- Volume 91, Issue 11, 2010
Volume 91, Issue 11, 2010
- Animal
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- DNA viruses
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Identification of binding domains in the herpes simplex virus type 1 small capsid protein pUL35 (VP26)
More LessIn this study, fragments of the small capsid protein pUL35 (VP26) from herpes simplex virus type 1 (HSV-1) were generated to identify binding domains for a number of known ligands. Analysis of the binding of dynein light chain subunits, DYNLT1 and DYNLT3, as well the HSV-1 structural proteins pUL19 (VP5) and pUL37 was then undertaken using the LexA yeast two-hybrid assay. The N-terminal half of pUL35, in particular residues 30–43, was identified as a common region for the binding of DYNLT1 and DYNLT3. Additional distinct regions in the C terminus of pUL35 also contribute to the binding of DYNLT1 and DYNLT3. In contrast, only the C-terminal half of pUL35 was found to mediate the binding of pUL19 and pUL37 through distinct regions. The relevance of this information to the role of pUL35 in viral transport and assembly is discussed.
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Murine cytomegalovirus major immediate-early protein 3 interacts with cellular and viral proteins in viral DNA replication compartments and is important for early gene activation
More LessMurine cytomegalovirus (MCMV) immediate-early protein 3 (IE3) is essential for successful viral infection. This study developed MCMVs with an EGFP-fused IE3 gene in order to study IE3 gene expression, subnuclear distribution and biological function, as well as to examine the interaction of IE3 with cellular and viral proteins. The generated viruses included MCMVIE3gfp, in which IE1 was completely removed by the in-frame fusion of exons 3 and 5 and the C terminus of IE3 was tagged with EGFP, and MCMVIE1/3gfp, in which IE1 was kept intact and EGFP was also fused to the C terminus of IE3. Unlike human CMV (HCMV), whose growth was significantly reduced when IE2 (the HCMV homologue of IE3 in MCMV) was tagged with EGFP, MCMVs with IE3–EGFP presented an unchanged replication profile. Using these new constructs, the distribution of IE3 was revealed as well as its interaction with viral and cellular proteins, especially proteins pertaining to DNA replication (M44 and E1) and cellular intrinsic defence [promyelocytic leukemia protein and histone deacetylases (HDACs)]. It was also shown that IE3 domains co-localize with DNA replication domains, and IE3 attracted other required proteins into IE3 domains via protein–protein interactions. In addition, IE3 was shown to interact with HDAC2 and to eliminate the inhibitory effect of HDAC2 on early viral gene production. Together, these results suggest that IE3 acts as a key protein for viral DNA replication by establishing pre-replication domains via recruitment of the required viral and cellular proteins, and by reducing host defences.
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- Plant
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Outer-capsid P8 proteins of phytoreoviruses mediate secretion of assembled virus-like particles from insect cells
Phytoreoviruses are composed of two concentric capsid layers that surround a viral genome. The capsids are formed mainly by the inner-capsid P3 protein and the outer-capsid P8 protein. During the infection of insect-vector cells, these play important roles in packaging the viral genome and the enzymes required for its transcription. P3 and P8 proteins, when co-expressed in Spodoptera frugiperda cells, co-localized in cells and were released as spherical clusters. In contrast P3 proteins expressed in the absence of P8 protein were associated with the cells when they were examined by confocal microscopy. Cryo-electron microscopy revealed that the secreted clusters, composed of P3 and P8 proteins, were double-layered virus-like particles that were indistinguishable from intact viral particles. Our results indicate that P8 proteins mediate the secretion of assembled virus-like particles from S. frugiperda insect cells and, therefore, most probably from insect-vector cells also.
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The helper-component protease transmission factor of tobacco etch potyvirus binds specifically to an aphid ribosomal protein homologous to the laminin receptor precursor
Potyviruses are plant pathogens transmitted by aphids in a non-persistent manner. During transmission, the virus-encoded factor helper-component protease (HCPro) is presumed to act as a molecular bridge, mediating the reversible retention of virions to uncharacterized binding sites in the vector mouthparts. Whilst the predicted interaction between HCPro and the coat protein (CP) of virions has been confirmed experimentally, the characterization of putative HCPro-specific receptors in aphids has remained elusive, with the exception of a report that described binding of HCPro of zucchini yellow mosaic virus to several cuticle proteins. To identify other aphid components that could play a role during transmission, this study used purified HCPro of tobacco etch virus (TEV) in far-Western blotting assays as bait to select interactors among proteins extracted from aphid heads. With this approach, new HCPro-interacting proteins were found, and several were identified after mass spectrometry analysis and searches in databases dedicated to aphid sequences. Among these interactors, a ribosomal protein S2 (RPS2) was chosen for further investigation due to its homology with the laminin receptor precursor, known to act as the receptor of several viruses. The specific interaction between RPS2 and TEV HCPro was confirmed after cloning and heterologous expression of the corresponding Myzus persicae gene. The possible involvement of RPS2 in the transmission process was further suggested by testing a variant of HCPro that was non-functional for transmission due to a mutation in the conserved KITC motif (EITC variant). This variant retained its ability to bind CP but failed to interact with RPS2.
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- Other Agents
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Biochemical and immunohistochemical characterization of feline spongiform encephalopathy in a German captive cheetah
Feline spongiform encephalopathy (FSE) is a transmissible spongiform encephalopathy that affects domestic cats (Felis catus) and captive wild members of the family Felidae. In this report we describe a case of FSE in a captive cheetah from the zoological garden of Nuremberg. The biochemical examination revealed a BSE-like pattern. Disease-associated scrapie prion protein (PrPSc) was widely distributed in the central and peripheral nervous system, as well as in the lymphoreticular system and in other tissues of the affected animal, as demonstrated by immunohistochemistry and/or immunoblotting. Moreover, we report for the first time the use of the protein misfolding cyclic amplification technique for highly sensitive detection of PrPSc in the family Felidae. The widespread PrPSc deposition suggests a simultaneous lymphatic and neural spread of the FSE agent. The detection of PrPSc in the spleen indicates a potential for prion infectivity of cheetah blood.
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