Effects of signal peptide on secretory expression of SARS-CoV-2 S1,RBD and RBD dimer proteins in Expisf9 insect cells / 中国生物制品学杂志

@#Objective To compare the effects of different signal peptides on the secretion and expression of SARS-CoV-2S1,receptor binding domain(RBD) and RBD dimer proteins in Expisf9 insect cells.Methods The gene sequences of three proteins,SARS-CoV-2 S1(M1-E661),RBD(R319-P545) and RBD dimer(R319-K537 tandem),were selected and divided into 25 groups according to the different N-terminal signal peptide sequences(Endo,honeybee melittin(HBM),GP64,GP67,chitinase(Chi) and HIV-ENV) and C-terminal label sequences.25 recombinant baculoviruses were constructed by Bac-to-Bac system,and 25 groups of tertiary strain banks were prepared.B2 and C4 viruses were inoculated to logarithmic prestage cells(2.8 × 10~6 cells/mL) and logarithmic metaphase cells(1.2 × 10~7 cells/mL),respectively.The viruses of each group were cultured to 100 mL(500 mL shaker) for protein expression,and samples were taken for SDSPAGE electrophoresis,Western-blot and ELISA detection.Two groups with higher expression levels of S1,RBD and RBD dimer proteins were selected for repeated verification.Results When B2 and C4 were inoculated to high cell density,the secretion expression level showed no increase,while there were significant difference between 4 and 5 d after inoculation.The expression level of A7(Endo-S1-tag) was significantly lower than that of A9(HIV-ENV-S1-tag),the expression level of A4(Gp67-S1-tag) was the highest,and the secreted expression level of A1(Endo-Endo-Sl-tag) was significantly lower than that of A7(Endo-S1-tag).The secretion and expression of B6(HIV-ENV-RBD-tag) was signifi-cantly higher than that of B4(Gp67-RBD-tag) and other signal peptide groups,and C4(Gp67-RBD-dimer-tag) expression was significantly higher than that of C3(Gp64-RBD-dimer-tag).Two groups with high expression of each protein were selected separately for repeated verification(A4,A9;B4,B6;C3,C4) and the results showed that A4,B6 and C4 had the highest secretion expression levels.Conclusion The signal peptide for the highest secretion expression of S1 and RBD dimer proteins is the same,which is GP67 signal peptide,while the most suitable signal peptide for RBD protein is HIV-ENV,indicating that the N-terminal sequence can affect protein secretion,signal peptide sequence is universal to a certain extent,but is also related to the target protein sequence to be expressed.

Trends of humoral immune responses to heterologous antigenic exposure due to vaccination & omicron SARS-CoV-2 infection: Implications for boosting

Background & objectives: Vaccination and natural infection can both augment the immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but how omicron infection has affected the vaccine-induced and hybrid immunity is not well studied in Indian population. The present study was aimed to assess the durability and change in responses of humoral immunity with age, prior natural infection, vaccine type and duration with a minimum gap of six months post-two doses with either ChAdOx1 nCov-19 or BBV152 prior- and post-emergence of the omicron variant. Methods: A total of 1300 participants were included in this observational study between November 2021 and May 2022. Participants had completed at least six months after vaccination (2 doses) with either ChAdOx1 nCoV-19 or an inactivated whole virus vaccine BBV152. They were grouped according to their age (? or ?60 yr) and prior exposure of SARS-CoV-2 infection. Five hundred and sixteen of these participants were followed up after emergence of the Omicron variant. The main outcome was durability and augmentation of the humoral immune response as determined by anti-receptor-binding domain (RBD) immunoglobulin G (IgG) concentrations, anti-nucleocapsid antibodies and anti-omicron RBD antibodies. Live virus neutralization assay was conducted for neutralizing antibodies against four variants – ancestral, delta and omicron and omicron sublineage BA.5. Results: Before the omicron surge, serum anti-RBD IgG antibodies were detected in 87 per cent participants after a median gap of eight months from the second vaccine dose, with a median titre of 114 [interquartile range (IQR) 32, 302] BAU/ml. The levels increased to 594 (252, 1230) BAU/ml post- omicron surge (P<0.001) with 97 per cent participants having detectable antibodies, although only 40 had symptomatic infection during the omicron surge irrespective of vaccine type and previous history of infection. Those with prior natural infection and vaccination had higher anti-RBD IgG titre at baseline, which increased further [352 (IQR 131, 869) to 816 (IQR 383, 2001) BAU/ml] (P<0.001). The antibody levels remained elevated after a mean time gap of 10 months, although there was a decline of 41 per cent. The geometric mean titre was 452.54, 172.80, 83.1 and 76.99 against the ancestral, delta, omicron and omicron BA.5 variants in the live virus neutralization assay. Interpretation & conclusions: Anti-RBD IgG antibodies were detected in 85 per cent of participants after a median gap of eight months following the second vaccine dose. Omicron infection probably resulted in a substantial proportion of asymptomatic infection in the first four months in our study population and boosted the vaccine-induced humoral immune response, which declined but still remained durable over 10 months

In vitro immunogenic profile of recombinant SARS-CoV2 S1-RBD peptide in murine macrophage and microglial cells

BACKGROUND The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants can infect common mice inducing significant pathological lung lesions and inflammatory responses. This substantially mimics coronavirus disease 19 (COVID-19) infection and pathogenesis in humans. OBJECTIVES To characterise the effects of recombinant SARS-CoV-2 S1 receptor-binding domain (RBD) peptide in murine macrophage and microglial cells' immune activation compared with classical PAMPs in vitro. METHODS Murine RAW 264.7 macrophages and BV2 microglial cells were exposed to increasing concentrations of the RBD peptide (0.01, 0.05, and 0.1 µg/mL), Lipopolysaccharide (LPS) and Poly(I:C) and evaluated after two and 24 h for significant markers of macrophage activation. We determined the effects of RBD peptide on cell viability, cleaved caspase 3 expressions, and nuclear morphometry analysis. FINDINGS In RAW cells, RBD peptide was cytotoxic, but not for BV2 cells. RAW cells presented increased arginase activity and IL-10 production; however, BV2 cells expressed iNOS and IL-6 after RBD peptide exposure. In addition, RAW cells increased cleaved-caspase-3, apoptosis, and mitotic catastrophe after RBD peptide stimulation but not BV2 cells. CONCLUSION RBD peptide exposure has different effects depending on the cell line, exposure time, and concentration. This study brings new evidence about the immunogenic profile of RBD in macrophage and microglial cells, advancing the understanding of SARS-Cov2 immuno- and neuropathology.

Construction of SARS-CoV-2 receptor binding domain molecular probe and its application in the isolation of neutralizing antibodies / 中国热带医学

@#Abstract: Objective　To construct SARS-CoV-2 receptor binding domain molecular probe for monoclonal memory B cell sorting and obtain RBD specific neutralizing antibodies from peripheral blood mononuclear cells (PBMCs) of COVID-19 convalescents by single-cell sorting. Methods　The SARS-CoV-2 RBD sequence was downloaded from GenBank, and the Avi tag and 6-histidine tags were added at the C-terminal. After codon optimization, it was chemically synthesized, cloned into the pDRVI1.0 vector, expressed after transfection of 293F cells, and biotinylated consequently. RBD-specific B cells were sorted out with this probe1 from the PBMCs of convalescents recovered from COVID-19. After B cells were lysed, the variable regions of heavy chain and light chain were amplified, cloned into the antibody expression vector, and transfected into 293F cells to express the antibody. Then the antibody was purified from the supernatant using protein A column and SARS-CoV-2 pseudovirus was used to test their neutralizing activity. Results　RBD-Avi probe was produced and successfully biotinylated sequentially with an efficiency of 30%-50%. Western blot analysis revealed that the biotinylated probe was recognized by the antibodies purified from COVID-19 convalescent plasma. Using this probe, 7 and 16 RBD-specific memory B cells were successfully isolated from the PBMCs of two convalescent individuals, accounting for 0.24% and 0.17% of the total cell population, respectively. After amplifying the variable regions of antibody heavy and light chains from the lysed B cells, 7 and 12 pairs of antibody heavy-light chains were obtained. A total of 16 antibodies were expressed in the convalescent individuals, and most of the purified antibodies showed neutralizing activity against the pseudovirus, with IC50 values of 6 antibodies below 1 μg/mL. The IC50 values of XJ-A9 and SCF-F1 against the wild-type pseudovirus were 0.07 μg/mL and 0.35 μg/mL, respectively. Conclusion　The SARS-CoV-2 RBD molecular probe constructed in this study has good antigenicity, and the isolated antibodies present neutralizing activity against wild-type SARS-CoV-2 pseudovirus.

Construction and identification of recombinant adenovirus expressing S protein receptor binding domain and N protein of SARS-CoV-2 Delta variant / 中国生物制品学杂志

@#ObjectiveTo construct and identify a recombinant adenovirus expressing S protein receptor binding domain(RBD)and N protein of severe acute respiratory symptom coronavirus 2(SARS-CoV-2)Delta variant.MethodsThe RBD and N gene fragments of SARS-CoV-2 were cloned into pcDNA3.0BA vector respectively to construct recombinant plasmid pcDNA3.0BA-RBD-N. The RBD-CMV-N fragment was amplified by PCR and inserted into shuttle vector pShuttle-CMV. The shuttle plasmid pShuttle-RBD-N was then homologously recombined with pAdeasy-1 to obtain recombinant plasmid pAdeasy-1-RBD-N,which was transfected into HEK293 cells for recombinant adenovirus Ad-RBD-N packaging. The transcription of RBD and N genes of recombinant adenovirus in HEK293 cells was detected by RT-PCR,while the expre-ssion of RBD and N proteins by Western blot and immunofluorescence assay. 12 female BALB/c mice were immunized with Ad-RBD-N by intramuscular injection at a dose of 5 × 109copies per mouse. Blood samples were collected 14 d after immunization,and the serum antibody titers were measured by ELISA.ResultsThe RBD and N genes of recombinant adenovirus were transcribed normally in HEK293 cells,and the RBD and N proteins were expressed normally in MA104 cells. Mice immunized with the recombinant adenovirus produced specific IgG antibodies against RBD and N proteins.ConclusionThe recombinant adenovirus expressing S protein RBD and N protein of SARS-CoV-2 Delta variant was succe-ssfully constructed,which laid a foundation of the follow-up research on Delta variant vaccines.

Screening and identification of single-chain fragment variable against the receptor-binding domain of spike protein of SARS-CoV-2 / 中国生物制品学杂志

@#Objective To construct a single-chain fragment variable(scFv)phage display library against receptor-binding domain(RBD)of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)spike protein(S)to screen specific scFv and identify the function.Methods m RNA was extracted from spleen cells of mice immunized with RBD protein and reversely transcribed into c DNA,with which as template,genes of the hight chain fragment of variable(VH)and light chain fragment of variable(VL)of scFv were amplified and then assembled into scFv gene fragment through splicing overlap extension PCR(SOE-PCR).The scFv gene fragment was inserted to phage vector to construct scFv phage display library.After four rounds of biopanning,the scFv gene with strong binding ability to RBD was screened and expressed recombinantly,purified and identified for biological activity.Results The constructed scFv phage library showed a titer of 6.0×10(11)pfu/m L.After four rounds of biopanning,four scFv strains with strong binding to RBD were selected,namely scFv11,scFv12,scFv25and scFv28.scFv was mainly expressed in the form of inclusion body with a relative molecular mass of about 27 000,a concentration of 2.4 mg/m L and a purity of about 90%,which bound specifically to mouse monoclonal antibody against His labeled by HRP after purification.All four scFv strains bound specifically to RBD recombinant protein,among which the other 3 scFv strains bound to the S protein of wild type and multiple mutant strains except scFv28.All four strains showed dose-dependent interaction with RBD,with affinity dynamic fitting dissociation constants(K_Ds)8.9,5.92,10.67and 2.36 nmol/L,and steady-state fitting dissociation constants(K_Ds)of 5.3,6.5,8.7 and 5.8 nmol/L,respectively.scFv11,scFv12 and scFv25 simultaneously identified three independent RBD polypeptides,including RBD2(S(11)pfu/m L.After four rounds of biopanning,four scFv strains with strong binding to RBD were selected,namely scFv11,scFv12,scFv25and scFv28.scFv was mainly expressed in the form of inclusion body with a relative molecular mass of about 27 000,a concentration of 2.4 mg/m L and a purity of about 90%,which bound specifically to mouse monoclonal antibody against His labeled by HRP after purification.All four scFv strains bound specifically to RBD recombinant protein,among which the other 3 scFv strains bound to the S protein of wild type and multiple mutant strains except scFv28.All four strains showed dose-dependent interaction with RBD,with affinity dynamic fitting dissociation constants(K_Ds)8.9,5.92,10.67and 2.36 nmol/L,and steady-state fitting dissociation constants(K_Ds)of 5.3,6.5,8.7 and 5.8 nmol/L,respectively.scFv11,scFv12 and scFv25 simultaneously identified three independent RBD polypeptides,including RBD2(S(334～353)),RBD9(S(334～353)),RBD9(S(439～458))and RBD13(S(439～458))and RBD13(S(499～518)).Homologous model of scFv constructed by online server SWISS-MODEL showed a good quality and was used for molecular docking.The interface at which scFv11 interacted with RBD only partially coincided with the interaction interface of human angiotensin converting enzyme 2(ACE2)and RBD,and the interaction interfaces of scFv12 and scFv25 with RBD were quite different from that of ACE2.Conclusion In this study,scFv specifically bound to SARS-Co V-2 RBD was screened and prepared through constructing scFv phage library against SARS-CoV-2 RBD,which provided experimental basis for further development of anti-SARS-CoV-2 drugs and detection reagents.

A trimeric RBD protein as a booster vaccine enhanced the humoral response and broad neutralization against SARS-CoV-2 in mice / 中华微生物学和免疫学杂志

Objective:To investigate the efficacy of a SARS-CoV-2 recombinant protein vaccine as a booster dose.Methods:A new immunogen, namely RBD-sc-trimer, was designed by tandem repeating of single receptor binding domain (RBD) of SARS-CoV-2 spike (S) protein to mimic the trimeric form of RBD presented by the virus. The RBD-sc-trimer protein was expressed as a His-tagged fusion protein using a baculovirus expression system and purified by nickel affinity column. The purified protein was identified by Western blot. Its in vitro binding activity to human angiotensin converting enzyme 2 (hACE2) was analyzed by ELISA. The immunogenicity of RBD-sc-trimer as well as RBD proteins of other forms including RBD dimer (RBD-Fc), RBD monomer (RBD) and S protein trimer (S trimer) as a booster dose was evaluated in BALB/c mice. Results:In terms of both binding and neutralizing antibodies against SARS-CoV-2, RBD-sc-trimer showed an immunogenicity that was superior to that of RBD-Fc and RBD and close to the level of S trimer. The antibody response induced by RBD-sc-trimer was characterized as Th1-biased. Moreover, it displayed a stronger cross-neutralization activity against SARS-CoV-2 Beta, Delta and Omicron variants. The titer of neutralizing antibody against Omicron induced by RBD-sc-trimer only decreased by 9.1 folds relative to the prototype strain, while the antibody response induced by RBD-Fc and S trimer decreased by 68.4 and 70.8 folds, respectively.Conclusions:The recombinant protein, RBD-sc-trimer, which was capable of eliciting stronger humoral response in mice as a booster dose and showed the superiority in raising cross-reactive antibodies against SARS-CoV-2 variants over non-trimeric RBD forms, should be considered as an optimal immunogen for the development of more effective SARS-CoV-2 vaccines.

Optimization of SARS-CoV-2 spike protein receptor binding domain expression in Pichia pastoris and evaluation of its immunogenicity / 中华微生物学和免疫学杂志

Objective:To effectively express the receptor binding domain (RBD) of SARS-CoV-2 spike protein in Pichia pastoris and to evaluate its immunogenicity. Methods:The gene encoding the RBD protein was synthesized and cloned into the pPICZαA plasmid. After linearization, the plasmid was transferred and integrated into the genome of Pichia pastoris. The expressed RBD protein in culture supernatant was analyzed by Western blot and Biolayer interferometry. After screening, a single clone expressing the RBD protein was selected. The high-level expression of RBD protein was achieved by optimizing the fermentation process, including the salt concentration adjusting of the medium and induction condition optimization (pH, temperature and duration). The immunogenicity of the expressed RBD protein was evaluated in a mouse model. Results:A single clone with a high expression level of RBD protein was obtained and named RBD-X33. The expression level of RBD protein in the fermentation supernatant reached up to 240 mg/L after optimization of the induction condition (HBSM medium, pH=6.5±0.3, 22℃ and 120 h). In the mouse experiment, the recombinant RBD protein was formulated with Alum+ CpG dual adjuvant and injected into mice. The binding IgG antibody levels were up to 2.7×10 6 tested by ELISA and the neutralizing antibody levels were up to 726.8 tested by live virus neutralizing antibody assay (prototype). Conclusions:The RBD protein could be efficiently expressed in Pichia pastoris and induce stronger immune response in animals. This study suggested that the recombinant SARS-CoV-2 RBD protein expressed in Pichia pastoris could serve as a candidate antigen in the development of SARS-CoV-2 vaccine.

Serological evaluation of immune effect of inactivated COVID-19 vaccine in adult population in Deqing County， Huzhou City， Zhejiang Province / 上海预防医学

ObjectiveTo investigate the specific anti-SARS-CoV-2 antibody in adults and above after initial vaccination with inactivated COVID-19 vaccine， and determine the influencing factors. MethodsIn this study， residents aged 18 and above who had completed two doses of inactivated COVID-19 vaccine in Deqing County， Huzhou City， Zhejiang Province were included. Information such as gender， age， type of vaccine and vaccination time were collected， and serum specimens were sampled. Anti-SARS-CoV-2 receptor binding domain （RBD） antibody was quantitatively examined by enzyma-linked immunosorbent assay （ELISA） and influencing factors were determined. ResultsThe median concentration of anti-SARS-CoV-2 IgG antibody in the residents vaccinated with an inactivated booster vaccine was higher than that in those vaccinated with only two doses of COVID-19 vaccine or single dose （P<0.05）. The median concentration of IgG antibody in males was 9.73 （4.01‒23.70） RU‧mL-1， lower than 17.76 （7.07‒49.23） RU‧mL-1 in females （P<0.05）. The median concentration in the residents vaccinated with BBIBP-CorV （Sinopharm） was 6.53 （0.97‒13.69） RU‧mL-1， which was lower than that in those vaccinated with CoronaVac （Sinovac） that was 17.29 （8.54‒43.73） RU‧mL-1 （P<0.05）. The median concentration in those with BBIBP-CorV was also lower than 12 （5.45‒40.06） RU‧mL-1 in those with heterologous booster vaccine （P<0.05）. The median concentration was 9.73 （3.83‒23.63） RU‧mL-1 in the residents with an interval of more than 6 months from the second dose， which was lower than 14.66 （6.36‒35.98） RU‧mL-1 in those with an interval of 3‒6 months （P<0.05）. Moreover， immune effect was better in females （χ²=16.464， P<0.05）， 18‒45 years（χ²=7.158， P<0.05）， and those vaccinated with CornaVac （χ²=49.637， P<0.05）， while decreased in those with an interval of more than 6 months from the second dose （χ²=8.447， P<0.05）. ConclusionGender， age， and type of vaccine may affect the effect of immunization. The COVID-19 vaccination shows an acceptable immunogenicity in adults； however， it declines in 6 months after vaccination. It warrants strengthening the booster vaccination to maintain the immune response.

Establishment and evaluation of receptor binding domain (RBD)-based ELISA for Middle East respiratory syndrome coronavirus (MERS-CoV) antibody detection / 中华微生物学和免疫学杂志

Objective@#To establish an indirect enzyme-linked immunosorbent assay (ELISA)and to compare the efficiency of receptor binding domain (RBD) proteins in different forms for Middle East respiratory syndrome coronavirus (MERS-CoV) antibody detection.@*Methods@#The monomeric and trimeric forms of MERS-CoV RBD were expressed in Bac-insect cells, 293T cells and ExpiCHO-S™ expression system and then purified. The purified RBD proteins were identified with native gel electrophoresis and Western blot. Then, an equal amount of each RBD protein was used as coating antigen to establish an ELISA for detecting MERS-CoV IgG titer. For comparison, the newly developed ELISA and the commercial MERS-CoV IgG antibody detection kit (Euroimmune with S1 as the coating antigen) were used to measure the MERS-CoV antibody reference panel supplied by World Health Organization (WHO).@*Results@#The purified monomeric and trimeric MERS-CoV RBD were successfully prepared using 293T cells and ExpiCHO-S™ system. RBD antigens of different forms and from different systems could recognize MERS-CoV specific antibody without having any cross reaction with the sera from healthy adults. The in-house RBD-based ELISA had good detection consistency with the Euroimmune commercial kit. The positive samples showed higher and more concentrated values based on the RBD trimer than the monomer.@*Conclusions@#Novel indirect ELISA methods based on the monomeric and trimeric forms of RBD protein were established. The trimetric form-based ELISA achieved higher detection efficiency than the one using the monomer antigen, suggesting that it could be uses as a competent alternative to the commercial kit.

Establishment and evaluation of receptor binding domain (RBD)-based ELISA for Middle East re-spiratory syndrome coronavirus (MERS-CoV) antibody detection / 中华微生物学和免疫学杂志

Objective To establish an indirect enzyme-linked immunosorbent assay (ELISA)and to compare the efficiency of receptor binding domain (RBD) proteins in different forms for Middle East re-spiratory syndrome coronavirus (MERS-CoV) antibody detection. Methods The monomeric and trimeric forms of MERS-CoV RBD were expressed in Bac-insect cells, 293T cells and ExpiCHO-STM expression sys-tem and then purified. The purified RBD proteins were identified with native gel electrophoresis and Western blot. Then, an equal amount of each RBD protein was used as coating antigen to establish an ELISA for de-tecting MERS-CoV IgG titer. For comparison, the newly developed ELISA and the commercial MERS-CoV IgG antibody detection kit (Euroimmune with S1 as the coating antigen) were used to measure the MERS-CoV antibody reference panel supplied by World Health Organization (WHO). Results The purified mon-omeric and trimeric MERS-CoV RBD were successfully prepared using 293T cells and ExpiCHO-STM system. RBD antigens of different forms and from different systems could recognize MERS-CoV specific antibody without having any cross reaction with the sera from healthy adults. The in-house RBD-based ELISA had good detection consistency with the Euroimmune commercial kit. The positive samples showed higher and more concentrated values based on the RBD trimer than the monomer. Conclusions Novel indirect ELISA methods based on the monomeric and trimeric forms of RBD protein were established. The trimetric form-based ELISA achieved higher detection efficiency than the one using the monomer antigen, suggesting that it could be uses as a competent alternative to the commercial kit.

Prokaryotic expression and characterization of receptor binding domain protein of the Middle East respiratory syndrome coronavirus / 中华微生物学和免疫学杂志

Objective To express the receptor binding domain (RBD) protein of the Middle East respiratory syndrome coronavirus (MERS-CoV) and to characterize the antigenicity of the purified recombi-nant protein. Methods The codon-optimized gene encoding the RBD protein of MERS-CoV was synthesized and then cloned into the pET30a ( +) vector to construct the recombinant expression plasmid. The trans-formed E. coli BL21 (DE3) strains carrying expression plasmid were induced by IPTG under different condi-tions. The expressed products were purified by using nickel affinity chromatography and further analyzed by SDS-PAGE and Western blot assay. Indirect ELISA was performed to analyze the antigenicity and specificity of RBD proteins expressed in prokaryotic expression systems in human serological test. Results The recom-binant RBD proteins were mainly expressed as conclusion body in an optimal induction condition of 37℃ and 0. 5 mmol/ L IPTG for 4 h. The high purified recombinant RBD proteins were obtained through denaturation and renaturation with a relative molecular mass of about 29×103 . Results of the Western blot assay showed that the recombinant RBD proteins could have specific reaction with the serum samples collected form mice with MERS-CoV infection. Indirect ELISA revealed that the RBD proteins expressed in the prokaryotic ex-pression system showed better sensitivity and specificity in the detection of antibodies against MERS-CoV in human serum samples. Conclusion This study reported the prokaryotic expression and purification of RBD protein of MERS-CoV for the first time, which might pave the way for further investigation on immunological detection of MERS-CoV and development of vaccines against MERS-CoV infection.

Screening of mouse-derived monoclonal antibodies against the receptor binding domain of Middle East respiratory syndrome coronavirus (MERS-CoV) spike protein / 中华微生物学和免疫学杂志

Objective To prepare and screen out monoclonal antibodies against the receptor bind-ing domain (RBD) of Middle East respiratory syndrome coronavirus ( MERS-CoV) spike ( S) protein in mice. Methods The RBD of MERS-CoV S protein expressed in the insect-baculovirus system was purified and then used to immunize the female BALB/ c mice. The spleen cells collected from the mice were fused with myeloma Sp2 / 0 cells. The positive hybridoma cells were obtained by using limited dilution method. Enzyme-linked immunosorbent assay ( ELISA), Western blot assay and neutralization test based on the MERS-CoV pseudovirus were performed for further screening and identification. Results Twelve strains of hybridoma cells that produced the monoclonal antibodies against RBD of MERS-CoV S protein were screened out. All of the 12 monoclonal antibodies (McAbs) could have specific reaction with the RBD of MERS-CoV S protein as indicated by the results of ELISA. Of the 12 McAbs, two were identified as the immunoglobulin M (IgM) isotype and the rest were IgG1 isotype by using double antibodies sandwich ELISA. Four McAbs including 1F1, 2E4, 3C3 and 3E6 were identified as having neutralizing activity by the neutralization test based on MERS-CoV pseudovirus. Results of the Western blot assay showed that the four McAbs (1F1, 2E4, 3C3 and 3E6) could have specific reaction with the RBD of MERS-CoV S protein, but no cross-reac-tion with that of SARS-CoV S protein. Conclusion Twelve mouse-derived McAbs against the RBD of MERS-CoV S protein were obtained. The prepared hybridoma cells showed the characteristics of high speci-ficity and stability in antibody secretion. Four out of the 12 McAbs were proved to have neutralizing activity.

Characterization of the Receptor-binding Domain of Ebola Glycoprotein in Viral Entry / 中国病毒学·英文版

Ebola virus infection causes severe hemorrhagic fever in human and non-human primates with high mortality.Viral entry/infection is initiated by binding of glycoprotein GP protein on Ebola virion to host cells,followed by fusion of virus-cell membrane also mediated by GP.Using an human immunodeficiency virus (HIV)-based pseudotyping system,the roles of 41 Ebola GP1 residues in the receptor-binding domain in viral entry were studied by alanine scanning substitutions.We identified that four residues appear to be involved in protein folding/structure and four residues are important for viral entry.An improved entry interference assay was developed and used to study the role of these residues that are important for viral entry.It was found that R64 and K95 are involved in receptor binding.In contrast,some residues such as I170 are important for viral entry,but do not play a major role in receptor binding as indicated by entry interference assay and/or protein binding data,suggesting that these residues are involved in post-binding steps of viral entry.Furthermore,our results also suggested that Ebola and Marburg viruses share a common cellular molecule for entry.

Construction and identification of bait expression vector of glucocorticoid receptor binding domain / 第三军医大学学报

Objective To construct the bait expression plasmid pGBKT7-GR of glucocorticoid receptor(GR)binding domain.Methods The fragments of GR binding domain was amplified by RT-PCR,and then was cloned into pMD18-T.After being verified by sequencing,it was subcloned into the bait expression vector pGBKT7.Then the bait vector pGBKT7-GR was transformed into AH109 yeast cells and the expression of the bait protein was analyzed by Western blot.Toxicity and self-activation of the bait protein were detected.Results GR binding domain was amplified and cloned into pMD18-T and pGBKT7 successfully.The bait vector was transformed into AH109 yeast cells successfully,without toxicity or self-activation.The expression of the bait protein was confirmed by Western blot.Conclusion The successful construction of bait expression vector of glucocorticoid receptor binding domain lays the foundation for constructing small molecule ligand yeast three-hybrid system.