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The tegument protein pp65 of human cytomegalovirus acts as an optional scaffold protein that optimizes protein uploading into viral particles.

ABSTRACT:

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The mechanisms that lead to the tegumentation of herpesviral particles are only poorly defined. The phosphoprotein 65 (pp65) is the most abundant constituent of the virion tegument of human cytomegalovirus (HCMV). It is, however, nonessential for virion formation. This seeming discrepancy has not met with a satisfactory explanation regarding the role of pp65 in HCMV particle morphogenesis. Here, we addressed the question of how the overall tegument composition of the HCMV virion depended on pp65 and how the lack of pp65 influenced the packaging of particular tegument proteins. To investigate this, we analyzed the proteomes of pp65-positive (pp65pos) and pp65-negative (pp65neg) virions by label-free quantitative mass spectrometry and determined the relative abundances of tegument proteins. Surprisingly, only pUL35 was elevated in pp65neg virions. As the abundance of pUL35 in the HCMV tegument is low, it is unlikely that it replaced pp65 as a structural component in pp65neg virions. A subset of proteins, including the third most abundant tegument protein, pUL25, as well as pUL43, pUL45, and pUL71, were reduced in pp65neg or pp65low virions, indicating that the packaging of these proteins was related to pp65. The levels of tegument components, like pp28 and the capsid-associated tegument proteins pp150, pUL48, and pUL47, were unaffected by the lack of pp65. Our analyses demonstrate that deletion of pp65 is not compensated for by other viral proteins in the process of virion tegumentation. The results are concordant with a model of pp65 serving as an optional scaffold protein that facilitates protein upload into the outer tegument of HCMV particles.

Importance

The assembly of the tegument of herpesviruses is only poorly understood. Particular proteins, like HCMV pp65, are abundant tegument constituents. pp65 is thus considered to play a major role in tegument assembly in the process of virion morphogenesis. We show here that deletion of the pp65 gene leads to reduced packaging of a subset of viral proteins, indicating that pp65 acts as an optional scaffold protein mediating protein upload into the tegument.

SUBMITTER: Reyda S

PROVIDER: S-EPMC4136338 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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The tegument protein pp65 of human cytomegalovirus acts as an optional scaffold protein that optimizes protein uploading into viral particles.

Reyda Sabine S Tenzer Stefan S Navarro Pedro P Gebauer Wolfgang W Saur Michael M Krauter Steffi S Büscher Nicole N Plachter Bodo B

Journal of virology 20140611 17

<h4>Unlabelled</h4>The mechanisms that lead to the tegumentation of herpesviral particles are only poorly defined. The phosphoprotein 65 (pp65) is the most abundant constituent of the virion tegument of human cytomegalovirus (HCMV). It is, however, nonessential for virion formation. This seeming discrepancy has not met with a satisfactory explanation regarding the role of pp65 in HCMV particle morphogenesis. Here, we addressed the question of how the overall tegument composition of the HCMV viri ...[more]

PMID: 24920816

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Project description:UnlabelledHuman cytomegalovirus (HCMV) is an enveloped double-stranded DNA virus that causes severe disease in newborns and immunocompromised patients. During infection, the host cell endosecretory system is remodeled to form the cytoplasmic virion assembly complex (cVAC). We and others previously identified the conserved, multifunctional HCMV virion tegument protein pUL103 as important for cVAC biogenesis and efficient secondary envelopment. To help define its mechanisms of action and predict additional functions, we used two complementary methods, coimmunoprecipitation (co-IP) and proximity biotinylation (BioID), to identify viral and cellular proteins that interact with pUL103. By using the two methods in parallel and applying stringent selection criteria, we identified potentially high-value interactions of pUL103 with 13 HCMV and 18 cellular proteins. Detection of the previously identified pUL103-pUL71 interaction, as well as verification of several interactions by reverse co-IP, supports the specificity of our screening process. As might be expected for a tegument protein, interactions were identified that suggest distinct roles for pUL103 across the arc of lytic infection, including interactions with proteins involved in cellular antiviral responses, nuclear activities, and biogenesis and transport of cytoplasmic vesicles. Further analysis of some of these interactions expands our understanding of the multifunctional repertoire of pUL103: we detected HCMV pUL103 in nuclei of infected cells and identified an ALIX-binding domain within the pUL103 sequence.ImportanceHuman cytomegalovirus (HCMV) is able to reconfigure the host cell machinery to establish a virion production factory, the cytoplasmic virion assembly complex (cVAC). cVAC biogenesis and operation represent targets for development of novel HCMV antivirals. We previously showed that the HCMV tegument protein pUL103 is required for cVAC biogenesis. Using pUL103 as bait, we investigated viral and cellular protein-protein interactions to identify and understand the range of pUL103 functions. We found that pUL103 interacts with cellular antiviral defense systems and proteins involved in organelle biogenesis and transport of cytoplasmic vesicles and is present in infected cell nuclei. These results expand our understanding of the functional repertoire of pUL103 to include activities that extend from the earliest stages of infection through virion assembly and egress.

Project description:Abstract: We have identified a cytomegalovirus virion protein capable of modulating the rapid induction of an interferon-like response in cells that follows virus binding and penetration. Functional genomics revealed a role for the major cytomegalovirus structural protein, pp65 (ppUL83), in counteracting this response. The underlying mechanism involves a differential impact of this structural protein on the regulation of interferon response factor 3 (IRF-3). In contrast, NF-{kappa}B is activated independent of pp65, and neither STAT1 nor STAT3 becomes activated by either virus. pp65 is sufficient to prevent the activation of IRF-3 when introduced alone into cells. pp65 acts by inhibiting nuclear accumulation of IRF-3 and is associated with a reduced IRF-3 phosphorylation state. Thus, this investigation shows that the major structural protein of cytomegalovirus is committed to the modulation of the IRF-3 response, a primary mediator of the type I interferon response. By subverting IRF-3, the virus escapes throwing a central alarm devoted to both immediate antiviral control and regulation of the immune response. Polyadenylated RNA from 107 confluent HFs was purified by using Oligotex (QIAGEN, Valencia, Calif.) from Trizol (Invitrogen)-extracted total RNA. This RNA was prepared, reverse transcribed, labeled with Cy3-dUTP or Cy5-dUTP (Amersham, Little Chalfont, Buckinghamshire, United Kingdom) by random primed synthesis with DNA pol I Klenow (Amersham Life Science, Inc., Cleveland, Ohio), and hybridized to spotted, human cDNA microarrays as previously described. Sequence-verified human cDNA microarrays (HE and HG series, 31,000 spots; HD51 series, 17,000 spots) were produced at Stanford. Images were collected by using a GenePix 4000B microarray scanner, manually flagged to eliminate poor spots and analyzed by GenePix Pro 2.0 (Axon, Union City, Calif.). A replicate experimental design type is where a series of replicates are performed to evaluate reproducibility or as a pilot study to determine the appropriate number of replicates for a subsequent experiments. Keywords: disease_state_design, pathogenicity_design

Dataset Information

The tegument protein pp65 of human cytomegalovirus acts as an optional scaffold protein that optimizes protein uploading into viral particles.

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Importance

Publications

The tegument protein pp65 of human cytomegalovirus acts as an optional scaffold protein that optimizes protein uploading into viral particles.

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