Development of a Kit for Rapid Immunochromatographic Detection of Sacbrood Virus Infecting Apis cerana (AcSBV) Based on Polyclonal and Monoclonal Antibodies Raised against Recombinant VP1 and VP2 Expressed in Escherichia coli

A Korean isolate of the sacbrood virus infecting Apis cerana (AcSBV-Kor) is the most destructive honeybee virus, causing serious economic damage losses in Korean apiculture. To address this, here, we attempted to develop an assay for the rapid detection of AcSBV-Kor based on immunochromatographic detection of constituent viral proteins. Genes encoding VP1 and VP2 proteins of AcSBV-Kor were cloned into an expression vector (pET-28a) and expressed in Escherichia coli BL21(DE3). During purification, recombinant VP1 (rVP1) and VP2 (rVP2) proteins were found in the insoluble fraction, with a molecular size of 26.7 and 24.9 kDa, respectively. BALB/c mice immunized with the purified rVP1 and rVP2 produced polyclonal antibodies (pAbs) such as pAb-rVP1 and pAb-rVP2. Western blot analysis showed that pAb-rVP1 strongly reacted with the homologous rVP1 but weakly reacted with heterologous rVP2. However, pAb-rVP2 strongly reacted not only with the homologous rVP2 but also with the heterologous rVP1. Spleen cells of the immunized mice fused with SP2/0-Ag14 myeloma cells produced monoclonal antibodies (mAbs) such as mAb-rVP1-1 and mAb-rVP2-13. Western blot analysis indicated that pAb-rVP1, pAb-rVP2, mAb-rVP1-1, and mAb-rVP2-13 reacted with AcSBV-infected honeybees and larvae as well as the corresponding recombinant proteins. These antibodies were then used in the development of a rapid immunochromatography (IC) strip assay kit with colloidal gold coupled to pAb-rVP1 and pAb-rVP2 at the conjugate pad and mAb-rVP1-1 and mAb-rVP2-13 at the test line. One antibody pair, pAb-rVP1/mAb-VP1-1, showed positive reactivity as low as 1.38 × 10³ copies, while the other pair, pAb-rVP2/mAb-VP2-13, showed positive reactivity as low as 1.38 × 10⁴ copies. Therefore, the antibody pair pAb-rVP1/mAb-VP1-1 was selected as a final candidate for validation. To validate the detection of AcSBV, the IC strip tests were conducted with 50 positive and 50 negative samples and compared with real-time PCR tests. The results confirm that the developed IC assay is a sufficiently sensitive and specific detection method for user-friendly and rapid detection of AcSBV.

Establishment of a two-step purification scheme for tag-free recombinant Taiwan native norovirus P and VP1 proteins

The protruding (P) domain of the major capsid protein VP1 of norovirus (NoV) is the crucial element for immune recognition and host receptor binding. The heterologous P protein expressed by Pichia pastoris self-assembles into P particles. However, tag-free NoV protein purification schemes have rarely been reported due to the low isoelectric point of NoV proteins, which leads to highly competitive binding between the target protein and yeast host cell proteins at alkaline pH. In this study, a two-step purification scheme based on surface histidines and the charge on the NoV GII.4 strain P protein was developed. Using HisTrap and ion exchange chromatography, the P protein was directly purified, with a recovery of 28.1% and purity of 82.1%. Similarly, the NoV capsid protein VP1 was also purified using HisTrap and gel filtration chromatography based on native surface histidines and self-assembly ability, with 20% recovery and over 90% purity. Dynamic light scattering and transmission electron microscopy analyses of the purified NoV P revealed that most of these small P particles were triangle-, square- and ring-shaped, with a diameter of approximately 14 nm, and that the purified NoV VP1 self-assembles into particles with a diameter of approximately 47 nm. Both the purified NoV P and VP1 particles retained human histo-blood group antigen-binding ability, as evidenced by a saliva-binding assay.

Comparison of homologous and heterologous prime-boost immunizations combining MVA-vectored and plant-derived VP2 as a strategy against IBDV

Different immunogens such as subunit, DNA or live viral-vectored vaccines against Infectious Bursal Disease virus (IBDV) have been evaluated in the last years. However, the heterologous prime-boost approach using recombinant modified vaccinia Ankara virus (rMVA), which has shown promising results in both mammals and chickens, has not been tried against this pathogen yet. IBD is a highly contagious and immunosuppressive disease of poultry that affects mainly young chicks. It is caused by IBDV, a double-stranded RNA virus carrying its main antigenic epitopes on the capsid protein VP2. Our objective was to evaluate the immune response elicited by two heterologous prime-boost schemes combining an rMVA carrying the VP2 mature gene (rVP2) and a recombinant VP2 protein produced in Nicotiana benthamiana (pVP2), and to compare them with the performance of the homologous pVP2-pVP2 scheme usually used in our laboratory. The SPF chickens immunized with the three evaluated schemes elicited significantly higher anti-VP2 antibody titers (p<0.001) and seroneutralizing titers (p<0.05) and had less T-cell infiltration (p<0.001), histological damage (p<0.001) and IBDV particles (p<0.001) in their bursae of Fabricius when compared with control groups. No significant differences were found between both heterologous schemes and the homologous one. However, the rVP2-pVP2 scheme showed significantly higher anti-VP2 antibody titers than pVP2-rVP2 and a similar tendency was found in the seroneutralization assay. Conversely, pVP2-rVP2 had the best performance when evaluated through bursal parameters despite having a less potent humoral immune response. These findings suggest that the order in which rVP2 and pVP2 are combined can influence the immune response obtained. Besides, the lack of a strong humoral immune response did not lessen the ability to protect from IBDV challenge. Therefore, further research is needed to evaluate the mechanisms by which these immunogens are working in order to define the combination that performs better against IBDV.

New approach for identification of bacteriophage virion structural proteins

The ability of the phage structural polypeptides to undergo post-translational modification makes the task of correlation of the primary nucleotide sequence data with the actual structural proteins of a virion extremely challenging. This study describes an alternative model approach based on two-stage chromatography for allocation of virion structural components and identification of their major polypeptides. Bacteriophage T4D, its amber mutant T4D23 (amH11) and its tail preparations were purified, concentrated and separated by ion exchange chromatograpgy based on fibrous DEAE-cellulose. The major tail fraction was then exposed to size-exclusion chromatography which enabled to separate tail components by size. This method proved itself as a highly efficient and gentle enough to save most of the biological material without changing the basic properties of the native phage. The result also shows that the accumulation of individual phage tails in the course of the amber mutant T4D23 (amH11) propagation on the permissive host Escherichia coli CR63 was resulted by changes in the conditions of reproduction. The ability of bacteriophages to form an excess of tails, capsids and other structures during reproduction on a non-traditional host provides an alternative way for obtaining highly concentrated preparations of virion components for further analysis of their major proteins and determination of the genes responsible for their synthesis.

Antiserum to the recombinant truncated VP22 protein of herpes simplex virus type 1 that also recognizes full-length VP22

The herpes simplex virus type 1 (HSV-1) tegument protein VP22 encoded by the UL49 gene is essential for HSV-1 infection. However, its precise functions in the virus life cycle are unknown. A relatively important tool for disclosing these functions is an antiserum specifically detecting VP22 in the infected cell. To this end, a recombinant truncated VP22 protein consisting of C-terminal 45 aa fused to EYFP (enhanced yellow fluorescent protein) and His-tag was expressed in Escherichia coli, purified by the Ni2+-NTA affinity chromatography, and used for the preparation of antiserum in rabbits. Western blot and immunofluorescence assay showed that this antiserum specifically detected purified truncated VP22 as well as full-length VP22 in the HSV-1 infected cells. These results indicate that the prepared antiserum could serve as a valuable tool for further studies of VP22 functions.

Baculovirus-expressed virus-like particles of Pea enation mosaic virus vary in size and encapsidate baculovirus mRNAs

Pea enation mosaic virus (PEMV: family Luteoviridae) is transmitted in a persistent, circulative manner by aphids. We inserted cDNAs encoding the structural proteins of PEMV, the coat protein (CP) and coat protein-read through domain (CPRT) into the genome of the baculovirus Autographa californica multiple nucleopolyhedrovirus with and without a histidine tag or an upstream Kozak consensus sequence. The Sf21 cell line provided the highest level of CP expression of the cell lines tested and resulted in production of virus-like particles (VLPs). The CPRT was not detected in recombinant baculovirus-infected cells by Western blot. Addition of a Kozak sequence increased the yield of baculovirus produced VLPs. Baculovirus-expressed VLPs purified on a nickel NTA column were of variable size (13-30 nm) and contained CP mRNA. The purified VLPs were also shown by RT-PCR to contain 70% of 154 baculovirus mRNAs, indicative of non-specific RNA encapsidation in the absence of viral RNA replication. When fed to the pea aphid, Acyrthosiphon pisum (Harris), the VLPs entered the aphid hemocoel, demonstrating that CPRT is not required for uptake of PEMV from the aphid gut. Baculovirus expression of PEMV VLPs provides a useful tool for future analysis of RNA encapsidation requirements and molecular aphid-virus interactions.

Detection of L1, infectious virions and anti-L1 antibody in domestic rabbits infected with cottontail rabbit papillomavirus

Shope papillomavirus or cottontail rabbit papillomavirus (CRPV) is one of the first small DNA tumour viruses to be characterized. Although the natural host for CRPV is the cottontail rabbit (Sylvilagus floridanus), CRPV can infect domestic laboratory rabbits (Oryctolagus cuniculus) and induce tumour outgrowth and cancer development. In previous studies, investigators attempted to passage CRPV in domestic rabbits, but achieved very limited success, leading to the suggestion that CRPV infection in domestic rabbits was abortive. The persistence of specific anti-L1 antibody in sera from rabbits infected with either virus or viral DNA led us to revisit the questions as to whether L1 and infectious CRPV can be produced in domestic rabbit tissues. We detected various levels of L1 protein in most papillomas from CRPV-infected rabbits using recently developed monoclonal antibodies. Sensitive in vitro infectivity assays additionally confirmed that extracts from these papillomas were infectious. These studies demonstrated that the CRPV/New Zealand White rabbit model could be used as an in vivo model to study natural virus infection and viral life cycle of CRPV and not be limited to studies on abortive infections.

Ion-exchange membrane chromatography method for rapid and efficient purification of recombinant baculovirus and baculovirus gp64 protein

Significant progress in the application of baculoviral vectors for gene delivery into mammalian cells calls for the development of powerful methods for virus purification and concentration. We report here a novel and efficient method based on membrane chromatography to prepare baculoviral stocks. On a strong cation-exchange membrane unit, baculovirus in insect cell culture supernatants was captured at a flow rate of 3 ml/min and efficiently eluted at the same flow rate with a physiological buffer containing 150 mM NaCl as a desorption reagent. The procedure allowed for a final recovery of 78% of infective viral particles from the original supernatant and 30-fold enrichment. The high purity of the viral preparation was demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Baculovirus gp64 proteins could be purified by the same method, indicating the importance of the protein in mediating the binding of baculovirus to the cation-exchange membrane. The method developed should be suitable for preparing baculoviral stocks, and probably other gp64-pseudotyped viral vectors, for gene therapy applications.

Identification of Trichoplusia ni ascovirus 2c virion structural proteins

Ascoviruses are a family of insect viruses with circular, double-stranded DNA genomes. With the sequencing of the Trichoplusia ni ascovirus 2c (TnAV-2c) genome, the virion structural proteins were identified by using tandem mass spectrometry. From at least eight protein bands visible on a Coomassie blue-stained gel of TnAV-2c virion proteins, seven bands generated protein sequences that matched predicted open reading frames (ORFs) in the genome, i.e. ORFs 2, 43, 115, 141, 142, 147 and 153. Among these ORFs, only ORF153, encoding the major capsid protein, has been characterized previously.

Development of a low-cost, insect larvae-derived recombinant subunit vaccine against RHDV

Vaccine antigens against rabbit hemorrhagic disease virus (RHDV) are currently derived from inactivated RHDV obtained from livers of experimentally infected rabbits. Several RHDV-derived recombinant immunogens have been reported. However, their application in vaccines has been restricted due to their high production costs. In this paper, we describe the development of an inexpensive, safe, stable vaccine antigen for RHDV. A baculovirus expressing a recombinant RHDV capsid protein (VP60r) was used to infect Trichoplusia ni insect larvae. It reached an expression efficiency of 12.5% of total soluble protein, i.e. approximately 2 mg of VP60r per larva. Preservation of the antigenicity and immunogenicity of the VP60r was confirmed by immunological and immunization experiments. Lyophilized crude larvae extracts, containing VP60r, were stable, at room temperature, for at least 800 days. In all cases, rabbits immunized with a single dose of VP60r by the intramuscular route were protected against RHDV challenge. Doses used were as low as 2 microg of VP60r in the presence of adjuvant or 100 microg without one. Orally administered VP60r in the absence of an adjuvant gave no protection. The potential costs of an RHDV vaccine made using this technology would be reduced considerably compared with producing the same protein in insect cells maintained by fermentation. In conclusion, the larva expression system may provide a broad-based strategy for production of recombinant subunit antigens (insectigens) for human or animal medicines, especially when production costs restrain their use.

In VitroExpression and Monoclonal Antibody of RNA-Dependent RNA Polymerase for Infectious Bursal Disease Virus

VP1, the RNA-dependent RNA polymerase of infectious bursal disease virus (IBDV), has been suggested to play an essential role in the replication and translation of viral RNAs. In this study, we first expressed the complete VP1 protein gene in Escherichia coli (E. coli), and then the produced polyclonal antibody and four monoclonal antibodies (mAbs) to recombinant VP1 protein (rVP1) were shown to bind the IBDV particles in chicken embryo fibroblast and Vero cells. The epitopic analysis showed that mAbs 1D4 and 3C7 recognized respectively two distinct antigenic epitopes on the rVP1 protein, but two pair of mAbs 1A2/2A12 and 1E1/1H3 potentially recognized another two topologically related epitopes. Immunocytochemical stainings showed that VP1 protein formed irregularly shaped particles in the cytoplasm of the IBDV-infected cells. These results demonstrated that the mAbs to rVP1 protein could bind the epitopes of IBDV particles, indicating that the rVP1 protein expressed in E. coli was suitable for producing the mAb to VP1 protein of IBDV, and that the cytoplasm could be the crucial site for viral genome replication of IBDV.

Localization studies of two white spot syndrome virus structural proteins VP51 and VP76

VP51 and VP76 are two structural proteins of white spot syndrome virus (WSSV). However, there is some controversy about their localization in the virion at present. In this study, we employ multiple approaches to reevaluate the location of VP51 and VP76. Firstly, we found VP51 and VP76 presence in viral nucleocapsids fraction by Western blotting. Secondly, after the high-salt treatment of nucleocapsids, VP51 and VP76 were still exclusively present in viral capsids by Western blotting and immunoelectron microscopy, suggesting two proteins are structural components of the viral capsid. To gather more evidence, we developed a method based on immunofluorescence flow cytometry. The results revealed that the mean fluorescence intensity of the viral capsids group was significantly higher than that of intact virions group after incubation with anti-VP51 or anti-VP76 serum and fluorescein isothiocyanate conjugated secondary antibody. All these results indicate that VP51 and VP76 are both capsid proteins of WSSV.

Purification of VP3 protein of infectious bursal disease virus using nickel ion-immobilized regenerated cellulose-based membranes

In this study, hexa-histidine tagged VP3 protein of infectious bursal disease virus (IBDV) was purified using immobilized metal ion affinity technique from the fermentation of Escherichia coli BL21 (DE3) containing a recombinant plasmid with a VP3 gene. The purification efficiencies of VP3 protein (TVP3 and DeltaTVP3) using Ni(2+)-NTA commercial agarose gels and Ni(2+)-IDA regenerated cellulose-based membranes at 4 degrees C were compared. A good washing condition for removing most impurity proteins was found as 20 mM NaH(2)PO(4), 500 mM NaCl, 40 mM imidazole, pH 7.8, whereas an efficient elution condition was 20 mM NaH(2)PO(4), 500 mM NaCl, 500 or 750 mM imidazole, pH 7.8. By applying these conditions to the flow experiments, similar recovery (86-88%) and purity (98-99%) for VP3 were obtained in both gel column (1 ml gel) and membrane cartridge (four membrane disks) under the flow rate of 1.7 ml/min for protein loading and 2.7 ml/min for protein elution. Regarding that the membrane process exhibited some advantages such as shorter residence time and lower cost, a better process efficiency in a large-scale system could be expected for the Ni(2+)-IDA membranes.

Severe acute respiratory syndrome coronavirus group-specific open reading frames encode nonessential functions for replication in cell cultures and mice

SARS coronavirus (SARS-CoV) encodes several unique group-specific open reading frames (ORFs) relative to other known coronaviruses. To determine the significance of the SARS-CoV group-specific ORFs in virus replication in vitro and in mice, we systematically deleted five of the eight group-specific ORFs, ORF3a, OF3b, ORF6, ORF7a, and ORF7b, and characterized recombinant virus replication and gene expression in vitro. Deletion of the group-specific ORFs of SARS-CoV, either alone or in various combinations, did not dramatically influence replication efficiency in cell culture or in the levels of viral RNA synthesis. The greatest reduction in virus growth was noted following ORF3a deletion. SARS-CoV spike (S) glycoprotein does not encode a rough endoplasmic reticulum (rER)/Golgi retention signal, and it has been suggested that ORF3a interacts with and targets S glycoprotein retention in the rER/Golgi apparatus. Deletion of ORF3a did not alter subcellular localization of the S glycoprotein from distinct punctuate localization in the rER/Golgi apparatus. These data suggest that ORF3a plays little role in the targeting of S localization in the rER/Golgi apparatus. In addition, insertion of the 29-bp deletion fusing ORF8a/b into the single ORF8, noted in early-stage SARS-CoV human and civet cat isolates, had little if any impact on in vitro growth or RNA synthesis. All recombinant viruses replicated to wild-type levels in the murine model, suggesting that either the group-specific ORFs play little role in in vivo replication efficiency or that the mouse model is not of sufficient quality for discerning the role of the group-specific ORFs in disease origin and development.

Characterization of different viruses infecting the marine harmful algal bloom species Phaeocystis globosa

Twelve lytic viruses (PgV) infecting the marine unicellular eukaryotic harmful algal bloom species Phaeocystis globosa were isolated from the southern North Sea in 2000-2001 and partially characterized. All PgV isolates shared common phenotypic features with other algal viruses belonging to the family Phycodnaviridae and could be categorized in four different groups. Two main groups (PgV Group I and II) were discriminated based on particle size (150 and 100 nm respectively), genome size (466 and 177 kb) and structural protein composition. The lytic cycle showed a latent period of 10 h for PgV Group I and latent periods of 12 h and 16 h for PgV Group IIA and IIB. Host specificity and temperature sensitivity finally defined a fourth group (PgV Group IIC). Our results imply that viral infection plays an important role not only in P. globosa dynamics but also in the diversity of both host and virus community.

Mutation of E1 glycoprotein of classical swine fever virus affects viral virulence in swine

Transposon linker insertion mutagenesis of a full-length infectious clone (IC) (pBIC) of the pathogenic classical swine fever virus (CSFV) strain Brescia was used to identify genetic determinants of CSFV virulence and host range. Here, we characterize a virus mutant, RB-C22v, possessing a 19-residue insertion at the carboxyl terminus of E1 glycoprotein. Although RB-C22v exhibited normal growth characteristics in primary porcine macrophage cell cultures, the major target cell of CSFV in vivo, it was markedly attenuated in swine. All RB-C22v-infected pigs survived infection remaining clinically normal in contrast to the 100% mortality observed for BICv-infected animals. Comparative pathogenesis studies demonstrated a delay in RB-C22v spread to, and decreased replication in the tonsils, a 10(2) to 10(7) log10 reduction in virus titers in lymphoid tissues and blood, and an overall delay in generalization of infection relative to BICv. Notably, RB-C22v-infected animals were protected from clinical disease when challenged with pathogenic BICv at 3, 5, 7, and 21 days post-RB-C22v inoculation. Viremia, viral replication in tissues, and oronasal shedding were reduced in animals challenged at 7 and 21 DPI. Notably BICv-specific RNA was not detected in tonsils of challenged animals. These results indicate that a carboxyl-terminal domain of E1 glycoprotein affects virulence of CSFV in swine, and they demonstrate that mutation of this domain provides the basis for a rationally designed and efficacious live-attenuated CSF vaccine.

Purification of capsid-like particles of infectious bursal disease virus (IBDV) VP2 expressed in E. coli with a metal-ion affinity membrane system

Protein VP2, matured from the polyprotein encoded by the genome of infectious bursal disease virus (IBDV) and the primary host-protective immunogen of this virus, together with its two N-terminal truncated mutants were cloned and expressed in Escherichia coli. To obtain pure recombinant proteins for the development of an efficient subunit vaccine against IBDV infection, these three proteins were fused with six additional histidine residues at their C-termini as a His-purification-tag. Following purification employing immobilized metal-ion (Ni2+) affinity chromatography (IMAC), a purification fold of approximately 104 was achieved. Electron microscopic observation also demonstrated that all three E. coli-derived proteins form the morphology of icosahedral particles of approximately 25 nm in diameter. To reduce the cost of resin used for IMAC, self-prepared immobilized metal-ion affinity membranes (IMAM), i.e., commercial, regenerated cellulose membrane modified with iminodiacetic acid and immobilized with nickel ions, was applied to purify particles formed by these three proteins. A 104-fold of purification efficiency was also achieved by this membrane, showing that under the same conditions the recovery and purification efficiency of IMAM are comparable with those of IMAC. The pure VP2-formed particles thus obtained, coupled with their uniform dimensions, not only facilitate a better understanding of the structural biology of these immunogenic particles but also help the development of improved vaccines against this avian virus.

High-level expression and immunogenic properties of the recombinant rabbit hemorrhagic disease virus VP60 capsid protein obtained in Pichia pastoris

The VP60 capsid protein from rabbit hemorrhagic disease virus (RHDV) (Spanish isolate AST/89) was cloned and expressed in Pichia pastoris. The transformed yeast was grown at high cell density and an expression level of about 1.5 g VP60L(-1) culture was obtained. The protein was detected associated with the cell debris fraction of the recombinant yeast after mechanical disruption. It was purified by a simple method and was obtained N-glycosylated with purity of approximately 70% as deduced from densitometry scan analysis. The recombinant product was antigenically similar to the native capsid protein as determined with polyclonal antibodies obtained from rabbits vaccinated with VP60 protein purified from native virus. The immunogenicity of VP60 protein purified from P. pastoris was demonstrated by ELISA in a vaccination experiment conducted with two groups of rabbits subcutaneously immunized. Animals vaccinated with VP60 in Freund's incomplete adjuvant developed a significant (p<0.01) virus-specific antibody response while the group injected with placebo remained seronegative. Preliminary results showed that the antigen administered within the cell debris fraction of the transformed yeast protected rabbits immunized by the oral route against an intramuscular challenge with 100 LD50 (16,000 hemagglutination units) of homologous virus.

Characterization of particles formed by the precursor protein VPX of infectious bursal disease virus in insect Hi-5 cells: implication on its proteolytic processing

The precursor (VPX) of host immunogen VP2 protein for infectious bursal disease virus (IBDV) was expressed in insect Sf9 and Hi-5 cells, and the types of particles generated as well as the immunogenicity induced by these particles were examined. Recombinant VPXH (rVPXH) protein, expressed in Hi-5 cells at an expression level 4x higher than in Sf9 cells, was efficiently processed by proteases to yield VP2-like proteins with corresponding molecular weight, a phenomenon not observed previously. At least three structures of particles were observed for VPXH and VP2-like proteins purified by immobilized metal-ion affinity chromatography (MAC). In addition to the two previously identified twisted tubular and isometric particle structures, there was a new one: icosahedral particles of approximately 25 nm in diameter. The purified particles were further separated by gel-filtration chromatography (GFC) linking with HPLC, which was able to resolve the isometric from icosahedral particles better than ultracentrifugation. Chromatographic results indicate that rVPXH protein mainly involved in the formation of the isometric particle structure and occasionally twisted tubular structure, and the icosahedral particles were formed by the degraded products of rVPXH (VP2-like proteins). Thus, by combining IMAC and GFC, it was shown that VPX was processed efficiently to yield VP2-like protein that could form small virus-like particles in Hi-5 cells. Finally, we demonstrated that virus-neutralizing antibodies were induced when susceptible chickens were vaccinated with the IMAC-purified rVPXH protein (40 microg per bird). This indicates that these particles are highly immunogenic and might serve as an alternative vaccine candidate for the development of IBDV subunit vaccine.

Severe acute respiratory syndrome coronavirus 3a protein is a viral structural protein

The present study showed the association of a severe acute respiratory syndrome coronavirus (SCoV) accessory protein, 3a, with plasma membrane and intracellular SCoV particles in infected cells. 3a protein appeared to undergo posttranslational modifications in infected cells and was incorporated into SCoV particles, establishing that 3a protein was a SCoV structural protein.

[Expression of capsid gene of Chinese isolate of rabbit hemorrhagic disease virus in Pichia pastoris]

The capsid protein (VP60) gene of RHDV was subcloned into the Pichia expressin vector pPICZ B to express the VP60 protein intracellularly. The recombinant plasmid was initially transformed into a E. coli strain TOP10 F'. After verification of the construct by sequencing, the recombinant plasmid was linearized by Sac I in the 5' AOX1 region and then transformed into Pichia pastoris strain GS115 using the Pichia EasyComp Kit. After selecting and verifing for the insertion of VP60 gene in the genome, two clones of Pichia transformants were select for expression test. The recombinant clones were first inoculate with BMGY in baffled flask at 28-30 degrees C in a shaking incubator (250-300 r/min) until culture reaches an OD600 = 2-6, then resuspend the cell pellet to an OD6oo of 1.0 in BMMY medium to induce expression for 5 days by methanol at a concentration of 0.5% in a 1 liter baffled flask covered with 2 layers of sterile gauze. Collect the cell pellets and break it by acid-washed 0.5 mm glass beads. The expression of recombinant Pichia strains was detected by SDS-PAGE and Western analysis with a polyclonal serum which showed a specific protein band of 60kD. Theses results indicates that the recombinant VP60 produced in Pichia was antigenically similar to the viral polypeptide. Electron microscopic observation of the recombinant Pichia-derived protein revealed the presence of virus-like particles similar in size and appearance to native virus capsids. In the haemagglutination test, the recombinant VLPs, like the native RHDV, also agglutinated human blood type O erythrocytes and could be inhibited by the anti-RHDV polyclonal serum.

Crystallization and preliminary X-ray analysis of gene product 44 from bacteriophage Mu

Bacteriophage Mu baseplate protein gene product 44 (gp44) is an essential protein required for the assembly of viable phages. To investigate the roles of gp44 in baseplate assembly and infection, gp44 was crystallized at pH 6.0 in the presence of 20% 2-methyl-2,4-pentanediol. The crystals belong to space group R3, with unit-cell parameters a = b = 127.47, c = 63.97 A. The crystals diffract X-rays to at least 2.1 A resolution and are stable in the X-ray beam and are therefore appropriate for structure determination. Native data have been collected to 2.1 A resolution using a DIP6040 image-plate system at beamline BL44XU at the SPring-8 facility in Japan.

The product of the bacteriophage lambda W gene: purification and properties

Gene W is one of the 10 genes that control the morphogenesis of the bacteriophage lambda head. The morpho genesis of the phage lambda head proceeds through the synthesis of an intermediate assembly called the prohead. This is an empty shell into which the bacteriophage DNA is introduced--packaged--by the phage enzyme DNA terminase. The product of W (gpW) acts after DNA packaging, but before the addition of another phage product, gene product FII, and before the addition of tails. The role of gpW is unknown. The structure of N- and C-tagged gpW has been previously determined by nuclear magnetic resonance (NMR) spectroscopy. Here we report some of the properties of the native protein. The purification of gpW to homogeneity, overproduced by a plasmid derivative, is described. To obtain large amounts of the protein, the ribosome-binding site had to be modified, showing that inefficient translation of the message is the main mechanism limiting W gene expression. The molecular weight of the protein is in close agreement to the value predicted from the DNA sequence of the gene, which suggests that it is not post-transcriptionally modified. It behaves as a monomer in solution. Radioactively labeled gpW is incorporated into phage particles in in vitro complementation, showing that gpW is a structural protein. The stage at which gpW functions and other circumstantial evidence support the idea that six molecules of gpW polymerize on the connector before the incorporation of six molecules of gpFII and before the tail attaches.

An assembly model of Rice dwarf virus particle

The Phytoreovirus rice dwarf virus (RDV) has a complex nucleocapsid architecture composed of multiple proteins and RNAs. However, specific RNA-protein and protein-protein interactions involved in virion packaging have not been entirely elucidated. In order to define mechanisms governing RDV particle assembly, interactions between individual components were analyzed both in vivo and in vitro. The P7 core protein binds specifically and with high affinity to all 12 genomic RDV dsRNAs. P1, a putative RNA polymerase, P5, a putative guanyltransferase and P7 are encapsidated within the virion and also bind viral transcripts based upon in vitro binding assays. P1, P5, P7 and genomic dsRNAs were lacking in empty particles purified from infected tissues that also yielded fractions containing intact, infectious particles. In addition, P7 forms complexes with P1 and P3, a core capsid protein, in viral particles. These results indicate the possibility that core proteins and dsRNAs interact as one unit suggesting a mechanism for assortment of viral RNAs and subsequent packaging into core particles.

Different contributions of the outer and inner R-core residues of lipopolysaccharide to the recognition by spike H and G proteins of bacteriophageφX174

The binding of spike H and G proteins of bacteriophage phiX174 with lipopolysaccharides (LPSs) were evaluated by a competitive enzyme-linked plate assay using the biotin-labeled LPS of Escherichia coli C, one of a host strain, and the non-labeled LPSs having different R-core polysaccharide lengths. H protein promptly decreased its affinity when some saccharide residues were truncated from the outer R-core. However, G protein showed significant affinity to the LPSs lacking all the residues of the outer R-core and some of the inner R-core. Thus, G protein rather than H protein well recognized the residues of the inner R-core of LPS.

[Over-expression in Escherichia coli and purification of nucleocaspid and membrane protein of SARS coronavirus]

Genes encoding nucleocaspid (N) and membrane (M) protein of SARS coronavirus were obtained by RT-PCR and were cloned into expression vector pET22b and pBV222. DNA sequencing showed that the genes cloned from a patient in Beijing were identical to the gene sequences from reported Toronto strain. The genes were over-expressed in E. coli either as inclusion body or as soluble form. The recombinant proteins were purified by ion-exchange, or ion-exchange followed by metal chelate affinity chromatography. The recombinant N protein was demonstrated highly antigenic and could be employed as antigen to detect SARS antibodies in ELISA system for SARS diagnosis.

P15 and P3, the tail completion proteins of bacteriophage T4, both form hexameric rings

Two proteins, gp15 and gp3 (gp for gene product), are required to complete the assembly of the T4 tail. gp15 forms the connector which enables the tail to bind to the head, whereas gp3 is involved in terminating the elongation of the tail tube. In this work, genes 15 and 3 were cloned and overexpressed, and the purified gene products were studied by analytical ultracentrifugation, electron microscopy, and circular dichroism. Determination of oligomerization state by sedimentation equilibrium revealed that both gp15 and gp3 are hexamers of the respective polypeptide chains. Electron microscopy of the negatively stained P15 and P3 (P denotes the oligomeric state of the gene product) revealed that both proteins form hexameric rings, the diameter of which is close to that of the tail tube. The differential roles between gp15 and gp3 upon completion of the tail are discussed.

Nucleotide sequence analysis of variable region of VP2 gene of two infectious bursal disease virus isolates from commercial poultry farms

Two infectious bursal disease virus (IBDV) isolates were obtained from commercial poultry farms with a history of severe outbreaks. A 474-bp product encompassing hypervariable region of IBDV VP2 gene was amplified by reverse transcription-polymerase chain reaction (RT-PCR). The nucleotide sequences of two isolates, VMB1 and VMB2, were determined and compared with those of twenty IBDV strains, including seven very virulent, four classical virulent, four classical attenuated, three antigenic variants and two avirulent serotype 2 strains. The two isolates showed a similarity of 96.5-98.4% with very virulent strains, 84.6-94.6% with classical virulent strains, 90.0-91.4% with classical attenuated strains, 83.0-91.9% with antigenic variants and 65.8-68.7% with avirulent strains. The deduced amino acid sequences of the two isolates showed amino acid substitutions of V256I, N279D, L294I and N299S, specific for very virulent strains. Phylogenetic analysis showed that the two isolates, along with a reported very virulent Indian strain, were closely related to European, Japanese and Chinese very virulent strains indicating their evolutionary origin.

Reconstitution of hepatitis C virus envelope glycoproteins into liposomes as a surrogate model to study virus attachment

The envelope glycoproteins, E1 and E2, of hepatitis C virus (HCV) assemble intracellularly to form a noncovalent heterodimer that is expected to be essential for viral assembly and entry. However, due to the lack of a cell culture system supporting efficient HCV replication, it is very difficult to obtain relevant information on the functions of this glycoprotein oligomer. To get better insights into its biological and biochemical properties, HCV envelope glycoprotein heterodimer expressed by a vaccinia virus recombinant was purified by immunoaffinity. Purified E1E2 heterodimer was recognized by conformation-dependent monoclonal antibodies, showing that the proteins were properly folded. In addition, it interacted with human CD81, a putative HCV receptor, as well as with human low and very low density lipoproteins, which have been shown to be associated with infectious HCV particles isolated from patients. Purified E1E2 heterodimer was also reconstituted into liposomes. E1E2-liposomes were recognized by a conformation-dependent monoclonal antibody as well as by human CD81. Together, these data indicate that E1E2-liposomes are a valuable tool to study the molecular requirements for HCV binding to target cells.

Structural studies of human enteric adenovirus type 41

Enteric adenoviruses of serotypes 40 and 41 possess some specific structural features, one of which is the presence on the virion of two fibers of different lengths and primary sequences. These viruses are notoriously difficult to grow under laboratory conditions. In this paper the successful growth and purification of Ad41 are presented in detail. Structural Ad41 proteins were analyzed by biochemical methods, mass spectrometry, and electron microscopy (EM), in order to identify and localize them on polyacrylamide denaturing gels and to assess the proportion of short and long fibers in the virion. Surprisingly, the three proteins composing virus short and long pentons did not totally enter the denaturing polyacrylamide gels, which is probably due in part to their high pI. The pentons were separately purified and their dimensions were estimated from EM data. The EM images suggest that there are the same amounts of short and long fibers in each virion.

Particle formation by a conserved domain of the herpes simplex virus protein VP22 facilitating protein and nucleic acid delivery

VP22, a structural protein of herpes simplex virus, exhibits unusual trafficking properties which we proposed might be exploited in gene and protein delivery applications. To pursue the use of the protein itself for cargo delivery into cells, we developed an expression system for the C-terminal half of VP22, residues 159-301 (VP22.C1), and purified the protein in high yields. Addition of short oligonucleotides (ODNs) induced the assembly of novel particles, which were regular spheres with a size range of 0.3 to 1.0 microm in diameter, incorporating both protein and ODN. Following the particles in living cells using fluorescently tagged ODNs, we show that they enter efficiently within 2-4 h, and reside stably in the cell cytoplasm for up to several days. Remarkably, however, light activation induced particle disruption and release of the protein and ODN to the nucleus and cytoplasm within seconds, a process that we have captured by time lapse microscopy. In addition to delivering antisense ODNs, ribozymes, and RNA/DNA hybrids, the VP22.C1 protein could also be modified to include peptides or proteins. These particles have the potential for delivery of a wide range of therapeutic agents in gene therapy and vaccine development.

The VP1-unique region of parvovirus B19: amino acid variability and antigenic stability

The unique region of structural protein VP1 of parvovirus B19 (erythrovirus B19) is important for eliciting neutralizing antibodies that are responsible for eliminating the virus from the peripheral blood and for inducing lifelong immunity. Neutralizing human MAbs bind a conformationally defined epitope spanning VP1 residues 30-42. The DNA sequence encoding the VP1-unique region was determined in parvovirus B19 isolated from peripheral blood and amniotic fluid of nine acutely infected pregnant women, five arthritis patients and two chronically infected children. The amino acid sequences of the VP1-unique region exhibited higher variability in comparison with other B19-specific proteins. To analyse the influence of amino acid variations on antibody binding and protein conformation, two variants of the VP1-unique region were selected and expressed in E. coli as intein-fusion proteins. The selected variants displayed a number of amino acid exchanges in the VP1-unique region and had mutations in the determined epitope and adjacent regions. After purification via affinity chromatography, the dissociation constants K(D) of VP1-specific human MAbs interacting with the variant antigens and a viral prototype of the VP1-unique region were determined with a quartz crystal microbalance biosensor. A value of 5.4 x 10(-8) M was determined for the prototype isolate pJB; the affinity constants for the variant VP1-unique regions were similar. Comparable values were obtained for interaction of antibodies with non-infectious VP1/VP2 capsids produced by recombinant baculovirus and with B19 virions from amniotic fluid. It is concluded that the conformation of the epitope is unaffected by mutations or the environment of the VP1-unique region in virus capsids.

In vitro assembly of bacteriophage P4 procapsids from purified capsid and scaffolding proteins

Bacteriophage P4 is a satellite virus of bacteriophage P2, which has acquired the ability to utilize the structural gene products of P2 to assemble its own capsid. The normal P2 capsid has a T = 7 icosahedral structure comprised of the gpN-derived capsid protein, whereas the capsid produced under the control of P4 has a smaller, T = 4 structure. The protein responsible for this size determination is the P4-coded gene product Sid, which forms an external scaffold on the P4 procapsid. Using an in vitro assembly system, we show that gpN and Sid can coassemble into procapsid-like particles, indistinguishable from those produced in vivo, in the absence of any other gene products. The fidelity of the assembly reaction is enhanced by the inclusion of PEG and has a pH optimum between 8.0 and 8.5. Analysis of the assembly properties of truncated versions of Sid and gpN suggests that the amino-terminal part of Sid is involved in gpN binding, while the carboxyl-terminal part forms trimeric Sid-Sid interactions, and that the first 31 amino acids of gpN are required for binding to Sid as well as for size determination.

Functional dissection of the major structural protein of bluetongue virus: identification of key residues within VP7 essential for capsid assembly

A lattice of VP7 trimers forms the surface of the icosahedral bluetongue virus (BTV) core. To investigate the role of VP7 oligomerization in core assembly, a series of residues for substitution were predicted based on crystal structures of BTV type 10 VP7 molecule targeting the monomer-monomer contacts within the trimer. Seven site-specific substitution mutations of VP7 have been created using cDNA clones and were employed to produce seven recombinant baculoviruses. The effects of these mutations on VP7 solubility, ability to trimerize and formation of core-like particles (CLPs) in the presence of the scaffolding VP3 protein, were investigated. Of the seven VP7 mutants examined, three severely affected the stability of CLP, while two other mutants had lesser effect on CLP stability. Only one mutant had no apparent effect on the formation of the stable capsid. One mutant in which the conserved tyrosine at residue 271 (lower domain helix 6) was replaced by arginine formed insoluble aggregates, implying an effect in the folding of the molecule despite the prediction that such a change would be accommodated. All six soluble VP7 mutants were purified, and their ability to trimerize was examined. All mutants, including those that did not form stable CLPs, assembled into stable trimers, implying that single substitution may not be sufficient to perturb the complex monomer-monomer contacts, although subtle changes within the VP7 trimer could destabilize the core. The study highlights some of the key residues that are crucial for BTV core assembly and illustrates how the structure of VP7 in isolation underrepresents the dynamic nature of the assembly process at the biological level.

Norwalk virus open reading frame 3 encodes a minor structural protein

Norwalk virus (NV) is a causative agent of acute epidemic nonbacterial gastroenteritis in humans. The inability to cultivate NV has required the use of molecular techniques to examine the genome organization and functions of the viral proteins. The function of the NV protein encoded by open reading frame 3 (ORF 3) has been unknown. In this paper, we report the characterization of the NV ORF 3 protein expressed in a cell-free translation system and in insect cells and show its association with recombinant virus-like particles (VLPs) and NV virions. Expression of the ORF 3 coding region in rabbit reticulocyte lysates resulted in the production of a single protein with an apparent molecular weight of 23,000 (23K protein), which is not modified by N-linked glycosylation. The ORF 3 protein was expressed in insect cells by using two different baculovirus recombinants; one recombinant contained the entire 3' end of the genome beginning with the ORF 2 coding sequences (ORFs 2+3), and the second recombinant contained ORF 3 alone. Expression from the construct containing both ORF 2 and ORF 3 resulted in the expression of a single protein (23K protein) detected by Western blot analysis with ORF 3-specific peptide antisera. However, expression from a construct containing only the ORF 3 coding sequences resulted in the production of multiple forms of the ORF 3 protein ranging in size from 23,000 to 35,000. Indirect-immunofluorescence studies using an ORF 3 peptide antiserum showed that the ORF 3 protein is localized to the cytoplasm of infected insect cells. The 23K ORF 3 protein was consistently associated with recombinant VLPs purified from the media of insect cells infected with a baculovirus recombinant containing the entire 3' end of the NV genome. Western blot analysis of NV purified from the stools of NV-infected volunteers revealed the presence of a 35K protein as well as multiple higher-molecular-weight bands specifically recognized by an ORF 3 peptide antiserum. These results indicate that the ORF 3 protein is a minor structural protein of the virion.

Purification and protein composition of PM2, the first lipid-containing bacterial virus to be isolated

The marine, icosahedral bacteriophage PM2 was isolated in the late 1960s. It was the first phage for which lipids were firmly demonstrated to be part of the virion structure and it has been classified as the type organism of the Corticoviridae family. The host, Pseudoalteromonas espejiana BAL-31, belongs to a common group of marine bacteria. We developed a purification method producing virions with specific infectivity approximately as high as that of the lipid-containing phages PRD1 and &phi;6. The sensitivity of the virus to normally used purification media such as those containing sucrose is demonstrated. We also present an alternative host, a pseudoalteromonad, that allows enhanced purification of the virus under reduced salt conditions. We show, using N-terminal amino acid sequencing and comparison with the genomic sequence, that there are at least eight structural proteins in the infectious virus.

Proteolytic processing in infectious bursal disease virus: identification of the polyprotein cleavage sites by site-directed mutagenesis

The infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is the causative agent of an immune depressive disease that affects domesticated and wild avian species. The expression strategy of IBDV includes the synthesis of a 110-kDa polyprotein containing the capsid precursor polypeptides. The polyprotein is autocatalitically processed rendering three polypeptides: NH2-VPX-VP4-VP3-COOH. We have carried out a systematic analysis, using a series of plasmids encoding polyproteins containing either deletions or single amino acid substitutions, to identify the processing sites. The results obtained showed the existence of two sites, 511LAA513 and 754MAA756, that are essential for the processing of the VPX-VP4 and VP4-VP3 precursors, respectively. These sequences are highly conserved among IBDV strains form serotypes 1 and 2. A secondary VPX-VP4 processing site was detected in a 19-amino acid stretch located upstream of the 511LAA513 site. Analyses using versions of the 754MAA756 VP4-VP3 processing site containing conservative and nonconservative amino acid substitutions demonstrated that the specificity of the cleavage is dictated by the conserved AA dipeptide.

Ni-NTA-gold clusters target His-tagged proteins

Addition of six histidines to recombinant proteins has proved useful in their purification by nickel-affinity columns. This technology was adapted by synthesizing the chelator for nickel (nitrilotriacetic acid, NTA) onto the surface of gold clusters. These Ni-NTA-gold clusters were shown to specifically target the 6His region of tagged proteins. Results were verified by column chromatography, dot and overlay blots, UV-Vis spectroscopy, and scanning transmission electron microscopy. A 6His-tagged adenovirus "knob" protein was also shown to maintain receptor binding activity after gold labeling. Two types of gold clusters were used: 1.4-nm Nanogold and a new 1.8-nm "PeptideGold" coated with an NTA-dipeptide-thiol. These novel labels should be useful in site-specific high-resolution EM labeling, as well as in metallographic development, detection in the light microscope, or direct visualization.

Chimeric infectious bursal disease virus-like particles expressed in insect cells and purified by immobilized metal affinity chromatography

Chimeric virus-like particles (VLPs) of infectious bursal disease virus (IBDV) were produced by coinfecting Spodoptera frugiperda (Sf-9) insect cells with two recombinant baculoviruses, vIBD-7 and vEDLH-22. vIBD-7 encodes VP2, VP3, and VP4 of the IBDV structural proteins. vEDLH-22 encodes VP2 with five histidine residues at the carboxy-terminus (VP2H). Coinfection produced hybrid VLPs composed of VP2, VP2H, and VP3. The additional histidine residues on VP2H enabled the efficient purification of VLPs based on immobilized metal affinity chromatography (IMAC). These results demonstrated that the VLPs formed are comprised of chimeric subunits with attached affinity ligands, and further, that sufficient His5 ligand was available for binding to the IMAC metal-chelating resin. Additionally, these novel particles were fully characterized for antigenicity by a series of monoclonal antibodies, and appeared identical to the two wild-type IBDV strains contributing subunits to the chimeric VLP. IMAC purification provides a promising low-cost and simple scheme to purify VLPs as vaccines.

[HPLC separation and characterization of tick-borne encephalitis and equine Venezuela encephalomyelitis viral proteins]

Homogeneous (according to PAGE) capsid and surface viral proteins were isolated from concentrated purified suspensions of tick-borne encephalitis and Venezuelan equine encephalomyelitis viruses by one-stage reversed-phase HPLC. The amino acid composition and the sequences of their N-terminal parts were determined.

Characteristics of acyrthosiphon pisum virus, a newly identified virus infecting the pea aphid

A new virus was isolated from the pea aphid, Acyrthosiphon pisum, and tentatively named Acyrthosiphon pisum virus (APV). The isometric virus particles were approximately 31 nm in diameter and contained a single-stranded RNA molecule of approximately 10 kb. Four structural proteins were observed with molecular masses of approximately 23.3, 24.2, 34.5, and 66.2 kDa. The 34.5-kDa capsid protein was the most abundant product in purified virions. Computer-assisted analysis revealed no significant homology between an internal sequence of 37 amino acids of the 34.5-kDa protein of APV and other polypeptides of viral origin. APV was not immunologically related to other ssRNA viruses from hemipteroid insects, such as aphid lethal paralysis virus, Rhopalosiphum padi virus, and Nezara viridula virus type 1. Immunolocalization on ultrathin sections of 3-day-old nymphs of A. pisum showed that APV antigen was predominantly present in the epithelial cells of the digestive tract. Virus particles were also observed associated with the microvilli of the intestine. Occasionally, muscle cells and mycetocyte cells were found infected. Purified APV, fed to 1-day-old A. pisum nymphs, significantly reduced the growth of the aphid and increased the time needed to reach maturity.

The major antigenic protein of infectious bursal disease virus, VP2, is an apoptotic inducer

Infectious bursal disease virus (IBDV) is the causative agent of an economically important poultry disease. Vaccinia virus recombinants expressing the IBDV mature structural capsid proteins VP2 and VP3 were generated by using vectors for inducible gene expression. Characterization of these recombinant viruses demonstrated that expression of VP2 leads to induction of apoptosis in a variety of mammalian cell lines. Transfection of cell cultures with a expression vector containing the VP2 coding region under the control of the immediate-early promoter-enhancer region of human cytomegalovirus also triggers programmed cell death. The apoptotic effect of VP2 is efficiently counteracted by coexpression of the proto-oncogene bcl-2. The results presented demonstrate that VP2 is a bona fide apoptotic inducer. Evaluation of the significance of this finding for the virus life cycle must await further research.

Coronavirus genomic and subgenomic minus-strand RNAs copartition in membrane-protected replication complexes

The majority of porcine transmissible gastroenteritis coronavirus plus-strand RNAs (genome and subgenomic mRNAs), at the time of peak RNA synthesis (5 h postinfection), were not found in membrane-protected complexes in lysates of cells prepared by Dounce homogenization but were found to be susceptible to micrococcal nuclease (85%) or to sediment to a pellet in a cesium chloride gradient (61%). They therefore are probably free molecules in solution or components of easily dissociable complexes. By contrast, the majority of minus-strand RNAs (genome length and subgenomic mRNA length) were found to be resistant to micrococcal nuclease (69%) or to remain suspended in association with membrane-protected complexes following isopycnic sedimentation in a cesium chloride gradient (85%). Furthermore, 35% of the suspended minus strands were in a dense complex (1.20 to 1.24 g/ml) that contained an RNA plus-to-minus-strand molar ratio of approximately 8:1 and viral structural proteins S, M, and N, and 65% were in a light complex (1.15 to 1.17 g/ml) that contained nearly equimolar amounts of plus- and minus-strand RNAs and only trace amounts of proteins M and N. In no instance during fractionation were genome-length minus strands found segregated from sub-genome-length minus strands. These results indicate that all minus-strand species are components of similarly structured membrane-associated replication complexes and support the concept that all are active in the synthesis of plus-strand RNAs.

Immunogenic, non-infectious polio subviral particles synthesized in Saccharomyces cerevisiae

Polioviral genes coding for P1, the precursor for the structural proteins, and 3CD, the viral protease, were cloned in a Saccharomyces cerevisiae inducible expression system. N-antigenic empty capsids could be isolated from the yeast cell extract provided that pirodavir, a capsid-binding compound and capsid stabilizer, was added during the induction period and during purification. Purification was by immunoaffinity chromatography. The purified empty capsids had the same immunogenicity as poliovirus virions. The techniques described might be useful for the production of new non-infectious vaccines.

Expression of the dengue virus structural proteins in Pichia pastoris leads to the generation of virus-like particles

We have expressed cDNA encoding the dengue virus structural proteins in Pichia pastoris by chromosomal integration of an expression cassette containing the dengue virus structural genes (CprME). The yeast recombinant E protein migrated during SDS-PAGE as a 65 kDa protein when analysed by Western blotting and radioimmunoprecipitation, which is the expected molecular mass for correctly processed and glycosylated E protein. Treatment with endoglycosidases showed that the recombinant E protein was modified by the addition of short mannose chains. The E protein migrated with a buoyant density of 1.13 g/cm3 when analysed using sucrose density gradient centrifugation. Spherical structures with an average diameter of 30 nm, whose morphology resembles dengue virions, were observed in the purified fractions using transmission electron microscopy. Furthermore, the virus-like particles were immunogenic in animals and were able to induce neutralizing antibodies. This is the first report that expression of the structural genes of a flavivirus in yeast is able to generate particulate structures that resemble virions.

A solid-phase enzyme linked immunosorbent assay using monoclonal antibodies, for the detection of African swine fever virus antigens and antibodies

An improved solid-phase enzyme linked immunosorbent assay (ELISA) using monoclonal antibodies was developed to detect an African swine fever virus protein (VP73) in pig samples. The use of monoclonal antibodies against VP73 allowed a sensitive and specific sandwich ELISA. This assay detected a limiting antigen concentration of 0.05 microgram/ml of VP73, lower than the detection limit of 0.6 microgram/ml obtained by using polyclonal antibodies by the same ELISA. The whole virus particle was detected with this method to a limit of 2.3 x 10(2) PFU/ml. At the same time, an indirect ELISA was developed to detect ASFV antibodies. The results also indicate that this method may be a useful technique for epidemiological surveys.

Characterization of JKT-7400, an orbivirus which grows in Aedes albopictus mosquito cells: evidence pointing to a minor virion protein, VP6, as the RNA guanylyltransferase

JKT-7400 virus, an orbivirus originally isolated from Culex mosquitos, was plaque purified and adapted to Aedes albopictus mosquito cells. Conditions which enhance viral cytopathic effect and optimize plaque formation are described. In contrast to bluetongue virus, the prototype orbivirus, no replication of JKT-7400 virus in vertebrate cells was observed. The core particle of JKT-7400 virus contains 10 segments of dsRNA and three minor proteins, VP1, VP4, and VP6. The inner shell contains two major proteins, VP2 and VP7, and the outer shell consists of the other two major proteins, VP3 and VP5. Evidence is presented suggesting that the viral protein associated with the capping of virus mRNA, i.e., the guanylyltransferase, is VP6, one of the core proteins.

Biochemical characterization of FMDV A10 and A22 subtypes by PAGE and IEF

Both polyacrylamide gel electrophoresis (PAGE) and iso-electric focusing (IEF) have been standardized using the sucrose density gradient purified 146S particles of FMD virus subtypes A10 and A22. Differences in the molecular weights of structural proteins (VP1, VP2 and VP3 of two subtypes (A10 and A22) of FMDV have been revealed in PAGE but no appreciable differences in the pI of VP1, VP2 and VP3 is found in IEF.

Efficient gene transfer by a human immunodeficiency virus type 1 (HIV-1)-derived vector utilizing a stable HIV packaging cell line

By transfecting fibroblast cells with an HIV-1-MN molecular clone with a deletion of the major packaging sequence, we have developed a stable HIV-1 packaging cell line, psi 422, psi 422 cells form syncytia with CD4-positive cells, correctly express HIV-1 structural proteins, and produce a large amount of mature particles with normal reverse transcriptase activity. Yet these particles, in which RNA was not detected by reverse transcriptase-PCR, are not infectious. When stably transfected with an HIV-1-based retroviral vector, the psi 422 cell line produces virions capable of transducing CD4-positive cells with high efficiency (up to 10(5) cells per ml). The availability of this stable noninfectious HIV-1 packaging cell line capable of generating high-titer HIV-1 vectors represents a new step toward the use of an HIV-1 delivery system in gene therapy.