Expression, purification of herpes simplex virus type 1 UL4 protein, and production and characterization of UL4 polyclonal antibody

VZV IE4 downregulates cellular surface MHC-I via sequestering it to the Golgi complex

Varicella-zoster virus (VZV) infection downregulates surface major histocompatibility complex class I (MHC-I) expression and retains MHC-I in the Golgi complex of infected cells. However, the underlying mechanism is not fully understood. The VZV IE4 protein is a multifunctional protein that is essential for VZV infection. In this study, the human leucocyte antigen C (HLA-C) protein was identified as a novel cellular factor associated with IE4. Ectopically expressed IE4 co-localizes with HLA-C, sequesters HLA-C to the Golgi complex and downregulates cellular surface MHC-I. VZV, with a mutated Golgi localization signal in IE4, denoted as mutated IE4 (mIE4) VZV, was constructed. In mIE4 VZV-infected cells, the cellular surface MHC-I was restored, and HLA-C was not retained in the Golgi complex. In summary, for the first time, we demonstrate a novel role of VZV IE4 in interfering with the MHC-I presentation pathway, suggesting that it may contribute to the evasion of host antiviral adaptive immunity.

NEX-TRAP, a novel method for in vivo analysis of nuclear export of proteins

Transport of proteins between cytoplasm and nucleus is mediated by transport factors of the importin α- and β-families and occurs along a gradient of the small GTPase Ran. To date, in vivo analysis as well as prediction of protein nuclear export remain tedious and difficult. We generated a novel bipartite assay called NEX-TRAP (Nuclear EXport Trapped by RAPamycin) for in vivo analysis of protein nuclear export. The assay is based on the rapamycin-induced dimerization of the modules FRB (FK506-rapamycin (FR)-binding domain) and FKBP (FK506-binding protein-12): a potential nuclear export cargo is fused to FRB, to EYFP for direct visualization as well as to an SV40-derived nuclear localization signal (NLS) for constitutive nuclear import. An integral membrane protein that resides at the trans Golgi network (TGN) is fused to a cytoplasmically exposed FKBP and serves as reporter. EYFP-NLS-FRB fusion proteins with export activity accumulate in the nucleus at steady state but continuously shuttle between nucleus and cytoplasm. Rapamycin-induced dimerization of FRB and FKBP at the TGN traps the shuttling protein outside of the nucleus, making nuclear export permanent. Using several example cargoes, we show that the NEX-TRAP is superior to existing assays owing to its ease of use, its sensitivity and accuracy. Analysis of large numbers of export cargoes is facilitated by recombinational cloning. The NEX-TRAP holds the promise of applicability in automated fluorescence imaging for systematic analysis of nuclear export, thereby improving in silico prediction of nuclear export sequences.

Characterization of a conserved interaction between DNA glycosylase and ParA in Mycobacterium smegmatis and M. tuberculosis

The chromosome partitioning proteins, ParAB, ensure accurate segregation of genetic materials into daughter cells and most bacterial species contain their homologs. However, little is known about the regulation of ParAB proteins. In this study, we found that 3-methyladenine DNA glycosylase I MsTAG(Ms5082) regulates bacterial growth and cell morphology by directly interacting with MsParA (Ms6939) and inhibiting its ATPase activity in Mycobacterium smegmatis. Using bacterial two-hybrid and pull-down techniques in combination with co-immunoprecipitation assays, we show that MsTAG physically interacts with MsParA both in vitro and in vivo. Expression of MsTAG under conditions of DNA damage induction exhibited similar inhibition of growth as the deletion of the parA gene in M. smegmatis. Further, the effect of MsTAG on mycobacterial growth was found to be independent of its DNA glycosylase activity, and to result instead from direct inhibition of the ATPase activity of MsParA. Co-expression of these two proteins could counteract the growth defect phenotypes observed in strains overexpressing MsTAG alone in response to DNA damage induction. Based on protein co-expression and fluorescent co-localization assays, MsParA and MsTAG were further found to co-localize in mycobacterial cells. In addition, the interaction between the DNA glycosylase and ParA, and the regulation of ParA by the glycosylase were conserved in M. tuberculosis and M. smegmatis. Our findings provide important new insights into the regulatory mechanism of cell growth and division in mycobacteria.

Herpes simplex virus 1 tegument protein US11 downmodulates the RLR signaling pathway via direct interaction with RIG-I and MDA-5

The interferon (IFN)-mediated antiviral response is a major defense of the host immune system. In order to complete their life cycle, viruses must modulate host IFN-mediated immune responses. Herpes simplex virus 1 (HSV-1) is a large DNA virus containing more than 80 genes, many of which encode proteins that are involved in virus-host interactions and show immune modulatory capabilities. In this study, we demonstrate that the US11 protein, an RNA binding tegument protein of HSV-1, is a novel antagonist of the beta IFN (IFN-β) pathway. US11 significantly inhibited Sendai virus (SeV)-induced IFN-β production, and its double-stranded RNA (dsRNA) binding domain was indispensable for this inhibition activity. Additionally, wild-type HSV-1 coinfection showed stronger inhibition than US11 mutant HSV-1 in SeV-induced IFN-β production. Coimmunoprecipitation analysis demonstrated that the US11 protein in HSV-1-infected cells interacts with endogenous RIG-I and MDA-5 through its C-terminal RNA-binding domain, which was RNA independent. Expression of US11 in both transfected and HSV-1-infected cells interferes with the interaction between MAVS and RIG-I or MDA-5. Finally, US11 dampens SeV-mediated IRF3 activation. Taken together, the combined data indicate that HSV-1 US11 binds to RIG-I and MDA-5 and inhibits their downstream signaling pathway, preventing the production of IFN-β, which may contribute to the pathogenesis of HSV-1 infection.

Expression, purification of herpes simplex virus type 1 US11 protein, and production of US11 polyclonal antibody

Background

The US11 protein of herpes simplex virus type 1 (HSV-1) is a small, highly basic phosphoprotein expressed at late times during infection. To date, the function of US11 protein in cell culture and animal models is poorly understood. To further investigate the function of the US11 protein, this study was undertaken to express the US11 protein and raise a polyclonal antibody.

Results

The US11 gene was cloned into the prokaryotic expression vector pET-32a (+) to express His-tagged US11 protein in Escherichia coli. After purification by nickel affinity chromatography and refolding, the recombinant protein was used to raise the anti-US11 polyclonal antibody. Western blot analysis demonstrated that the US11 protein was specifically recognized by the polyclonal antibody, and immunofluorescent assay also showed that the antibody was able to probe the US11 protein in the cells infected with HSV-1.

Conclusions

In the present study, we obtained a high-level expression of the recombinant US11 protein as well as high titers of rabbit polyclonal antibody specially against US11 protein in HSV-1 infected cells. This special polyclonal antibody provides a good tool for further studying structural and functional characterization of HSV-1 US11 protein.

Varicella-zoster virus immediate-early protein ORF61 abrogates the IRF3-mediated innate immune response through degradation of activated IRF3

Varicella-zoster virus (VZV) infection of differentiated cells within the host and establishment of latency likely requires evasion of innate immunity and limits secretion of antiviral cytokines. Here we report that its immediate-early protein ORF61 antagonizes the beta interferon (IFN-β) pathway. VZV infection down-modulated the Sendai virus (SeV)-activated IFN-β pathway, including mRNA of IFN-β and its downstream interferon-stimulated genes (ISGs), ISG54 and ISG56. Through a primary screening of VZV genes, we found that ORF61 inhibited SeV-mediated activation of IFN-β and ISRE (IFN-stimulated response element) promoter activities but only slightly affected NF-κB promoter activity, implying that the IFN-β pathway may be blocked in the IRF3 branch. An indirect immunofluorescence assay demonstrated that ectopic expression of ORF61 abrogated the detection of IRF3 in SeV-infected cells; however, it did not affect endogenous dormant IRF3 in noninfected cells. Additionally, ORF61 was shown to be partially colocalized with activated IRF3 in the nucleus upon treatment with MG132, an inhibitor of proteasomes, and the direct interaction between ORF61 and activated IRF3 was confirmed by a coimmunoprecipitation assay. Furthermore, Western blot analysis demonstrated that activated IRF3 was ubiquitinated in the presence of ORF61, suggesting that ORF61 degraded phosphorylated IRF3 via a ubiquitin-proteasome pathway. Semiquantitative reverse transcription-PCR (RT-PCR) analysis demonstrated that the level of ISG54 and ISG56 mRNAs was also downregulated by ORF61. Taken together, our results convincingly demonstrate that ORF61 down-modulates the IRF3-mediated IFN-β pathway by degradation of activated IRF3 via direct interaction, which may contribute to the pathogenesis of VZV infection.

Comprehensive characterization of interaction complexes of herpes simplex virus type 1 ICP22, UL3, UL4, and UL20.5

It has been reported that herpes simplex virus type 1 UL3, UL4, and UL20.5 proteins are localized to small, dense nuclear bodies together with ICP22 in infected cells. In the present study, we comprehensively characterized these interactions by subcellular colocalization, coimmunoprecipitation, and bimolecular fluorescence complementation assays. For the first time, it was demonstrated that both UL3 and UL20.5 are targeted to small, dense nuclear bodies by a direct interaction with ICP22, whereas UL4 colocalizes with ICP22 through its interaction with UL3 but not UL20.5 or ICP22. There was no detectable interaction between UL3 and UL20.5.

Production, purification and characterization of polyclonal antibody against the truncated gK of the duck enteritis virus

Duck virus enteritis (DVE) is an acute, contagious herpesvirus infection of ducks, geese, and swans, which has produced significant economic losses in domestic and wild waterfowl. With the purpose of decreasing economic losses in the commercial duck industry, studying the unknown glycoprotein K (gK) of DEV may be a new method for preferably preventing and curing this disease. So this is the first time to product and purify the rabbit anti-tgK polyclonal antibody. Through the western blot and ELISA assay, the truncated glycoprotein K (tgK) has good antigenicity, also the antibody possesses high specificity and affinity. Meanwhile the rabbit anti-tgK polyclonal antibody has the potential to produce subunit vaccines and the functions of neutralizing DEV and anti-DEV infection because of its neutralization titer. Indirect immunofluorescent microscopy using the purified rabbit anti-tgK polyclonal antibody as diagnostic antibody was susceptive to detect a small quantity of antigen in tissues or cells. This approach also provides effective experimental technology for epidemiological investigation and retrospective diagnose of the preservative paraffin blocks.