12 recombinant baculovirus were slightly dependent on cell density, but largely dependent on the serum concentration, in the case of suspended cells, but not in static monolayer cultures. The yield of recombinant protein p12 exceeded 50 mg per 1 of 2 x 10(9) cells, representing more than 10% of total cell proteins, a level > 20-fold higher than that observed with other eukaryotic expression systems. The presence of p12 in the cytoplasmic fraction of infected cells has allowed the purification of the protein by a simple two-step procedure of aqueous phase partition and octyl-glucoside solubilization. The recombinant protein p12 was able to inhibit, in a dose-dependent manner, the African swine fever virus production in swine macrophages infected with a number of different virus isolates, including attenuated, virulent, highly passaged on tissue culture, and non-haemadsorbing strains, indicating a fundamental role for p12 in the early interaction of the virus with the natural target cell receptors. However, pigs immunized with purified recombinant p12 did not develop protective immunity against African swine fever.

A recombinant human immunodeficiency virus type-1 capsid protein (rp24): its expression, purification and physico-chemical characterization

An expression system has been established in Escherichia coli to facilitate the preparation of the HIV-1 capsid protein in amounts sufficient for structural analysis. A plasmid vector pTCA5, containing the gene for the recombinant HIV-1 capsid protein rp24 under the control of the lambda-PR-promoter, was constructed which gave an expression product that spanned 234 amino acid residues. It differs at the N-terminus from the authentic sequence in that the residues Pro-Ile- are replaced by Met-Asn-Ser-Ala-Met-. Recombinant p24 was produced, as inclusion bodies in E. coli LE392 containing pTCA5, at a level of approximately 15% of the total cellular protein. After dissolution of the inclusion bodies in the acidic urea system, the protein was easily reconstituted in a soluble state by dialysis. The yield of reconstituted and purified protein was 12 mg per liter in rich medium. Recombinant rp24 consists of about 40% alpha-helix and 10% beta-sheet from circular dichroism measurements and the two cysteine residues, within the rp24 sequence, are bridged by a disulfide bond.

The use of baculoviruses as expression vectors

The use of recombinant baculoviruses as high level expression systems is becoming more and more popular. This review aims to provide a summary of the impact of this expression system in biochemistry and biotechnology, highlighting important advances that have been made utilizing the system. The potential of newly developed multiple baculovirus expression systems to enable the reconstruction of complex biological molecules and processes is also reviewed.

Murine HIV-1 p24 specific T lymphocyte activation by different antigen presenting cells: B lymphocytes from immunized mice present core protein to T cells

Mice were injected with three doses of baculovirus-produced recombinant HIV-1 p24 core protein in alum adjuvant. CD4 positive T lymphocytes from immunized animals proliferated in vitro in the presence of antigen and peritoneal macrophages (Mps) or splenic dendritic cells (DCs) from non-immunized mice as antigen presenting cells (APCs). DCs were approximately three times more efficient than Mps on a cell for cell basis. No synergy was observed between Mps and DCs in this system. B lymphocytes from immunized animals also presented p24 antigen to the specific T cells. Mps did synergize with B cells to enhance the level of T lymphocyte proliferation. This may have implications for the induction of specific immune responses to pathogens after administration of single protein vaccines.

Development of a sensitive ELISA for HIV-1 p24 antigen using a fluorogenic substrate for monitoring HIV-1 replication in vitro

A two-site sandwich fluorescent-ELISA was optimized for the detection of HIV-1 p24 antigen produced by lymphoid cells infected with HIV-1 in vitro. To improve the sensitivity of the ELISA, a combination of streptavidin-beta-galactosidase and a fluorogenic substrate (4-methylumbelliferyl-beta-D-galactopyranoside) was employed for the enzymatic detection stage. Using recombinant p24 as standard antigen, a two-step assay detected as little as 0.7 pg/ml (3.10(-14) M) with an upper limit of 10,000 pg/ml. This detection range (approx. 50-70-times greater than ELISAs using a chromogenic detection) permitted an accurate and straightforward quantitation of p24 in culture supernatants. Overall, the fluorescent-ELISA had increased detectability, sensitivity and efficiency over existing ELISAs for HIV-1 p24.

Assembly of recombinant human immunodeficiency virus type 1 capsid protein in vitro

The capsid protein (CA) (p24) of human immunodeficiency virus (HIV) type 1 expressed in Escherichia coli and purified to greater than 90% homogeneity was used to examine assembly in vitro and to probe the nature of interactions involved in the formation of capsid structures. The protein was detected in dimeric and oligomeric forms as indicated by molecular size measurements by gel filtration column chromatography, sedimentation through sucrose, and nondenaturing gel electrophoresis. Chemical cross-linking of CA molecules was observed with several homobifunctional reagents. Oligomer size was dependent on cross-linker concentration and exhibited a nonrandom pattern in which dimers and tetramers were more abundant than trimers and pentamers. Oligomers as large as dodecamers were detected in native polyacrylamide gels. These were stable in solutions of high ionic strength or in the presence of nonionic detergent, indicating that strong interactions were involved in oligomer stabilization. Limited tryptic digestion converted the putative dodecamers to octamers, suggesting that a region involved in CA protein multimerization was exposed in the structure. This region was mapped to the central portion of the protein. The recombinant CA proteins assembled in vitro into long rodlike structures and were disassembled into small irregular spheres by alterations in ionic strength and pH. The observation that assembly and disassembly of purified HIV type 1 CA protein can be induced in vitro suggests an approach for identifying possible control mechanisms involved in HIV viral core assembly.

Thermodynamic and kinetic analysis of sCD4 binding to HIV-1 virions and of gp120 dissociation

Kinetic and thermodynamic aspects of the binding of sCD4 to intact virions of human immunodeficiency virus type 1 (HIV-1 RF), and of the subsequent induction of gp120 dissociation were studied. sCD4 binding to virions at 4 and 37 degrees C is half-maximal at approximately 40 and 10 nM, respectively. The transition between low-affinity and high-affinity binding of sCD4 to virions occurs over a narrow temperature range between 20 and 25 degrees C. Shedding of gp120 from virions after sCD4 binding is also temperature dependent, being initiated above approximately 20 degrees C. The minimum temperatures for the sCD4 affinity transition and gp120 shedding are, therefore, similar and we suggest how the two processes might be related mechanistically.