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The capsid protein encoded by U(L)17 of herpes simplex virus 1 interacts with tegument protein VP13/14.

ABSTRACT: The U(L)17 protein (pU(L)17) of herpes simplex virus 1 (HSV-1) likely associates with the surfaces of DNA-containing capsids in a heterodimer with pU(L)25. pU(L)17 is also associated with viral light particles that lack capsid proteins, suggesting its presence in the tegument of the HSV-1 virion. To help determine how pU(L)17 becomes incorporated into virions and its functions therein, we identified pU(L)17-interacting proteins by immunoprecipitation with pU(L)17-specific IgY at 16 h postinfection, followed by mass spectrometry. Coimmunoprecipitated proteins included cellular histone proteins H2A, H3, and H4; the intermediate filament protein vimentin; the major HSV-1 capsid protein VP5; and the HSV tegument proteins VP11/12 (pU(L)46) and VP13/14 (pU(L)47). The pU(L)17-VP13/14 interaction was confirmed by coimmunoprecipitation in the presence and absence of intact capsids and by affinity copurification of pU(L)17 and VP13/14 from lysates of cells infected with a recombinant virus encoding His-tagged pU(L)17. pU(L)17 and VP13/14-HA colocalized in the nuclear replication compartment, in the cytoplasm, and at the plasma membrane between 9 and 18 h postinfection. One possible explanation of these data is that pU(L)17 links the external face of the capsid to VP13/14 and associated tegument components.

SUBMITTER: Scholtes LD

PROVIDER: S-EPMC2897630 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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The capsid protein encoded by U(L)17 of herpes simplex virus 1 interacts with tegument protein VP13/14.

Scholtes Luella D LD Yang Kui K Li Lucy X LX Baines Joel D JD

Journal of virology 20100526 15

The U(L)17 protein (pU(L)17) of herpes simplex virus 1 (HSV-1) likely associates with the surfaces of DNA-containing capsids in a heterodimer with pU(L)25. pU(L)17 is also associated with viral light particles that lack capsid proteins, suggesting its presence in the tegument of the HSV-1 virion. To help determine how pU(L)17 becomes incorporated into virions and its functions therein, we identified pU(L)17-interacting proteins by immunoprecipitation with pU(L)17-specific IgY at 16 h postinfecti ...[more]

PMID: 20504930

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Project description:UnlabelledHerpesviruses have a characteristic particle structure comprising an icosahedral capsid, which contains the DNA genome and is, in turn, surrounded by a proteinaceous tegument layer and a lipid envelope. In herpes simplex virus, the interaction between the capsid and tegument is limited to the capsid vertices and involves two minor capsid proteins, pUL17 and pUL25, and the large inner tegument protein pUL36. pUL17 and pUL25 form a heterodimeric structure, the capsid vertex-specific component (CVSC), that lies on top of the peripentonal triplexes, while pUL36 has been reported to connect the CVSC to the penton. In this study, we used virus mutants with deletions in the genes for pUL36 and another inner tegument protein, pUL37, to analyze the contributions of these proteins to CVSC structure. Using electron cryomicroscopy and icosahedral reconstruction of mutants that express pUL17 and pUL25 but not pUL36, we showed that in contrast to accepted models, the CVSC is not formed from pUL17 and pUL25 on their own but requires a contribution from pUL36. In addition, the presence of full-length pUL36 results in weak density that extends the CVSC toward the penton, suggesting either that this extra density is formed directly by pUL36 or that pUL36 stabilizes other components of the vertex-tegument interface.ImportanceHerpesviruses have complex particles that are formed as a result of a carefully controlled sequence of assembly steps. The nature of the interaction between two of the major particle compartments, the icosahedral capsid and the amorphous tegument, has been extensively studied, but the identity of the interacting proteins and their roles in forming the connections are still unclear. In this study, we used electron microscopy and three-dimensional reconstruction to analyze virus particles formed by mutants that do not express particular interacting proteins. We show that the largest viral protein, pUL36, which occupies the layer of tegument closest to the capsid, is essential for formation of structurally normal connections to the capsid. This demonstrates the importance of pUL36 in the initial stages of tegument addition and provides new insights into the process of virus particle assembly.

Project description:The herpesvirus capsid assembles in the nucleus as an immature procapsid precursor built around viral scaffold proteins. The event that initiates procapsid maturation is unknown, but it is dependent upon activation of the VP24 internal protease. Scaffold cleavage triggers angularization of the shell and its decoration with the VP26 and pUL25 capsid-surface proteins. In both the procapsid and mature angularized capsid, the apical region of the major capsid protein (VP5) is surface exposed. We investigated whether the VP5 apical region contributes to intracellular transport dynamics following entry into primary sensory neurons and also tested the hypothesis that conserved negatively charged amino acids in the apical region contribute to VP26 acquisition. To our surprise, neither hypothesis proved true. Instead, mutation of glutamic acid residues in the apical region delayed viral propagation and induced focal capsid accumulations in nuclei. Examination of capsid morphogenesis based on epitope unmasking, capsid composition, and ultrastructural analysis indicated that these clusters consisted of procapsids. The results demonstrate that, in addition to established events that occur inside the capsid, the exterior capsid shell promotes capsid morphogenesis and maturation.IMPORTANCE Herpesviruses assemble capsids and encapsidate their genomes by a process that is unlike those of other mammalian viruses but is similar to those of some bacteriophage. Many important aspects of herpesvirus morphogenesis remain enigmatic, including how the capsid shell matures into a stable angularized configuration. Capsid maturation is triggered by activation of a protease that cleaves an internal protein scaffold. We report on the fortuitous discovery that a region of the major capsid protein that is exposed on the outer surface of the capsid also contributes to capsid maturation, demonstrating that the morphogenesis of the capsid shell from its procapsid precursor to the mature angularized form is dependent upon internal and external components of the megastructure.

Project description:The initial goal of this study was to reexamine the requirement of UL21 for herpes simplex virus 1 (HSV-1) replication. Previous studies suggested that UL21 is dispensable for replication in cell cultures, but a recent report on HSV-2 challenges those findings. As was done for the HSV-2 study, a UL21-null virus was made and propagated on complementing cells to discourage selection of compensating mutations. This HSV-1 mutant was able to replicate in noncomplementing cells, even at a low multiplicity of infection (MOI), though a reduction in titer was observed. Also, increased proportions of empty capsids were observed in the cytoplasm, suggesting a role for UL21 in preventing their exit from the nucleus. Surprisingly, passage of the null mutant resulted in rapid outgrowth of syncytial (Syn) variants. This was unexpected because UL21 has been shown to be required for the Syn phenotype. However, earlier experiments made use of only the A855V syncytial mutant of glycoprotein B (gB), and the Syn phenotype can also be produced by substitutions in glycoprotein K (gK), UL20, and UL24. Sequencing of the syncytial variants revealed mutations in the gK locus, but UL21 was shown to be dispensable for UL20Syn and UL24Syn To test whether UL21 is needed only for the A855V mutant, additional gBSyn derivatives were examined in the context of the null virus, and all produced lytic rather than syncytial sites of infection. Thus, UL21 is required only for the gBSyn phenotype. This is the first example of a differential requirement for a viral protein across the four syn loci.IMPORTANCE UL21 is conserved among alphaherpesviruses, but its role is poorly understood. This study shows that HSV-1 can replicate without UL21, although the virus titers are greatly reduced. The null virus had greater proportions of empty (DNA-less) capsids in the cytoplasm of infected cells, suggesting that UL21 may play a role in retaining them in the nucleus. This is consistent with reports showing UL21 to be capsid associated and localized to the nuclei of infected cells. UL21 also appears to be needed for viral membrane activities. It was found to be required for virus-mediated cell fusion, but only for mutants that harbor syncytial mutations in gB (not variants of gK, UL20, or UL24). The machinery needed for syncytial formation is similar to that needed for direct spread of the virus through cell junctions, and these studies show that UL21 is required for cell-to-cell spread even in the absence of syncytial mutations.

Dataset Information

The capsid protein encoded by U(L)17 of herpes simplex virus 1 interacts with tegument protein VP13/14.

Publications

The capsid protein encoded by U(L)17 of herpes simplex virus 1 interacts with tegument protein VP13/14.

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