Expression and purification of turkey coronavirus nucleocapsid protein in Escherichia coli

Analysis of preferred codon usage in the coronavirus N genes and their implications for genome evolution and vaccine design

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The nucleotide variations among the N genes of 13 different coronaviruses (CoVs) were interpreted.

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Overall, 18 amino acids observed with varying preferred codons.

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The effective number of codon values ranged from 40.43 to 53.85, revealing a slight codon bias.

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A highly significant correlation between GC3s and ENc values was observed in porcine epidemic diarrhea CoV, followed by Middle East respiratory syndrome CoV.

The nucleocapsid (N) protein of a coronavirus plays a crucial role in virus assembly and in its RNA transcription. It is important to characterize a virus at the nucleotide level to discover the virus’s genomic sequence variations and similarities relative to other viruses that could have an impact on the functions of its genes and proteins. This entails a comprehensive and comparative analysis of the viral genomes of interest for preferred nucleotides, codon bias, nucleotide changes at the 3^rd position (NT3s), synonymous codon usage and relative synonymous codon usage. In this study, the variations in the N proteins among 13 different coronaviruses (CoVs) were analysed at the nucleotide and amino acid levels in an attempt to reveal how these viruses adapt to their hosts relative to their preferred codon usage in the N genes. The results revealed that, overall, eighteen amino acids had different preferred codons and eight of these were over-biased. The N genes had a higher AT% over GC% and the values of their effective number of codons ranged from 40.43 to 53.85, indicating a slight codon bias. Neutrality plots and correlation analyses showed a very high level of GC3s/GC correlation in porcine epidemic diarrhea CoV (pedCoV), followed by Middle East respiratory syndrome-CoV (MERS CoV), porcine delta CoV (dCoV), bat CoV (bCoV) and feline CoV (fCoV) with r values 0.81, 0.68, -0.47, 0.98 and 0.58, respectively. These data implied a high rate of evolution of the CoV genomes and a strong influence of mutation on evolutionary selection in the CoV N genes. This type of genetic analysis would be useful for evaluating a virus’s host adaptation, evolution and is thus of value to vaccine design strategies.

Virus Neutralization Assay for Turkey Coronavirus Infection

Turkey coronavirus (TCoV) infection induces the production of protective antibodies against the sequent exposure of TCoV. Serological tests to determine TCoV-specific antibodies are critical to evaluate previous exposure to TCoV in the turkey flocks and differentiate serotypes from different isolates or strains. A specific virus neutralization assay using embryonated turkey eggs and immunofluorescent antibody assay for determining TCoV-specific neutralizing antibodies is described in this chapter. Virus neutralization titer of turkey serum from turkeys infected with TCoV is the dilution of serum that can inhibit TCoV infection in 50 % of embryonated turkey eggs. Virus neutralization assay for TCoV is useful to monitor the immune status of turkey flocks infected with TCoV for the control of the disease.

Antibody-Capture Enzyme-Linked Immunosorbent Assay for Detection of Antibody to Turkey Coronavirus Using Infectious Bronchitis Virus or Recombinant Nucleocapsid Protein as Coating Antigen

Turkey coronavirus (TCoV) infection continues to threaten turkey industry. Because specific treatment and effective vaccination program are not available, rapid and cost-effective detection of antibodies to TCoV infection is an important control measure to monitor the disease status in the fields. Two antibody-capture enzyme-linked immunosorbent assay (ELISA) procedures for detection of antibodies to TCoV are outlined in this chapter. One ELISA method uses chicken infectious bronchitis coronavirus (IBV) as the coating antigen based on antigenic cross-reactivity between TCoV and IBV. The other method relies on a recombinant TCoV nucleocapsid protein. Both methods are useful for serological diagnosis of TCoV infection in the turkey flocks.

Recombinant Turkey Coronavirus Nucleocapsid Protein Expressed in Escherichia coli

Expression and purification of turkey coronavirus (TCoV) nucleocapsid (N) protein from a prokaryotic expression system as histidine-tagged fusion protein are presented in this chapter. Expression of histidine-tagged fusion N protein with a molecular mass of 57 kDa is induced with isopropyl β-d-1-thiogalactopyranoside (IPTG). The expressed N protein inclusion body is extracted and purified by chromatography on nickel-agarose column to near homogeneity. The protein recovery can be 10 mg from 100 ml of bacterial culture. The purified N protein is a superior source of TCoV antigen for antibody-capture ELISA for detection of antibodies to TCoV.

Recombinant nucleocapsid protein-based enzyme-linked immunosorbent assay for detection of antibody to turkey coronavirus

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Recombinant TCoV N protein was efficiently produced by a prokaryotic expression system.

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An antibody-capture ELISA was established with the recombinant N protein as coating antigen.

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Recombinant N protein-based ELISA is more sensitive than IBV-based ELISA for anti-TCoV antibody.

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The N protein-based ELISA can be applied for a rapid diagnosis and effective control of outbreaks.

Nucleocapsid (N) protein gene of turkey coronavirus (TCoV) was expressed in a prokaryotic system and used to develop an enzyme-linked immunosorbent assay (ELISA) for detection of antibody to TCoV. Anti-TCoV hyperimmune turkey serum and normal turkey serum were used as positive or negative controls for optimization of the ELISA. Goat anti-turkey IgG (H+L) conjugated with horseradish peroxidase was used as detector antibody. Three hundred and twenty two turkey sera from the field were used to evaluate the performance of ELISA and determine the cut-off point of ELISA. The established ELISA was also examined with serum samples obtained from turkeys experimentally infected with TCoV. Those serum samples were collected at various time intervals from 1 to 63 days post-infection. The optimum conditions for differentiation between anti-TCoV hyperimmune serum and normal turkey serum were recombinant TCoV N protein concentration at 20 μg/ml, serum dilution at 1:800, and conjugate dilution at 1:10,000. Of the 322 sera from the field, 101 were positive for TCoV by immunofluorescent antibody assay (IFA). The sensitivity and specificity of the ELISA relative to IFA test were 86.0% and 96.8%, respectively, using the optimum cut-off point of 0.2 as determined by logistic regression method. Reactivity of anti-rotavirus, anti-reovirus, anti-adenovirus, or anti-enterovirus antibodies with the recombinant N protein coated on the ELISA plates was not detected. These results indicated that the established antibody-capture ELISA in conjunction with recombinant TCoV N protein as the coating protein can be utilized for detection of antibodies to TCoV in turkey flocks.

Immunoreactivity characterisation of the three structural regions of the human coronavirus OC43 nucleocapsid protein by Western blot: implications for the diagnosis of coronavirus infection

Previous studies have reported that a prokaryotic-expressed recombinant nucleocapsid protein (NP) is a suitable reagent for the epidemiological screening of coronavirus infection. In this study, soluble recombinant human coronavirus OC43 (HCoV-OC43) NP was produced to examine the antigenicity of the HCoV-OC43 NP of betacoronavirus. Using the purified recombinant NP as an antigen, a polyclonal antibody from rabbit serum with specificity for HCoV-OC43 NP was generated; this antibody reacts specifically with HCoV-OC43 NP and does not cross-react with other human CoV NPs (including those of SARS-CoV and HCoV-229E) by Western blot. Sera from 26 young adults, 17 middle-aged and elderly patients with respiratory infection, and 15 cord blood samples were also tested. Strong reactivity to the NPs of HCoV-OC43 was observed in 96%, 82%, and 93% of the serum samples from the young adults, respiratory patients, and cord blood samples, respectively. To identify the immunoreactivities of the three structural regions of the NP that are recognised by the rabbit polyclonal antibody and human serum, the antigenicities of three protein fragments, including the N-terminal domain (aa 1-173), the central-linker region (aa 174-300), and the C-terminal domain (aa 301-448), were evaluated by Western blot. The rabbit polyclonal antibody demonstrated greater immunoreactivity to the central-linker region and the C-terminal domain than to the N-terminal domain. Three different patterns for the immunoreactivities of the three structural regions of HCoV-OC43 NP were observed in human serum, suggesting variability in the immune responses that occur during HCoV-OC43 infection in humans. The central-linker region of the NP appeared to be the most highly immunoreactive region for all three patterns observed. The goal of this study was to offer insight into the design of diagnostic tools for HCoV infection.

Recombinant protein-based viral disease diagnostics in veterinary medicine

Identification of pathogens or antibody response to pathogens in human and animals modulates the treatment strategies for naive population and subsequent infections. Diseases can be controlled and even eradicated based on the epidemiology and effective prophylaxis, which often depends on development of efficient diagnostics. In addition, combating newly emerging diseases in human as well as animal healthcare is challenging and is dependent on developing safe and efficient diagnostics. Detection of antibodies directed against specific antigens has been the method of choice for documenting prior infection. Other than zoonosis, development of inexpensive vaccines and diagnostics is a unique problem in animal healthcare. The advent of recombinant DNA technology and its application in the biotechnology industry has revolutionized animal healthcare. The use of recombinant DNA technology in animal disease diagnosis has improved the rapidity, specificity and sensitivity of various diagnostic assays. This is because of the absence of host cellular proteins in the recombinant derived antigen preparations that dramatically decrease the rate of false-positive reactions. Various recombinant products are used for disease diagnosis in veterinary medicine and this article discusses recombinant-based viral disease diagnostics currently used for detection of pathogens in livestock and poultry.

CLONAGEM E EXPRESSÃO DO GENE DA GLICOPROTEÍNA S1 DO VÍRUS DA BRONQUITE INFECCIOSA DAS GALINHAS EM PICHIA PASTORIS

RESUMO Variações genética e antigênica são observadas com frequência elevada entre estirpes do VBIG e envolvem principalmente a glicoproteína S1. Com o objetivo de contribuir com a disponibilidade de ferramentas para o imunodiagnóstico e a imunoprofilaxia da bronquite infecciosa das galinhas foi desenvolvida uma metodologia para expressão recombinante da glicoproteína S1 na levedura Picchia pastoris. O cDNA do gene codificador dessa proteína foi obtido a partir de RNA viral de ovos embrionados infectados com a estirpe M41 do VBIG submetido à transcrição reversa (RT) e reação em cadeia da polimerase (PCR), amplificando-se a sequência codificadora de S1 acrescida de extremidades compatíveis com a clonagem no vetor usado na transformação de leveduras. A indução com metanol resultou na produção de uma proteína detectada como banda única do tamanho previsto, em western-blot, no lisado celular das leveduras transformadas. A expressão em P. pastoris mostrou ser um método eficaz para a produção recombinante da proteína S1 do VBIG, com potencial para utilização em técnicas de imunodiagnóstico da bronquite infecciosa das galinhas.

CLONAGEM, EXPRESSÃO E CARACTERIZAÇÃO DA NUCLEOPROTEÍNA RECOMBINANTE DO VÍRUS DA BRONQUITE INFECCIOSA EM ESCHERICHIA COLI E EM PICHIA PASTORIS

RESUMO O gene da proteína de nucleocapsídeo (1.230 pb) da estirpe M41 do vírus da bronquite infecciosa (VBI) foi amplificado pelas reações de transcrição reversa e em cadeia da polimerase (RT-PCR) e clonado, em seguida, em dois sistemas; pET28a - Escherichia coli e pFLD -Pichia pastoris. Os produtos recombinantes construídos para expressão (pET28a-N ou pFLD-N) foram identificados por análises de PCR e de sequenciamento de nucleotídeos. Os clones transformantes da linhagem BL21 de E. coli e da linhagem GS115 de P. pastoris foram submetidos aos protocolos apropriados de indução. A expressão da proteína N de fusão com etiqueta de poli-histidina e com massa molecular de 54 kDa foi determinada pelas técnicas de SDS-PAGE e de Western blotting, confirmando-se que ambas proteínas N recombinantes apresentaram tamanhos e antigenicidade compatíveis com a proteína N nativa do próprio VBI. O sistema E. coli expressou uma quantidade relevante da proteína N recombinante, enquanto que o sistema P. pastoris produziu uma baixa recuperação dessa proteína recombinante. A proteína N recombinante gerada pelo sistema bacteriano foi purificada em resina de níquel-sepharose. O conjunto de resultados indica que o sistema de expressão constituído por pET28a – E. coli é mais efetivo para produzir a proteína N recombinante do VBI destinada ao uso como antígeno para detectar anticorpos anti-virais específicos em ensaios de imunodiagnóstico para essa infecção viral.

Use of recombinant S1 spike polypeptide to develop a TCoV-specific antibody ELISA

Turkey coronavirus (TCoV) causes diarrhoea in young turkey poults but little is known about its prevalence in the field. To address this, a portion of the S1 region of the spike glycoprotein of TCoV carrying relevant B cell epitopes (amino acid positions 54-395) was cloned and expressed in Escherichia coli. This protein was purified and used to develop an indirect ELISA for detection of antibodies against TCoV. Using experimentally derived positive and negative turkey serum samples this ELISA showed high sensitivity (95%) and specificity (92%) for TCoV. To further evaluate the potential of the ELISA, 360 serum samples from commercial turkey farms in Ontario were tested for TCoV-specific antibodies using the recombinant TCoV ELISA. High seroprevalence of TCoV was found with 71.11% of breeders and 56.67% of meat turkeys testing seropositive. Although there was significant positive correlation with a TCoV-N protein-based ELISA, there was little to no correlation with the whole IBV antigen-based ELISA when field sera were tested for antibodies against TCoV.

Seroprevalence of turkey coronavirus in North American turkeys determined by a newly developed enzyme-linked immunosorbent assay based on recombinant antigen

Turkey coronavirus (TCoV) causes diarrhea in young turkey poults, but little is known about its prevalence in the field. To address this, the complete nucleocapsid gene was cloned and expressed in Escherichia coli. Expressed nucleocapsid gene produced two distinct proteins (52 and 43 kDa); their specificity was confirmed by Western blotting using two different monoclonal antibodies. Recombinant N protein was purified and used as an antigen to develop an enzyme-linked immunosorbent assay (ELISA) for the serological detection of TCoV that was then validated using experimentally derived turkey serum. The N-based ELISA showed (97%) sensitivity and (93%) specificity for TCoV, which was significantly higher than an infectious bronchitis coronavirus-based commercial test for TCoV. To assess the utility of this recombinant ELISA, 360 serum samples from turkey farms in Ontario, Canada, and 81 serum samples from farms in Arkansas were tested for TCoV-specific antibodies. A high seroprevalence of TCoV was found in turkeys from the Ontario farms with 73.9% of breeders and 60.0% of meat turkeys testing seropositive using the N-based ELISA. Similarly, a high field prevalence was found in the turkeys from Arkansas, for which 64.2% of the serum samples tested seropositive.

Serodiagnosis using recombinant nipah virus nucleocapsid protein expressed in Escherichia coli

Nipah virus nucleocapsid (NiV-N) protein was expressed in Escherichia coli and purified by histidine tag-based affinity chromatography. An indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) for human and swine sera and an IgM capture ELISA for human sera were established using the recombinant NiV-N protein as an antigen. One hundred thirty-three suspected patient sera and 16 swine sera were used to evaluate the newly established ELISA systems in comparison with the CDC inactivated-virus-based ELISA systems. For the human sera, the NiV-N protein-based indirect IgG ELISA had a sensitivity of 98.6% and a specificity of 98.4%, and the NiV-N protein-based IgM capture ELISA had a sensitivity of 91.7% and a specificity of 91.8%, with reference to the CDC ELISA systems. The NiV-N-based IgM ELISA was found to be more sensitive than the inactivated-virus-based ELISA in that it captured eight additional cases. For the swine sera, the two test systems were in 100% concordance. Our data indicate that the Nipah virus nucleocapsid protein is a highly immunogenic protein in human and swine infections and a good target for serodiagnosis. Our NiV-N protein-based ELISA systems are useful, safe, and affordable tools for diagnosis of Nipah virus infection and are especially fit to be used in large-scale epidemiological investigations and to be applied in developing countries.

Purification of the extra-cellular domain of Nipah virus glycoprotein produced in Escherichia coli and possible application in diagnosis

The glycoprotein (G) of Nipah virus (NiV) is important for virus infectivity and induction of the protective immunity. In this study, the extra-cellular domain of NiV G protein was fused with hexahistidine residues at its N-terminal end and expressed in Escherichia coli. The expression under transcriptional regulation of T7 promoter yielded insoluble protein aggregates in the form of inclusion bodies. The inclusion bodies were solubilized with 8 M urea and the protein was purified to homogeneity under denaturing conditions using nickel–nitrilotriacetic acid (Ni–NTA) affinity chromatography. The denatured protein was renatured by gradual removal of the urea. Light scattering analysis of the purified protein showed primarily monodispersity. The purified protein showed significant reactivity with the antibodies present in the sera of NiV-infected swine, as demonstrated in Western blot analysis and enzyme-linked immunosorbent assay (ELISA). Taken together, the data indicate the potential usefulness of the purified G protein for structural or functional studies and the development of immunoassay for detection of the NiV antibodies.