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Kato SEM, Strahl AL, Moussatche N, Condit RC. Temperature-sensitive mutants in the vaccinia virus 4b virion structural protein assemble malformed, transcriptionally inactive intracellular mature virions. Virology 2005; 330:127-46. [PMID: 15527840 DOI: 10.1016/j.virol.2004.08.038] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2004] [Revised: 07/30/2004] [Accepted: 08/20/2004] [Indexed: 11/23/2022]
Abstract
Two noncomplementing vaccinia virus temperature-sensitive mutants, Cts8 and Cts26, were mapped to the A3L gene, which encodes the major virion structural protein, 4b. The two ts mutants display normal patterns of gene expression, DNA replication, telomere resolution, and protein processing during infection. Morphogenesis during mutant infections is normal through formation of immature virions with nucleoids (IVN) but appears to be defective in the transition from IVN to intracellular mature virus (IMV). In mutant infections, aberrant particles that have the appearance of malformed IMV accumulate. The mutant particles are wrapped in Golgi-derived membranes and exported from cells. Purified mutant particles are indistinguishable from wt particles in protein and DNA composition; however, they are defective in a permeabilized-virion-directed transcription reaction despite containing significant (Cts8) or even normal (Cts26) levels of specific transcription enzymes. These results indicate that the 4b protein is required for proper metamorphosis of IMV from IVN and that proper organization of the IMV structure is required to produce a transcriptionally active virion particle.
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Affiliation(s)
- Sayuri E M Kato
- Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL 32610, USA
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52
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Byrd CM, Hruby DE. A conditional-lethal vaccinia virus mutant demonstrates that the I7L gene product is required for virion morphogenesis. Virol J 2005; 2:4. [PMID: 15701171 PMCID: PMC548685 DOI: 10.1186/1743-422x-2-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Accepted: 02/08/2005] [Indexed: 11/12/2022] Open
Abstract
A conditional-lethal recombinant virus was constructed in which the expression of the vaccinia virus I7L gene is under the control of the tetracycline operator/repressor system. In the absence of I7L expression, processing of the major VV core proteins is inhibited and electron microscopy reveals defects in virion morphogenesis subsequent to the formation of immature virion particles but prior to core condensation. Plasmid-borne I7L is capable of rescuing the growth of this virus and rescue is optimal when the I7L gene is expressed using the authentic I7L promoter. Taken together, these data suggest that correct temporal expression of the VV I7L cysteine proteinase is required for core protein maturation, virion assembly and production of infectious progeny.
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Affiliation(s)
- Chelsea M Byrd
- Molecular and Cellular Biology Program, Oregon State University, 220 Nash Hall, Corvallis, Oregon, 97331 USA
| | - Dennis E Hruby
- Molecular and Cellular Biology Program, Oregon State University, 220 Nash Hall, Corvallis, Oregon, 97331 USA
- Department of Microbiology, Oregon State University, 220 Nash Hall, Corvallis, Oregon, 97331
USA
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53
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Byrd CM, Bolken TC, Mjalli AM, Arimilli MN, Andrews RC, Rothlein R, Andrea T, Rao M, Owens KL, Hruby DE. New class of orthopoxvirus antiviral drugs that block viral maturation. J Virol 2004; 78:12147-56. [PMID: 15507601 PMCID: PMC525040 DOI: 10.1128/jvi.78.22.12147-12156.2004] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2004] [Accepted: 07/09/2004] [Indexed: 11/20/2022] Open
Abstract
By using a homology-based bioinformatics approach, a structural model of the vaccinia virus (VV) I7L proteinase was developed. A unique chemical library of approximately 51,000 compounds was computationally queried to identify potential active site inhibitors. The resulting biased subset of compounds was assayed for both toxicity and the ability to inhibit the growth of VV in tissue culture cells. A family of chemotypically related compounds was found which exhibits selective activity against orthopoxviruses, inhibiting VV with 50% inhibitory concentrations of 3 to 12 microM. These compounds exhibited no significant cytotoxicity in the four cell lines tested and did not inhibit the growth of other organisms such as Saccharomyces cerevisiae, Pseudomonas aeruginosa, adenovirus, or encephalomyocarditis virus. Phenotypic analyses of virus-infected cells were conducted in the presence of active compounds to verify that the correct biochemical step (I7L-mediated core protein processing) was being inhibited. Electron microscopy of compound-treated VV-infected cells indicated a block in morphogenesis. Compound-resistant viruses were generated and resistance was mapped to the I7L open reading frame. Transient expression with the mutant I7L gene rescued the ability of wild-type virus to replicate in the presence of compound, indicating that this is the only gene necessary for resistance. This novel class of inhibitors has potential for development as an efficient antiviral drug against pathogenic orthopoxviruses, including smallpox.
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Affiliation(s)
- Chelsea M Byrd
- Department of Microbiology, 220 Nash Hall, Oregon State University, Corvallis, OR 97331, USA
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54
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da Fonseca FG, Weisberg AS, Caeiro MF, Moss B. Vaccinia virus mutants with alanine substitutions in the conserved G5R gene fail to initiate morphogenesis at the nonpermissive temperature. J Virol 2004; 78:10238-48. [PMID: 15367589 PMCID: PMC516429 DOI: 10.1128/jvi.78.19.10238-10248.2004] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The initial characterization of the product of the vaccinia virus G5R gene, which is conserved in all poxviruses sequenced to date, is described. The G5 protein was detected in the core fraction of purified virions, and transcription and translation of the G5R open reading frame occurred early in infection, independently of DNA replication. Attempts to delete the G5R gene and isolate a replication-competent virus were unsuccessful, suggesting that G5R encodes an essential function. We engineered vaccinia virus mutants with clusters of charged amino acids changed to alanines and determined that several were unable to replicate at 40 degrees C but grew well at 37 degrees C. At the nonpermissive temperature, viral gene expression and DNA replication and processing were unperturbed. However, tyrosine phosphorylation and proteolytic cleavage of the A17 membrane protein and proteolytic cleavage of core proteins were inhibited at 40 degrees C, suggesting an assembly defect. The cytoplasm of cells that had been infected at the nonpermissive temperature contained large granular areas devoid of cellular organelles or virus structures except for occasional short crescent-shaped membranes and electron-dense lacy structures. The temperature-sensitive phenotype of the G5R mutants closely resembled the phenotypes of vaccinia virus mutants carrying conditionally lethal F10R protein kinase and H5R mutations. F10, although required for phosphorylation of A17 and viral membrane formation, was synthesized by the G5R mutants under nonpermissive conditions. An intriguing possibility is that G5 participates in the formation of viral membranes, a poorly understood event in poxvirus assembly.
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Affiliation(s)
- Flavio G da Fonseca
- Laboratory of Viral Diseases, National Institutes of Health, 4 Center Dr., MSC 0445, Bethesda, MD 20892-0445, USA
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55
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Hedengren-Olcott M, Byrd CM, Watson J, Hruby DE. The vaccinia virus G1L putative metalloproteinase is essential for viral replication in vivo. J Virol 2004; 78:9947-53. [PMID: 15331728 PMCID: PMC515008 DOI: 10.1128/jvi.78.18.9947-9953.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The function of the putative metalloproteinase encoded by the vaccinia virus G1L gene is unknown. To address this question, we have generated a vaccinia virus strain in which expression of the G1L gene is dependent on the addition of tetracycline (TET) when infection proceeds in a cell line expressing the tetracycline repressor. The vvtetOG1L virus replicated similarly to wild-type Western Reserve (WR) virus in these cells when TET was present but was arrested at a late stage in viral maturation in the absence of TET. This arrest resulted in the accumulation of 98.5% round immature virus particles compared to 6.9% at a similar time point when TET was present. Likewise, the titer of infectious virus progeny decreased by 98.9% +/- 0.97% when the vvtetOG1L virus was propagated in the absence of TET. Mutant virus replication was partially rescued by plasmid-encoded G1L, but not by G1L containing an HXXEH motif mutated to RXXQR. Modeling of G1L revealed a predicted structural similarity to the alpha-subunit of Saccharomyces cerevisiae mitochondrial processing peptidase (alpha-MPP). The HXXEH motif of G1L perfectly overlaps the HXXDR motif of alpha-MPP in this model. These results demonstrate that G1L is essential for virus maturation and suggest that G1L is a metalloproteinase with structural homology to alpha-MPP. However, no obvious effects on the expression and processing of the vaccinia virus major core proteins were observed in the G1L conditional mutant in the absence of TET compared to results for the TET and wild-type WR controls, suggesting that G1L activity is required after this step in viral morphogenesis.
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Affiliation(s)
- Marika Hedengren-Olcott
- Department of Microbiology, 220 Nash Hall, Oregon State University, Corvallis, OR 97331, USA
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56
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Ansarah-Sobrinho C, Moss B. Vaccinia virus G1 protein, a predicted metalloprotease, is essential for morphogenesis of infectious virions but not for cleavage of major core proteins. J Virol 2004; 78:6855-63. [PMID: 15194761 PMCID: PMC421688 DOI: 10.1128/jvi.78.13.6855-6863.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Genes encoding orthologs of the vaccinia virus G1 protein are present in all poxviruses for which sequence information is available, yet neither the role of the protein nor its requirement for virus replication is known. G1 was predicted to be involved in the cleavage of core proteins, based on a transfection study and the presence of an HXXEH motif found in a subset of metallopeptidases. In the present study, we engineered a recombinant vaccinia virus containing a single copy of the G1L gene with a C-terminal epitope tag that is stringently regulated by the Escherichia coli lac repressor. In the absence of inducer, expression of G1 was repressed and virus replication was inhibited. Rescue of infectious virus was achieved by expression of wild-type G1 in trans, but not when the putative protease active site residues histidine-41, glutamate-44, or histidine-45 were mutated. Nevertheless, the synthesis and proteolytic processing of major core and membrane proteins appeared unaffected under nonpermissive conditions, distinguishing the phenotype of the G1L mutant from one in which the gene encoding the I7 protease was repressed. Noninfectious virus particles, assembled in the absence of inducer, did not attain the oval shape or characteristic core structure of mature virions. The polypeptide composition of these particles, however, closely resembled that of wild-type virus. Full-length and shorter forms of the G1 protein were found in the core fraction of virus particles assembled in the presence of inducer, suggesting that G1 is processed by self-cleavage or by another protease.
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Affiliation(s)
- Camilo Ansarah-Sobrinho
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institues of Health, Bethesda, MD 20892-0445, USA
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57
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Ansarah-Sobrinho C, Moss B. Role of the I7 protein in proteolytic processing of vaccinia virus membrane and core components. J Virol 2004; 78:6335-43. [PMID: 15163727 PMCID: PMC416539 DOI: 10.1128/jvi.78.12.6335-6343.2004] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Certain core and membrane proteins of vaccinia virus undergo proteolytic cleavage at consensus AG/X sites. The processing of core proteins is coupled to morphogenesis and is inhibited by the drug rifampin, whereas processing of the A17 membrane protein occurs at an earlier stage of assembly and is unaffected by the drug. A temperature-sensitive mutant with a lesion in the I7L gene exhibits blocks in morphogenesis and in cleavage of core proteins. We found that the mutant also failed to cleave the A17 membrane protein. To further investigate the role of the putative I7 protease, we constructed a conditional lethal mutant in which the I7L gene was regulated by the Escherichia coli lac repressor. In the absence of an inducer, the synthesis of I7 was repressed, proteolytic processing of the A17 membrane protein and the L4 core protein was inhibited, and virus morphogenesis was blocked. Under these conditions, expression of the wild-type I7 protein in trans restored protein processing. In contrast, rescue did not occur when the putative protease active site residue histidine 241 or cysteine 328 of I7 was converted to alanine. The mutation of an authentic AG/A and an alternative AG/S motif of L4 prevented substrate cleavage. Similarly, when AG/X sites of A17 were mutated, I7-induced cleavages at the N and C termini failed to occur. In conclusion, we provide evidence that I7 is a viral protease that is required for AG/X-specific cleavages of viral membrane and core proteins, which occur at early and late stages of virus assembly, respectively.
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Affiliation(s)
- Camilo Ansarah-Sobrinho
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 4 Center Drive, MSC 0445, Bethesda, MD 20892-0445, USA
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58
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Abstract
The vaccinia virus I7L gene product is predicted to be a cysteine proteinase and is demonstrated in this study to be responsible for cleavage of each of the three major core protein precursors (P4a, P4b, and P25K) in vivo. Mutagenesis of the putative catalytic triad of I7L or of the cleavage sites in the core protein precursors inhibits processing. A truncated protein lost the ability to cleave the core protein precursors.
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Affiliation(s)
- Chelsea M Byrd
- Molecular and Cellular Biology Program. Department of Microbiology, Oregon State University, Corvallis, Oregon 97331, USA
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59
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Mercer J, Traktman P. Investigation of structural and functional motifs within the vaccinia virus A14 phosphoprotein, an essential component of the virion membrane. J Virol 2003; 77:8857-71. [PMID: 12885904 PMCID: PMC167248 DOI: 10.1128/jvi.77.16.8857-8871.2003] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously reported the construction and characterization of an inducible recombinant virus in which expression of the vaccinia virus membrane protein A14 is experimentally regulated using the tetracycline operator-repressor system. Repression of A14, which results in a 1,000-fold reduction in viral yield, leads to an early block in viral morphogenesis characterized by the accumulation of large virosomes, empty "crescents" that fail to contact these virosomes, and, most strikingly, large numbers of aberrant 25-nm vesicles. Here we report the establishment of a transient-complementation system for the structure-function analysis of A14. We have constructed numerous mutant alleles of A14 designed to identify and test the importance of key structural and sequence motifs within A14, including sites of posttranslational modification, such as glycosylation, phosphorylation, and dimerization. From these studies we have determined that robust complementation ability requires an intact N terminus and two regions flanking the first membrane-spanning domain of A14. We show that A14 is modified by N-linked glycosylation both in vitro and in vivo. However, only a minority of A14 molecules are glycosylated in vivo and these are not encapsidated. In this report we also identify the sole phosphorylated serine residue of A14 as lying within the NHS(85) motif that undergoes glycosylation. Additionally, we show that the Cys(71) residue is required for intermolecular disulfide bond formation and describe the properties of a virus expressing an allele of A14 that cannot form disulfide-linked dimers.
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Affiliation(s)
- Jason Mercer
- Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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60
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Alejo A, Andrés G, Salas ML. African Swine Fever virus proteinase is essential for core maturation and infectivity. J Virol 2003; 77:5571-7. [PMID: 12719549 PMCID: PMC154020 DOI: 10.1128/jvi.77.10.5571-5577.2003] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2002] [Accepted: 02/12/2003] [Indexed: 11/20/2022] Open
Abstract
African swine fever virus (ASFV) encodes two polyprotein precursors named pp220 and pp62 that are sequentially processed during viral infection, giving rise to six major structural proteins. These reside at the core shell, a matrix domain located between the endoplasmic reticulum-derived inner envelope and the DNA-containing nucleoid. Proteolytic processing of the polyprotein precursors is catalyzed by the viral proteinase pS273R, a cysteine proteinase that shares sequence similarity with the SUMO1-processing peptidases. We describe here the construction and characterization of an ASFV recombinant, vS273Ri, that inducibly expresses the ASFV proteinase. Using vS273Ri, we show that repression of proteinase expression inhibits polyprotein processing and strongly impairs infective virus production. Electron microscopic examination of vS273Ri-infected cells showed that inhibition of proteolytic processing leads to the assembly of defective icosahedral particles containing a noncentered electron-dense nucleoid surrounded by an abnormal core shell of irregular thickness. The analysis of purified extracellular defective particles revealed that they contain the unprocessed pp220 and pp62 precursors, as well as the major DNA-binding nucleoid proteins p10 and pA104R. Altogether, these results indicate that the proteolytic processing of the polyproteins is not required for their incorporation into the assembling particles nor for the incorporation of the DNA-containing nucleoid. Instead, the ASFV proteinase is involved in a late maturational step that is essential for proper core assembly and infectivity.
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Affiliation(s)
- Alí Alejo
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Facultad de Ciencias, Cantoblanco, 28049 Madrid, Spain
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61
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Rubio D, Alejo A, Rodríguez I, Salas ML. Polyprotein processing protease of African swine fever virus: purification and biochemical characterization. J Virol 2003; 77:4444-8. [PMID: 12634404 PMCID: PMC150643 DOI: 10.1128/jvi.77.7.4444-4448.2003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The purified recombinant African swine fever virus polyprotein processing protease cleaves the two GG-X sites in polyprotein pp62 with the same efficiency. Cleavage at the site that is first recognized in vivo is not a requisite for cleavage at the second site, suggesting the existence of mechanisms that control the ordered processing of the polyprotein during infection.
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Affiliation(s)
- Daniel Rubio
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Universidad Autónoma de Madrid, Cantoblanco, Spain
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