The full length cDNA of SARS coronavirus nucleocapsid (N) protein was amplified by PCR and cloned into yeast expression vector pPIC3.5K to generate expression vector pPIC3.5K-SCoVN. The plasmid was linearized and then transformed into P. pastoris (His- Mut+) by electroporation method. His+ Mut+ recombinant strains were screened on G418-RDB and MM/MD plates, and further confirmed by PCR. The influence of various inducing media, dissolved oxygen(DO) and the different final concentration of methanol was subsequently investigated. The results showed that the FBS medium was optimal for recombinant N protein expression and growth of the recombinant strain. The optimal final concentration of methanol is 1% (V/V), and the DO has a significant effect on recombinant N protein expression and growth of recombinant strain. The recombinant N protein expressed was about 6% of the total cell proteins, 410 mg/L of recombinant N protein and 45 OD600 were achieved in shake flask. Western-blot showed that the recombinant N protein had high specificity against mouse-anti-N protein-mAb and SARS positive sera, but had no cross-reaction with normal human sera. The result of scale-up culture in fermemtator demonstrated that 2.5g/L of recombinant N protein and the maximum cell 345 OD600 of were achieved, which was 6.1 times and 7.7 times higher than that in shake flask. So this study provide a basis for further researches on the early diagnosis of SARS and the virus reproduction and pathology reaction of SARS coronavirus.
Cloning, Molecular ; Nucleocapsid Proteins ; biosynthesis ; genetics ; immunology ; Pichia ; genetics ; metabolism ; Recombinant Proteins ; biosynthesis ; genetics ; immunology ; SARS Virus ; genetics

Since the outbreak of corona virus disease 2019 (COVID-19), viral strains have mutated and evolved. Vaccine research is the most direct and effective way to control COVID-19. According to different production mechanisms, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines included inactivated virus vaccine, live attenuated vaccine, mRNA vaccine, DNA vaccine, viral vector vaccine, virus-like particle vaccine and protein subunit vaccine. Among them, viral protein subunit vaccine has a wide application prospect due to its high safety and effectiveness. Viral nucleocapsid protein has high immunogenicity and low variability which could be a new direction for vaccine production. We summarized the current development of vaccine research by reviewing the current progress, vaccine safety and vaccine immune efficiency. It is hoped that the proposed possible development strategies could provide a reference for epidemic prevention work in future.
Humans ; SARS-CoV-2/genetics* ; COVID-19/prevention & control* ; Protein Subunits ; Vaccines, DNA ; Nucleocapsid Proteins

Production of Hepatitis E Virus capsid protein by high cell density culture in recombinant E. coli has been studied in 10L and 30L fermentors. The effects of different factors on growth and producing recombinant protein of E. coli have been studied by batch culture, such as different media, the ratio of phosphate and Magnesium sulfate. Comparison of fermentation performance for recombinant E. coli in different fed-methods culture has been investigated by fed-batch culture. The effects of inducing at different stages of growth and time of inducing on growth and producing recombinant protein, also obtained by fed-batch culture. At last, the solubility of inclusion body in different urea concentrations also has been obtained by fed-batch culture. The results show that the concentration of phosphate and Magnesium sulfate in the optimal media is 80mmol/L and 20mmol/L in batch culture respectively, that induction with 1.0mmol/L IPTG at mid log phase (about 45 OD at 600nm) is suitable for growth and recombinant protein expression, the cells were approaching stationary growth phase and the maximum cell OD at 600nm of 80 was achieved in 5h of fed-batch culture, and the expression level is 29.74%. The results also indicate that the solubility of inclusion body in 4mol/L urea solution induced at 37 degrees C reaches 14mg/mL, over 80% inclusion body was resolved. The culture process achieved in 10L fermentor could be successfully scaled up to 30L fenmentor with good reproducibility.
Bioreactors ; microbiology ; Colony Count, Microbial ; Escherichia coli ; genetics ; metabolism ; Hepatitis E virus ; genetics ; Nucleocapsid Proteins ; biosynthesis ; genetics ; Protein Engineering ; methods ; Recombinant Fusion Proteins ; biosynthesis ; genetics

BACKGROUNDSevere acute respiratory syndrome (SARS) is an infectious disease caused by SARS-CoV. There are no effective antiviral drugs for SARS although the epidemic of SARS was controlled. The aim of this study was to develop an RNAi (RNA interference) approach that specifically targeted the N gene sequence of severe acute respiratory syndrome associated coronavirus (SARS-CoV) by synthesizing short hairpin RNA (shRNA) in vivo, and to assess the inhibitory effect of this shRNA on SARS-CoV N antigen expression.

METHODSThe eukaryotic expression plasmid pEGFP-C1-N, containing SARS-CoV N gene, was co-transfected into 293 cells with either the RNAi plasmid pshRNA-N or unrelated control plasmid pshRNA-HBV-C4. At 24, 48 and 72 hours post transfection, the green fluorescence was observed through a fluorescence microscope. The RNA levels of SARS-CoV N were determined by reverse transcription polymerase chain reaction (RT-PCR). The expression of Green Fluorescent Protein (GFP) and protein N were detected using Western blot.

RESULTSThe vector, pshRNA-N expressing shRNA which targeted the N gene of SARS-CoV, was successfully constructed. The introduction of RNAi plasmid efficiently and specifically inhibited the synthesis of protein N. RT-PCR showed that RNAs of N gene were clearly reduced when the pEGFP-C1-N was cotransfected with pshRNA-N, whereas the control vector did not exhibit inhibitory effect on N gene transcription.

CONCLUSIONSOur results demonstrate that RNAi mediated silencing of SARS-CoV gene could effectively inhibit expression of SARS-CoV antigen, hence RNAi based strategy should be further explored as a more efficacious antiviral therapy of SARS-CoV infection.

Antigens, Viral ; genetics ; Cells, Cultured ; Genetic Vectors ; Green Fluorescent Proteins ; genetics ; Humans ; Nucleocapsid Proteins ; antagonists & inhibitors ; genetics ; RNA Interference ; SARS Virus ; genetics ; immunology ; Severe Acute Respiratory Syndrome ; therapy

BACKGROUNDSeveral coronaviruses establish persistent infections in vitro and in vivo, however it is unknown whether persistence is a feature of the severe acute respiratory syndrome coronavirus (SARS-CoV) life cycle. This study was conducted to investigate viral persistence.

METHODSWe inoculated confluent monolayers of Vero cells with SARS-CoV at a multiplicity of infection of 0.1 TCID50 and passaged the remaining cells every 4 to 8 days for a total of 11 passages. Virus was titrated at each passage by limited dilution assay and nucleocapsid antigen was detected by Western blot and immunofluoresence assays. The presence of viral particles in passage 11 cells was assessed by electron microscopy. Changes in viral genomic sequences during persistent infection were examined by DNA sequencing.

RESULTSCytopathic effect was extensive after initial inoculation but diminished with serial passages. Infectious virus was detected after each passage and viral growth curves were identical for parental virus stock and virus obtained from passage 11 cells. Nucleocapsid antigen was detected in the majority of cells after initial inoculation but in only 10%-40% of cells at passages 2-11. Electron microscopy confirmed the presence of viral particles in passage 11 cells. Sequence analysis at passage 11 revealed fixed mutations in the spike (S) gene and ORFs 7a-8b but not in the nucleocapsid (N) gene.

CONCLUSIONSSARS-CoV can establish a persistent infection in vitro. The mechanism for viral persistence is consistent with the formation of a carrier culture whereby a limited number of cells are infected with each round of virus replication and release. Persistence is associated with selected mutations in the SARS-CoV genome. This model may provide insight into SARS-related lung pathology and mechanisms by which humans and animals can serve as reservoirs for infection.

Animals ; Antigens, Viral ; analysis ; Cercopithecus aethiops ; Microscopy, Electron ; Nucleocapsid Proteins ; analysis ; SARS Virus ; genetics ; growth & development ; Vero Cells

To clarify the pathogenesis of Duck enteritis virus (DEV), the cDNA library of duck's liver infected by DEV and a bait plasmid containing DEV nucleocapsid protein (NP) gene were constructed, then the receptor was screened from the cDNA library plasmid by the yeast two-hybrid system and verified by GST pull-down test. The results showed that the capacity of the primary cDNA library was 1 x 106 CFU with insertion size from 0.5 to 1 kb, and the bait plasmid of pGBKT7-NP showed no self-activation. The receptor reacting with DEV NP in duck liver was initially confirmed as the protein kinase C inhibitor (PKCI). These results provide new clues for further investigation on pathogenesis of DEV.
Alphaherpesvirinae ; pathogenicity ; Animals ; Ducks ; virology ; Gene Library ; Liver ; virology ; Nucleocapsid Proteins ; genetics ; Plasmids ; Receptors, Virus ; analysis ; Two-Hybrid System Techniques

Rice stripe virus (RSV) transmitted by the small brown planthopper causes severe rice yield losses in Asian countries. Although viral nuclear entry promotes viral replication in host cells, whether this phenomenon occurs in vector cells remains unknown. Therefore, in this study, we systematically evaluated the presence and roles of RSV in the nuclei of vector insect cells. We observed that the nucleocapsid protein (NP) and viral genomic RNAs were partially transported into vector cell nuclei by utilizing the importin α nuclear transport system. When blocking NP nuclear localization, cytoplasmic RSV accumulation significantly increased. In the vector cell nuclei, NP bound the transcription factor YY1 and affected its positive regulation to FAIM. Subsequently, decreased FAIM expression triggered an antiviral caspase-dependent apoptotic reaction. Our results reveal that viral nuclear entry induces completely different immune effects in vector and host cells, providing new insights into the balance between viral load and the immunity pressure in vector insects.
Animals ; Cell Nucleus ; Hemiptera/metabolism* ; Insect Vectors/genetics* ; Insecta ; Nucleocapsid Proteins/metabolism* ; Oryza ; Plant Diseases ; Tenuivirus/metabolism* ; Virus Replication

Ebola virus (EBOV) harbors an RNA genome encapsidated by nucleoprotein (NP) along with other viral proteins to form a nucleocapsid complex. Previous Cryo-eletron tomography and biochemical studies have shown the helical structure of EBOV nucleocapsid at nanometer resolution and the first 450 amino-acid of NP (NPΔ451-739) alone is capable of forming a helical nucleocapsid-like complex (NLC). However, the structural basis for NP-NP interaction and the dynamic procedure of the nucleocapsid assembly is yet poorly understood. In this work, we, by using an E. coli expression system, captured a series of images of NPΔ451-739 conformers at different stages of NLC assembly by negative-stain electron microscopy, which allowed us to picture the dynamic procedure of EBOV nucleocapsid assembly. Along with further biochemical studies, we showed the assembly of NLC is salt-sensitive, and also established an indispensible role of RNA in this process. We propose the diverse modes of NLC elongation might be the key determinants shaping the plasticity of EBOV virions. Our findings provide a new model for characterizing the self-oligomerization of viral nucleoproteins and studying the dynamic assembly process of viral nucleocapsid in vitro.
Ebolavirus ; chemistry ; genetics ; metabolism ; Escherichia coli ; genetics ; metabolism ; Gene Expression ; Nucleocapsid ; chemistry ; genetics ; metabolism ; RNA, Viral ; chemistry ; genetics ; metabolism ; Recombinant Proteins ; chemistry ; genetics ; metabolism ; Virus Assembly

:To characterize nucleocapsid (N) protein genes of human respiratory syncytial viruses isolated from children in Beijing and express the N genes in E. coli,seven HRSV strains (three subtype A and four subtype B) were isolated from clinical samples of infants and children with acute respiratory infections and visited the Children's Hospital affiliated to Capital Institute of Pediatrics in Beijing during the period of Jan. 2006 to Mar. Full length of N genes from seven HRSV strains were amplified by reverse-transcription PCR (RT-PCR). The seven PCR amplicons were sequenced after cloning into pUCm-T and the sequences were compared with the N genes from HRSVs in GenBank. N gene was amplified from recombinant plasmid pUCm-N9968 by PCR and then sub-cloned into the prokaryotic expression vector pET30a(+) after digestion with EcoR I and Xho I . The pET30a-N9968 was transformed into E. coli BL21 (DE3) and expressed by inducing with IPTG. Target protein was characterized by SDS-PAGE electrophoresis and Western blot. The amplified N genes were 1 176 bp in length and the deduced N proteins were 391 amino acids in length. The nucleotide identities of N genes among these seven strains were 85.4%-99.7% and the de-duced amino acid similarities were 95.4%-100%. The recombinant plasmid pET30a-N9968 had correct open reading frame confirmed by dual-enzyme digestion and sequence analysis. The fusion protein 6 x HisN was produced after inducing by 1 mmol/L IPTG at 37 degrees C. A unique protein band with molecular weight 49 kD was characterized by SDS-PAGE and purified by Ni2+ affinity chromatography column. Most of the target protein existed in inclusion body. Western blot analysis showed that the target protein had specific binding reaction to specific monoclonal antibody and human sera, indicating that the expressed protein is of specific antigenicity.
Base Sequence ; Child ; Escherichia coli ; genetics ; Humans ; Nucleocapsid Proteins ; genetics ; immunology ; Recombinant Proteins ; biosynthesis ; Respiratory Syncytial Virus, Human ; genetics ; Reverse Transcriptase Polymerase Chain Reaction

Severe fever with thrombocytopenia syndrome virus (SFTSV), a member of the Phlebovirus genus from the Bunyaviridae family endemic to China, is the causative agent of life-threatening severe fever with thrombocytopenia syndrome (SFTS), which features high fever and hemorrhage. Similar to other negative-sense RNA viruses, SFTSV encodes a nucleocapsid protein (NP) that is essential for viral replication. NP facilitates viral RNA encapsidation and is responsible for the formation of ribonucleoprotein complex. However, recent studies have indicated that NP from Phlebovirus members behaves in inhomogeneous oligomerization states. In the present study, we report the crystal structure of SFTSV NP at 2.8 Å resolution and demonstrate the mechanism by which it processes a ringshaped hexameric form to accomplish RNA encapsidation. Key residues essential for oligomerization are identified through mutational analysis and identified to have a significant impact on RNA binding, which suggests that correct formation of highly ordered oligomers is a critical step in RNA encapsidation. The findings of this work provide new insights into the discovery of new antiviral reagents for Phlebovirus infection.
Binding Sites ; Crystallography, X-Ray ; Mutation ; Nucleocapsid Proteins ; chemistry ; genetics ; metabolism ; Phlebovirus ; metabolism ; Protein Binding ; Protein Multimerization ; Protein Structure, Quaternary ; RNA, Viral ; metabolism ; Recombinant Proteins ; biosynthesis ; chemistry ; genetics