Altered ultrastructure of rinderpest virus and its nucleocapsids induced by 5-fluorouracil

he ultrastructure of purified rinderpest virus and intracellular viral nucleocapsids from infected vero cells treated with a subtoxic dose of 5-fluorouracil (5-Fu) (1 mug/ml), has been analysed by transmission electron microscopy, and compared with that of normal virus particle and nucleocapsids. The results reveal dramatic alterations in the structure of both virions and nucleocapsids. The surface glycoprotein projection of virions was not seen or present at a much reduced level. The intracellular nucleocapsids showed pronounced structural changes,with respect to size, shape and fine structure. The length of treated nucleocapsids is much smaller as compared to the control. The central hollow core is missing in case of drug-treated nucleocapsid and the herring bone structure is replaced by a 'beads on string' structure. The presence of N protein, which is a major structural component of nucleocapsids was seen in 5-Fu-treated cells, but it was associated with a predominantly diffused form of nucleocapsids as seen by immunoelectron microscopy. We report here the first definitive and visual evidence of altered structure of virions and their nucleocapsids after 5-Fu treatment

Primary structure of sesbania mosaic virus coat protein: its implications to the assembly and architecture of the virus

Sesbania mosaic virus (SMV) is a plant virus that infects Sesbania grandiflora plants in Andhra Pradesh, India. The amino acid sequence of the coat protein of SMV was determined using purified peptides generated by cleavage with trypsin, chymotrypsin, V8 protease and clostripain. The 230 residues so far determined were compared to the corresponding residues of southern bean mosaic virus (SBMV), the type member of sobemoviruses. The overall identity between the sequences is 61.7%. The amino terminal 64 residues, which constitute an independent domain (R-domain) known to interact with RNA, are conserved to a lower extent (52.5%). Comparison of the positively charged residues in this domain suggests that the RNA-protein interactions are considerably weaker in SMV. The residues that constitute the major domain of the coat protein, the surface domain (S-domain, residues 65-260), are better conserved (66.5%). The positively charged residues of this domain that face the nucleic acid are well conserved. The longest conserved stretch of residues (131-142) corresponds to the loop involved in intersubunit interactions between subunits related by the quasi 3-fold symmetry. A unique cation binding site located on the quasi 3-fold axis contributes to the stability of SMV. These differences are reflected in the increased stability of the SMV coat protein and its ability to be reconstituted with RNA at pH 7.5. A major epitope was identified using monoclonal antibodies to SMV in the segment 201-223 which contains an exposed helix in the capsid structure. This region is highly conserved between SMV and SBMV (70%) suggesting that it could represent the site of an important function such as vector recognition.

Immune responses to hemagglutinin-neuraminidase protein of peste des petits ruminants virus expressed in transgenic peanut plants in sheep

Peste des petits ruminants (PPR) is an acute, highly contagious disease of small ruminants caused by a morbillivirus, Peste des petits ruminants virus (PPRV). The disease is prevalent in equatorial Africa, the Middle East, and the Indian subcontinent. A live attenuated vaccine is in use in some of the countries and has been shown to provide protection for at least three years against PPR. However, the live attenuated vaccine is not robust in terms of thermotolerance. As a step towards development of a heat stable subunit vaccine, we have expressed a hemagglutinin-neuraminidase (HN) protein of PPRV in peanut plants (Arachis hypogea) in a biologically active form, possessing neuraminidase activity. Importantly. HN protein expressed in peanut plants retained its immunodominant epitopes in their natural conformation. The immunogenicity of the plant derived HN protein was analyzed in sheep upon oral immunization. Virus neutralizing antibody responses were elicited upon oral immunization of sheep in the absence of any mucosal adjuvant. In addition, anti-PPRV-HN specific cell-mediated immune responses were also detected in mucosally immunized sheep. (C) 2010 Elsevier B.V. All rights reserved.

Characterization of an in vitro transcription system from rinderpest virus

An in vitro transcription system for rinderpest virus (RPV) is described. Ribonucleoprotein complexes isolated from RPV-infected Vero cells, human lung carcinoma cells, or detergent-disrupted purified virions synthesized authentic RPV mRNAs for the N, P, M, F and H genes as identified by dot blot hybridization analysis with individual cDNA clones. The relative abundance of the mRNAs synthesized in vitro decreased from the 3? end of the genome to the 5? end, very similar to that observed with measles virus transcription in vitro. The transcription by purified virions was stimulated three-fold by the addition of infected human lung carcinoma cell lysate, demonstrating the involvement of host factor(s) in mRNA synthesis.

Molecular and serological studies on the recent seal virus epizootics in Europe and Siberia

The virus epizootics which occurred in seals in both Europe and Siberia during 1987/1988 were caused by two different morbillivirus, referred to as phocid distemper virus (PDV) 1 and 2, respectively. Molecular and serological studies have shown that the European virus is quite distinct from canine distemper virus (CDV), its closest relative in the morbillivirus group. Analysis of tissues obtained from infected seals from a wide geographical distrubution over Northern Europe showed that the infectious agent (PDV 1) was identical in all cases. Nucleotide sequence analysis of one of the virus genes suggested that this virus has evolved away from CDV over a long time period and is most probably an enzootic virus of marine mammals. In contrast, the virus (PDV 2) which caused the deaths of many Siberian seals was indistinguishable, both serologically and at the molecular level, from CDV and must have originated from a land source.

Interactions of 3' terminal and 5' terminal regions of physalis mottle virus genomic RNA with its replication complex

Physalis mottle virus (PhMV) belongs to the tymogroup of positive-strand RNA viruses with a genome size of 6 kb. Crude membrane preparations from PhMV-infected Nicotiana glutinosa plants catalyzed the synthesis of PhMV genomic RNA from endogenously bound template. Addition of exogenous genomic RNA enhanced the synthesis which was specifically inhibited by the addition of sense and antisense transcripts corresponding to 3' terminal 242 nucleotides as well as the 5' terminal 458 nucleotides of PhMV genomic RNA while yeast tRNA or ribosomal RNA failed to inhibit the synthesis. This specific inhibition suggested that the 5' and 3' non-coding regions of PhMV RNA might play an important role in viral replication.

Protection of adult but not newborn mice against lethal intracerebral challenge with Japanese encephalitis virus by adoptively transferred virus-specific cytotoxic T lymphocytes: Requirement for L3T4(+) T cells

The protective ability of cytotoxic T cells (CTL) raised in vitro against Japanese encephalitis virus (JEV) was examined by adoptive transfer experiments. Adoptive transfer of anti-JEV effecters by intracerebral (i.c.) but not by intraperitoneal (i.p.) or intravenous (i.v.) routes protected adult BALB/c mice against lethal i.c. JEV challenge. In contrast to adult mice, adoptive transfer of anti-JEV effecters into newborn (4-day-old) and suckling (8-14-day-old) mice did not confer protection. However, virus-induced death was delayed in suckling mice compared to newborn mice upon adoptive transfer. The specific reasons for lack of protection in newborn mice are not clear but virus load was found to be higher in newborn mice brains compared to those of adults and virus clearance was observed only in adult mice brains but not in newborn mice brains upon adoptive transfer. Specific depletion of Lyt 2.2(+), L3T4(+) or Thy-1(+) T cell populations before adoptive transfer abrogated the protective ability of transferred effecters. However, when Lyt 2.2(+) cell-depleted and L3T4(+) cell-depleted effecters were mixed and transferred into adult mice the protective activity was retained, demonstrating that both Lyt 2.2(+) and L3T4(+) T cells are necessary to confer protection. Although the presence of L3T4(+) T cells in adoptively transferred effector populations enhanced virus-specific serum neutralizing antibodies, the presence of neutralizing antibodies alone without Lyt 2.2(+) cells was not sufficient to confer protection.

Expression of the Japanese encephalitis virus NS3 and NS2b proteins as glutathione S-transferase fusions

Flaviviruses generate their structural and nonstructural proteins by proteolytic processing of a single large polyprotein precursor. These proteolytic events are brought about both by host cell signalase and a virally encoded protease. The virally encoded proteolytic activity has been shown to reside within the nonstructural protein 3 (NS3) and requires the product of the nonstructural 2b (NS2b) gene. In order to obtain sufficient quantities of pure NS2b and NS3 proteins for kinetic analysis, we have expressed both these proteins in recombinant systems as fusions to glutathione S-transferase (GST). The fusion constructs were driven by the strong bacteriophage T7 promoter. Transfection of these constructs into the African green monkey kidney cell line CV-1 previously infected with a recombinant vaccinia virus expressing the T7 RNA polymerase resulted in synthesis of the fusion proteins. Both the fusion proteins could be purified to homogeneity in a single step using a glutathione agarose affinity matrix.

Structure of sesbania mosaic virus at 3 å resolution

Background: Sobemoviruses are a group of RNA plant viruses that have a narrow host range. They are characterized in vitro by their stability, high thermal inactivation point and longevity. The three-dimensional structure of only one virus belonging to this group, southern bean mosaic virus (SBMV), is known. Structural studies on sesbania mosaic virus (SMV), which is closely related to SBMV, will provide details of the molecular interactions that are likely to be important in the stability and assembly of sobemoviruses. Results: We have determined the three-dimensional structure of SMV at 3 Angstrom resolution. The polypeptide fold and quaternary organization are very similar to those of SBMV. The capsid consists of sixty icosahedral asymmetric units, each comprising three copies of a chemically identical coat protein subunit, which are designated as A, B and C and are in structurally different environments. Four cation-binding sites have been located in the icosahedral asymmetric unit. Of these, the site at the quasi-threefold axis is not found in SBMV. Structural differences are observed in loops and regions close to this cation-binding site. Preliminary studies on ethylene diamine tetra acetic acid (EDTA) treated crystals suggest asymmetry in removal of the quasi-equivalent cations at the AB, BC, and AC subunit interfaces. Conclusions: Despite the overall similarity between SMV and SBMV in the nature of the polypeptide fold, these viruses show a number of differences in intermolecular interactions. The polar interactions at the quasi-threefold axis are substantially less in SMV and positively charged residues on the RNA-facing side of the protein and in the N-terminal arm are not particularly well conserved. This suggests that protein-RNA interactions are likely to be different between the two viruses.

Japanese encephalitis virus infection of mouse cell lines: ability to prime mice for generation of virus specific cytotoxic T lymphocytes and differences in CTL recognisable viral determinants

Ten different mouse cell lines were examined for Japanese encephalitis virus (JEV) infection in vitro and then tested for their ability to generate virus specific cytotoxic T lymphocytes (CTL). Among all cell lines examined, Neuro La (a neuroblastoma) was readily infected with JEV as examined by immunofluorescence and viral replication. Among other cells, P388D1, RAW 264.7 (Macrophage origin), Sp2/0 (B-cell Hybridoma), YAC-1 (T-cell lymphoma), and L929 (Fibroblast) were semipermissive to JEV infection. The cytopathic effects caused by progressive JEV infection varied from cell line to cell line. In the case of YAC-1 cells long-term viral antigen expression was observed without significant alterations in cell viability. Intermediate degrees of cytopathicity are seen in RAW 264.7 and L929 cells while infection of PS, Neuro 2a, P388D1 and Sp2/0 caused major viability losses. All infected cell lines were able to prime adult BALB/c (H-2(d)) mice for the generation of secondary JEV specific CTL. In contrast to YAC-1, the permissive neuroblastoma cell line Neuro 2a (H-2K(k)D(d)) was found to be least efficient in its ability to stimulate anti-viral CTL generation. Cold target competition studies demonstrated that both Neuro 2a and YAC-1 (H-2K(k)D(d)) cells expressed similar viral determinants that are recognised by CTL, suggesting that the reason for the lower ability of Neuro 2a to stimulate anti-viral CTL was not due to lack of viral CTL determinants. These findings demonstrate that a variety of mouse cell lines can be infected with Japanese encephalitis virus, and that these infected cells could be utilised to generate virus specific CTL in BALB/c mice.

In vivo clearance of Japanese encephalitis virus by adoptively transferred virus specific cytotoxic T lymphocytes

Japanese encephalitis virus (JEV) is a positive stranded RNA virus that belongs to the flavivirus group, JEV infection damages the central nervous system (CNS) and is one of the main causative agents of acute encephalitis, H-2 restricted virus-specific cytotoxic T lymphocytes (CTL) have been generated specifically against JEV in our laboratory and these CTL have been shown to protect mice against lethal challenge with JEV, Virus replication was found to be inhibited in the brains of animals that mere adoptively transferred with JEV specific CTL as revealed by immunohistological staining as,veil as viral plaque assays. We further show that virus specific CTL could be recovered from such protected mice as long as 45 days after adoptive transfer.

Inhibition of hepatitis C virus replication by herbal extract: Phyllanthus amarus as potent natural source

Hepatitis C virus infection is a major health problem worldwide. Developing effective antiviral therapy for HCV is the need of the hour. The viral enzymes NS3 protease and NS5B RNA dependent RNA polymerase are essential enzymes for polyprotein processing and viral RNA replication and thus can be potential targets for screening anti-HCV compounds. A large number of phytochemicals are present in plants, which are found to be promising antiviral agents. In this study, we have screened inhibitory effect of different plant extracts against the NS3 and NS5B enzymes of hepatitis C virus. Methanolic extracts were prepared from various plant materials and their inhibitory effects on the viral enzymes were determined by in vitro enzyme assays. Effect on viral RNA replication was investigated by using TaqMan Real time RT-PCR. Interestingly, Phyllanthus amarus root (PAR) extract showed significant inhibition of HCV-NS3 protease enzyme; whereas P. amarus leaf (PAL) extract showed considerable inhibition of NS5B in the in vitro assays. Further, the PAR and PAL extracts significantly inhibited replication of HCV monocistronic replicon RNA and HCV H77S viral RNA in HCV cell culture system. However, both PAR and PAL extracts did not show cytotoxicity in Huh7 cells in the MTT assay. Furthermore, addition of PAR together with IFN-alpha showed additive effect in the inhibition of HCV RNA replication. Results suggest the possible molecular basis of the inhibitory activity of PA extract against HCV which would help in optimization and subsequent development of specific antiviral agent using P. amarus as potent natural source. (C) 2011 Elsevier B.V. All rights reserved.