Production and diagnostic application of a purified, E. coli-expressed, serological-specific chicken anaemia virus antigen VP3

Cytotoxic Effects of a Novel tagged Apoptin on Breast Cancer Cell Lines

Backgrounds

Apoptin can induce tumor cell-specific apoptosis in a broad range of human tumor cells and is a potential anticancer therapeutic candidate to kill tumor cells.

Materials and Methods

We designed two structures of apoptin fusion protein, SUMO-PTD4-Apoptin, and PTD4-Apoptin. To express these fusion proteins, E. coli BL21(DE3) was employed. MTT assay, Flow cytometry, and cell cycle analysis were used to investigate the function of proteins on two breast cancer cell lines (MDA-MB-231 and MCF-7) and MCF 10A cell line (as normal cells).

Results

Expression of the recombinant SUMO-PTD4-Apoptin and PTD4-Apoptin in E. coli BL21(DE3) was successful. MTT assay results showed that the IC50 was 6.4 µg/ml for SUMO-PTD4-Apoptin in MDA-MB-231 and was 9.3 after 24 h of treatment in MCF-7. The specific cytotoxicity in both cell lines is significant in comparison with MCF-10A, which is used as a normal cell line (IC50 = 29.4). The IC50 for PTD4-Apoptin was 11.07 µg/ml after 24 h of treatment in MDA-MB-231, while the IC50 of PTD4-Apoptin for MCF7 cells was not significantly different from normal cells. The flow cytometry analysis displayed a significant increment in the apoptosis and late apoptosis number in the MDA-MB-231 cells after treatment with SUMO-PTD4-Apoptin and PTD4-Apoptin protein. PTD4-Apoptin and SUMO-PTD4-Apoptin treatment of MDA-MB-231 cells caused a noteworthy increase in the G0-G1 phase and a reduction in the cell population of S and M/G2.

Conclusion

This study demonstrates that the fusion of PTD4-Apoptin to SUMO-PTD4-Apoptin could provide an effective method to help enhance the expression and solubility of heterologous Apoptin in E. coli. BL21 (DE3).

Effective production of recombinant Δ60VP1 chicken anemia virus protein in Escherichia coli and its application to a serodiagnostic indirect ELISA

Chicken anemia virus (CAV) causes severe anemia and immunosuppression in chickens. VP1 is the main capsid protein, and is suitable for diagnostic kit development, however, it has 24 arginine residues in the first forty N-terminal amino acids of the protein causing toxicity to bacteria leading to reduced prokaryotic expression. In this study, a 60 amino acid N-terminally truncated VP1 (Δ60VP1) which removes the toxic region was expressed in Escherichia coli and the resultant insoluble recombinant protein was purified by Ni-NTA affinity chromatography with anionic denaturing detergents. The high amounts of purified Δ60VP1 produced (150 mg/L) retained appropriate antigenicity and the antigen was used to develop an indirect enzyme-linked immunosorbent assay (ELISA) for serological diagnosis of CAV. One hundred fifty-two chicken serum samples (n = 152) were evaluated using the newly developed Δ60VP1 indirect ELISA (cutoff value = 7.58 % S/P). The sensitivity and specificity of the Δ60VP1 indirect ELISA were 87.50 % and 95.31 %, respectively, while the agreement between the Δ60VP1 indirect ELISA and the commercial IDEXX CAV ELISA was 90.79 % (kappa = 0.814). In this study, we have developed an alternative VP1 production platform in E. coli by truncating the N-terminal 60 amino acids (Δ60VP1) and using anionic denaturing detergents during the purification to successfully solubilize the insoluble Δ60VP1. The antigen was purified with high yield and good immunoreactivity, and an indirect ELISA was developed. The assay could potentially be applied to large-scale CAV serosurveillance.

High yield production of pigeon circovirus capsid protein in the E. coli by evaluating the key parameters needed for protein expression

Background

Pigeon circovirus (PiCV) is considered to be a viral agent central to the development of young pigeon disease syndrome (YPDS). The Cap protein, a structural protein encoded by the cap (or C1) gene of PiCV, has been shown to be responsible for not only capsid assembly, but also has been used as antigen for detecting antibody when the host is infected with PiCV. The antigenic characteristics of the Cap protein potentially may allow the development of a detection kit that could be applied to control PiCV infection. However, poor expression and poor protein solubility have hampered the production of recombinant Cap protein in the bacteria. This study was undertaken to develop the optimal expression of recombinant full-length Cap protein of PiCV using an E. coli expression system.

Results

The PiCV cap gene was cloned and fused with different fusion partners including a His-tag, a GST-tag (glutathioine-S-transferase tag) and a Trx-His-tag (thioredoxin-His tag). The resulting constructs were then expressed after transformation into a number of different E. coli strains; these then had their protein expression evaluated. The expression of the recombinant Cap protein in E. coli was significantly increased when Cap protein was fused with either a GST-tag or a Trx-His tag rather than a His-tag. After various rare amino acid codons presented in the Cap protein were optimized to give the sequence rCap_opt, the expression level of the GST-rCap_opt in E. coli BL21(DE3) was further increased to a significant degree. The highest protein expression level of GST-rCap_opt obtained was 394.27 ± 26.1 mg/L per liter using the E. coli strain BL21(DE3)-pLysS. Moreover, approximately 74.5% of the expressed GST-rCap_opt was in soluble form, which is higher than the soluble Trx-His-rCap_opt expressed using the BL21(DE3)-pLysS strain. After purification using a GST affinity column combined with ion-exchange chromatography, the purified recombinant GST-rCap_opt protein was found to have good antigenic activity when tested against PiCV-infected pigeon sera.

Conclusions

These findings shows that the E. coli-expressed full-length PiCV Cap protein has great potential in terms of large-scaled production and this should allow in the future the development of a serodiagnostic kit that is able to clinically detect PiCV infection in pigeons.

Full-Genome Sequence of Chicken Anemia Virus Strain GXC060821, Isolated from a Guangxi Sanhuang Chicken

We report here the complete genomic sequence of a novel chicken anemia virus strain GXC060821, isolated from a Sanhuang chicken in Guangxi Province of southern China. The complete genome of GXC060821 was sequenced. The full-length of GXC060821 is 2,292 bp and contains three overlapping open reading frames (ORFs). A comparison of the complete sequences and the deduced amino acid sequences of GXC060821 with 31 other published chicken anemia virus sequences showed that the homologies of the nucleotides are 96.1% to 98.5% and the homologies of the deduced amino acid sequences are 89.8% to 94.2%. Phylogenetic tree analysis indicated that GXC060821 is closely related to the two Chinese strains, TJBD40 (accession no. AY843527) and LF4 (accession no. AY839944), and it has a distant relationship with the American isolate 98D06073 (accession no. AF311900). This report will help to understand the epidemiology and molecular characteristics of chicken anemia virus in a Guangxi Sanhuang chicken.

Expression and characterization of highly antigenic domains of chicken anemia virus viral VP2 and VP3 subunit proteins in a recombinant E. coli for sero-diagnostic applications

Background

Chicken anemia virus (CAV) is an important viral pathogen that causes anemia and severe immunodeficiency syndrome in chickens worldwide. Generally, CAV infection occurs via vertical transmission in young chicks that are less than two weeks old, which are very susceptible to the disease. Therefore, epidemiological investigations of CAV infection and/or the evaluation of the immunization status of chickens is necessary for disease control. Up to the present, systematically assessing viral protein antigenicity and/or determining the immunorelevant domain(s) of viral proteins during serological testing for CAV infection has never been performed. The expression, production and antigenic characterization of CAV viral proteins such as VP1, VP2 and VP3, and their use in the development of diagnostic kit would be useful for CAV infection prevention.

Results

Three CAV viral proteins VP1, VP2 and VP3 was separately cloned and expressed in recombinant E. coli. The purified recombinant CAV VP1, VP2 and VP3 proteins were then used as antigens in order to evaluate their reactivity against chicken sera using indirect ELISA. The results indicated that VP2 and VP3 show good immunoreactivity with CAV-positive chicken sera, whereas VP1 was found to show less immunoreactivity than VP2 and VP3. To carry out the further antigenic characterization of the immunorelevant domains of the VP2 and VP3 proteins, five recombinant VP2 subunit proteins (VP2-435N, VP2-396N, VP2-345N, VP2-171C and VP2-318C) and three recombinant VP3 subunit proteins (VP3-123N, VP3-246M, VP3-366C), spanning the defined regions of VP2 and VP3 were separately produced by an E. coli expression system. These peptides were then used as antigens in indirect ELISAs against chicken sera. The results of these ELISAs using truncated recombinant VP2 and VP3 subunit proteins as coating antigen showed that VP2-345N, VP2-396N and VP3-246M gave good immunoreactivity with CAV-positive chicken sera compared to the other subunit proteins. Moreover, the VP2-396N and VP2-345 based ELISAs had better sensitivity (97.5%) and excellent specificity (100%) during serodiagnosis testing using a mean plus three standard deviations cut-off. The VP3-246M based ELISA showed a sensitivity of 85% and a specificity of 100% at the same cut-off value.

Conclusions

This is the first report to systematically assess the antigenic characteristics of CAV viral proteins for sero-diagnosis purposes. Purified recombinant VP2-396N and VP2-345N subunit proteins, which span defined regions of VP2, were demonstrated to have good antigenicity and higher sensitivities than VP3-246M and were able to recognize CAV-positive chicken serum using an ELISA assay. The defined antigenicity potential of these chimeric subunit proteins produced by expression in E. coli seem to have potential and could be useful in the future for the development of the CAV diagnostic tests based on a subunit protein ELISA system.

Efficient production of an engineered apoptin from chicken anemia virus in a recombinant E. coli for tumor therapeutic applications

Background

Apoptin, a nonstructural protein encoded by the VP3 gene of chicken anemia virus (CAV), has been shown to not only induce apoptosis when introduced into the precursors of chicken thymocytes, but has been found to specifically kill human cancer cells, tumor cell and transformed cells without affecting the proliferation of normal cells. This tumor-specific apoptotic characteristic of the protein potentially may allow the development of a protein drug that has applications in tumor therapy. However, several major problems, which include poor expression and poor protein solubility, have hampered the production of apoptin in bacteria.

Results

Significantly increased expression of recombinant full-length apoptin that originated from chicken anemia virus was demonstrated using an E. coli expression system. The CAV VP3 gene was fused with a synthetic sequence containing a trans-acting activator of transcription (TAT) protein transduction domain (PTD). The resulting construct was cloned into various different expression vectors and these were then expressed in various E. coli strains. The expression of the TAT-Apoptin in E. coli was significantly increased when TAT-Apoptin was fused with GST-tag rather than a His-tag. When the various rare amino acid codons of apoptin were optimized, the expression level of the GST-TAT-Apoptin_opt in E. coli BL21(DE3) was significantly further increased. The highest protein expression level obtained was 8.33 g/L per liter of bacterial culture after induction with 0.1 mM IPTG for 4 h at 25 °C. Moreover, approximately 90% of the expressed GST-TAT-Apoptin_opt under these conditions was soluble. After purification by GST affinity chromatography, the purified recombinant TAT-Apoptin_opt protein was used to evaluate the recombinant protein’s apoptotic activity on tumor cells. The results demonstrated that the E. coli-expressed GST-TAT-apoptin_opt showed apoptotic activity and was able to induce human premyelocytic leukemia HL-60 cells to enter apoptosis.

Conclusions

On expression in E. coli, purified recombinant TAT-Apoptin_opt that has been fused to a GST tag and had its codons optimized, was found to have great potential. This protein may in the future allow the development of a therapeutic protein that is able to specifically kill tumor cells.

High yield expression in a recombinant E. coli of a codon optimized chicken anemia virus capsid protein VP1 useful for vaccine development

Background

Chicken anemia virus (CAV), the causative agent chicken anemia, is the only member of the genus Gyrovirus of the Circoviridae family. CAV is an immune suppressive virus and causes anemia, lymph organ atrophy and immunodeficiency. The production and biochemical characterization of VP1 protein and its use in a subunit vaccine or as part of a diagnostic kit would be useful to CAV infection prevention.

Results

Significantly increased expression of the recombinant full-length VP1 capsid protein from chicken anemia virus was demonstrated using an E. coli expression system. The VP1 gene was cloned into various different expression vectors and then these were expressed in a number of different E. coli strains. The expression of CAV VP1 in E. coli was significantly increased when VP1 was fused with GST protein rather than a His-tag. By optimizing the various rare amino acid codons within the N-terminus of the VP1 protein, the expression level of the VP1 protein in E. coli BL21(DE3)-pLysS was further increased significantly. The highest protein expression level obtained was 17.5 g/L per liter of bacterial culture after induction with 0.1 mM IPTG for 2 h. After purification by GST affinity chromatography, the purified full-length VP1 protein produced in this way was demonstrated to have good antigenicity and was able to be recognized by CAV-positive chicken serum in an ELISA assay.

Conclusions

Purified recombinant VP1 protein with the gene's codons optimized in the N-terminal region has potential as chimeric protein that, when expressed in E. coli, may be useful in the future for the development of subunit vaccines and diagnostic tests.