Identification, cloning, and expression of the major capsid protein gene of human herpesvirus 6.

DNA sequence analysis of part of the human herpesvirus 6 (HHV-6) genome led to the identification of an open reading frame with amino acid sequence homology to the major capsid proteins (MCP) of other HHVs. DIAGON analysis showed that the closest homology was with human cytomegalovirus. Plasmids were constructed which were shown to express the HHV-6 MCP as either the entire open reading frame or as portions of it, and the recombinant-produced proteins were used to raise antisera. The antisera were shown by immunofluorescence to react with HHV-6-infected lymphoblastoid cells and in Western blots with a 135-kilodalton protein specific to HHV-6-infected cells. The recombinant protein expressed from the entire HHV-6 MCP gene was detected only weakly in Western blot assays with normal HHV-6-positive human sera as a probe.     

Designing of the pp65 recombinant antigen of human cytomegalovirus and investigation of its immunochemical properties

The primary and secondary structures of the pp65 phosphoprotein of human cytomegalovirus coded by the UL83 gene were studied by the methods of computer-aided analysis. An immunodominant protein fragment with 3 antigenic determinant was detected. The UL83 fragment coding the selected region was amplified and cloned in bacterial expressing vector. The recombinant protein was obtained and purified. On the basis of ELISA findings it was acknowledged as possible to use the pp65 recombinant protein jointly with pp150 and p52 in the diagnosis of antibodies specific to human cytomegalovirus.     

Discovery of a second form of tripartite complex containing gH-gL of human herpesvirus 6 and observations on CD46

The human herpesvirus 6 (HHV-6) glycoprotein H (gH)-glycoprotein L (gL) complex associates with glycoprotein Q (gQ) (Y. Mori, P. Akkapaiboon, X. Yang, and K. Yamanishi, J. Virol. 77:2452-2458, 2003), and the gH-gL-gQ complex interacts with human CD46 (Y. Mori, X. Yang, P. Akkapaiboon, T. Okuno, and K. Yamanishi, J. Virol. 77:4992-4999, 2003). Here, we show that the HHV-6 U47 gene, which is a positional homolog of the human cytomegalovirus glycoprotein O (gO) gene, encodes a third component of the HHV-6 gH-gL-containing envelope complex. A monoclonal antibody (MAb) against the amino terminus of HHV-6 gO reacted in immunoblots with protein species migrating at 120 to 130 kDa and 74 to 80 kDa in lysates of HHV-6-infected cells and with a 74- to 80-kDa protein species in purified virions. The 80-kDa form of gO was coimmunoprecipitated with an anti-gH MAb, but an anti-gQ MAb, which coimmunoprecipitated gH, did not coprecipitate gO. Furthermore, the gH-gL-gO complex did not bind to human CD46, indicating that the complex was not a ligand for CD46. These findings suggested that the viral envelope contains at least two kinds of tripartite complexes, gH-gL-gQ and gH-gL-gO, and that the gH-gL-gO complex may play a role different from that of gH-gL-gQ during viral infection. This is the first report of two kinds of gH-gL complexes on the viral envelope in a member of the herpesvirus family.     

Characterization of Glycoprotein H and L of Human Herpesvirus 7

The genes encoding the glycoproteins H (gH) and L (gL) of human herpesvirus 7 (HHV-7) have been identified. The gH open reading frame (ORF) was 2,070 base pairs in length and encoded a predicted 690 amino-acid protein. The gH contained characteristics of a transmembrane glycoprotein including 10 consensus N-linked glycosylation sites, 12 cysteine residues, a potential amino-terminal signal sequence and a predicted transmembrane segment located near the carboxyl terminus. The gL ORF was 738 base pairs in length and encoded a predicted 246 amino-acid protein. Four possible N-glycosylation sites and 6 cysteine residues existed within gL. The predicted amino-acid sequences of the HHV-7 gH and human herpesvirus 6 variant A (HHV-6A) gH gene products exhibited 23.6% identity to each other, and those of the gL gene products had 26.0% identity. Upon in vitro translation of the gL gene, the addition of microsomal membranes resulted in two modified products with molecular weights of 32 kDa and 35 kDa from the unmodified initial translation product of 26 kDa. An amino-terminal portion of gH and the full length of gL were expressed as glutathione S-transferase fusion proteins, and these proteins were used to raise immune sera in mice. Lysates of cells infected with HHV-7 were subjected to immunoprecipitation analysis. Approximate molecular weights of 33, 37, 80 and 90 kDa polypeptides were immunoprecipitated with antibodies against the gH protein. Antibodies against the gL protein polypeptides with the same molecular weights were also precipitated, and were observed with the antibodies against the gH protein. These results suggest that HHV-7 gH and gL may form a heterodimeric complex with each other in HHV-7 infected cells, as has been reported for other herpesviruses.     

Identification and procaryotic expression of the gene coding for the highly immunogenic 28-kilodalton structural phosphoprotein (pp28) of human cytomegalovirus.

Human cytomegalovirus contains a structural polypeptide that is 28 kilodaltons in apparent molecular size and is reactive in Western blot (immunoblot) analysis with the majority of human sera. The gene coding for this polypeptide was mapped on the genome of human cytomegalovirus strain AD169. A monoclonal antibody specific for the 28-kilodalton polypeptide was used to screen a cDNA library constructed from poly(A)+ RNA of human cytomegalovirus-infected cells in the procaryotic expression vector lambda gt11. Hybridization of cDNA with cosmid and plasmid clones mapped the gene to the HindIII R fragment. The gene was transcribed into a late 1.3-kilobase RNA. The nucleotide sequence of the coding region was determined. Parts of the 28-kilodalton polypeptide were expressed in Escherichia coli as hybrid proteins fused to beta-galactosidase. In Western blots these proteins were recognized by human sera. Antibodies raised against the hybrid proteins reacted specifically with the viral antigen in immunoprecipitations and Western blots. In vitro phosphorylation of HCMV virions and immunoprecipitation showed that the 28-kilodalton polypeptide was phosphorylated.     

Primary biliary cirrhosis sera recognize not only gp210 but also proteins of the p62 complex bearing N-acetylglucosamine residues from rat liver nuclear envelope

We have recently observed reactivity of primary biliary cirrhosis (PBC) sera with several proteins bearing N-acetylglucosamine residues from rat liver nuclear envelopes. The aim of this study was to characterize the reactive antigens. Sera from 31 patients with PBC, 30 with rheumatoid arthritis (RA) and 30 with Sjögren's syndrome (SS) were examined. Rim-like immunofluorescence staining was observed in 15 of 31 (48%) sera from patients with PBC, in 1 of 30 with RA and in 1 of 30 with SS. Upon immunoblotting using preparations of whole rat liver nuclear envelopes and their Triton X 100-KCl extract as antigen souces, a 200 kDa protein band was observed in 9 of sera with PBC. Furthermore, upon immunoblotting using the wheat germ aggulutinin-bound fraction of rat liver envelope as antigen, 62, 60 and 54 kDa protein bands corresponding to components of the p62 complex in the nuclear pore complex (Kita et al. Biochem. 113, 377–382) were observed in 7, 5 and 6 samples respectively, of the 31 PBC sera. Our data suggest that PBC sera recognize not only the 210 kDa protein but also the p62 complex proteins.Abbreviations ANA antinuclear antibody - AMA anti-mitochondrial antibodies - IF immunofluorescence - LAP2 lamina-associated polypeptide 2 - LBR lamin B receptor - anti-NBP 60 anti-nuclear localization signal binding protein 60 - NE nuclear envelope - NPC nuclear pore complex - PBC primary biliary cirrhosis - RA rheumatoid arthritis - SLE systemic lupus erythematosus - SS Sjögren's syndrome - WGA wheat germ agglutinin     

Nucleotide sequence analysis of a 38.5-kilobase-pair region of the genome of human herpesvirus 6 encoding human cytomegalovirus immediate-early gene homologs and transactivating functions.

Human herpesvirus 6 (HHV-6) is prevalent in the human population, with primary infection occurring early in life. Its predominant CD4+ T-lymphocyte tropism, its ability to activate human immunodeficiency virus type 1 (HIV-1) gene expression in vitro, and its upregulation of CD4 expression has led to speculation that HHV-6 may act as a positive cofactor in the progression of HIV infection to AIDS in individuals infected with both viruses. Previous sequencing studies of restricted regions of the 161.5-kbp genome of HHV-6 have demonstrated unequivocally that it is a member of the betaherpesvirus subgroup and have indicated that the HHV-6 genome is generally collinear with the unique long (UL) component of human cytomegalovirus (HCMV). In the work described in this report we have extended these sequencing studies by determining the primary structure of 38.5-kbp of the HHV-6 genome (genomic position 21.0 to 59.5 kbp). Within the sequenced region lie 31 open reading frames, 20 of which are homologous to positional counterparts in HCMV. Of particular significance is the identification of homologs of the HCMV UL36-38 and US22-type genes, which have been shown to encode transactivating proteins. We show that DNA sequences encoding these HHV-6 homologs were able to transactivate HIV-1 long terminal repeat-directed chloramphenicol acetyltransferase expression in cotransfection assays, thus demonstrating functional as well as structural conservation of these betaherpesvirus-specific gene products. Our data therefore confirm the close relationship between HHV-6 and HCMV and identify putative immediate-early regulatory genes of HHV-6 likely to play key roles in lytic replication and possibly also in the interactions between HHV-6 and HIV in dually infected cells.     

Human herpesvirus 6 is closely related to human cytomegalovirus.

A sequence of 21,858 base pairs from the genome of human herpesvirus 6 (HHV-6) strain U1102 is presented. The sequence has a mean composition of 41% G + C, and the observed frequency of CpG dinucleotides is close to that predicted from this mononucleotide composition. The sequence contains 17 complete open reading frames (ORFs) and part of another at the 5' end of the sequence. The predicted protein products of two of these ORFs have no recognizable homologs in the genomes of other sequenced human herpesviruses (i.e., Epstein-Barr virus [EBV], human cytomegalovirus [HCMV], herpes simplex virus [HSV], and varicella-zoster virus [VZV]). However, the products of nine other ORFs are clearly homologous to a set of genes that is conserved in all other sequenced herpesviruses, including homologs of the alkaline exonuclease, the phosphotransferase, the spliced ORF, and the major capsid protein genes. Measurements of similarity between these homologous sequences showed that HHV-6 is clearly most closely related to HCMV. The degree of relatedness between HHV-6 and HCMV was commensurate with that observed in comparisons between HSV and VZV or EBV and herpesvirus saimiri and significantly greater than its relatedness to EBV, HSV, or VZV. In addition, the gene for the major capsid protein and its 5' neighbor are reoriented with respect to the spliced ORFs in the genomes of both HHV-6 and HCMV relative to the organization observed in EBV, HSV, and VZV. Three ORFs in HHV-6 have recognizable homologs only in the genome of HCMV. Despite differences in gross composition and size, we conclude that the genomes of HHV-6 and HCMV are closely related.     

Expression of bovine leukemia virus protein p24 in Escherichia coli and its use in the immunoblotting assay.

The gag gene encoded protein, p24 of bovine leukemia virus (BLV), was cloned and expressed as thioredoxin-6xHis-p24 protein in Escherichia coli. The bacterial cells carrying plasmid pT7THis-p24 expressed the protein of 38 kDa that was detected by immunoblotting analysis using anti-p24 monoclonal antibodies and sera from BLV infected cattle and sheep. The purified p24 fusion protein was shown to be sensitive and specific for detection of BLV antibodies in the infected cattle.     

Characterization of G25K, a GTP-binding protein containing a novel putative nucleotide binding domain

Amino acid sequences were obtained for four peptides (p1, -2, -3 and 4) generated by chemical or proteolytic cleavage of a 25 kDa GTP-binding protein purified from human placental and platelet membranes. The peptides shared sequence similarities with those contained in several of the ras-related GTP-binding proteins. Peptide p2, a 12-mer, was homologous with a region of the GTP-binding proteins that contains a structural motif proposed to contribute to the nucleotide binding site. However, whereas nearly all GTP-binding proteins exhibit the residues NKXD as this motif, p2 contains TQID. Antisera (Ap1 and Ap3) raised against synthetic peptides corresponding to p1 and p3 specifically reacted on Western blots with the 25 kDa GTP-binding protein purified from human placenta, human platelet and bovine brain as well as with a 25 kDa polypeptide in various cell lines. These results demonstrate the widespread existence of an abundant 25 kDa GTP-binding protein which contains a putative nucleotide binding domain that is chemically distinct from that described for all GTP-binding proteins of known primary structure.     

Direct Repeat 6 from Human Herpesvirus-6B Encodes a Nuclear Protein that Forms a Complex with the Viral DNA Processivity Factor p41

The SalI-L fragment from human herpesvirus 6A (HHV-6A) encodes a protein DR7 that has been reported to produce fibrosarcomas when injected into nude mice, to transform NIH3T3 cells, and to interact with and inhibit the function of p53. The homologous gene in HHV-6B is dr6. Since p53 is deregulated in both HHV-6A and -6B, we characterized the expression of dr6 mRNA and the localization of the translated protein during HHV-6B infection of HCT116 cells. Expression of mRNA from dr6 was inhibited by cycloheximide and partly by phosphonoacetic acid, a known characteristic of herpesvirus early/late genes. DR6 could be detected as a nuclear protein at 24 hpi and accumulated to high levels at 48 and 72 hpi. DR6 located in dots resembling viral replication compartments. Furthermore, a novel interaction between DR6 and the viral DNA processivity factor, p41, could be detected by confocal microscopy and by co-immunoprecipitation analysis. In contrast, DR6 and p53 were found at distinct subcellular locations. Together, our data imply a novel function of DR6 during HHV-6B replication.     

Human herpesvirus 6A U27 plays an essential role for the virus propagation

Human herpesvirus 6A (HHV-6A) is a member of the genus Roseolovirus and the subfamily Betaherpesvirinae. It is similar to and human cytomegalovirus (HCMV). HHV-6A encodes a 41 kDa nuclear phosphoprotein, U27, which acts as a processivity factor in the replication of the viral DNA. HHV-6A U27 has 43% amino acid sequence homology with HCMV UL44, which is important for DNA replication. A previous study on HHV-6A U27 revealed that it greatly increases the in vitro DNA synthesis activity of HHV-6A DNA polymerase. However, the role of U27 during the HHV-6A virus replication process remains unclear. In this study, we constructed a U27-deficient HHV-6A mutant (HHV-6ABACU27mut) with a frameshift insertion at the U27 gene using an HHV-6A bacterial artificial chromosome (BAC) system. Viral reconstitution from the mutant BAC DNA was not detected, in contrast to the wild type and the revertant from the U27 mutant. This suggests that U27 plays a critical role in the life cycle of HHV-6A.     

Gastric parietal cell antigens of 60-90, 92, and 100-120 kDa associated with autoimmune gastritis and pernicious anemia. Role of N-glycans in the structure and antigenicity of the 60-90-kDa component

Thirty-four human sera containing parietal cell autoantibodies (PCA) specifically immunoprecipitated two antigens, with apparent molecular masses of 60-90 kDa and 100-120 kDa under nonreducing conditions and 60-90 kDa and 120-150 kDa under reducing conditions, from porcine gastric membrane extracts. A third antigen of 92 kDa was only observed in immunoprecipitates analyzed under reducing conditions. By immunoblotting, 24 of the 34 PCA-positive sera reacted with only the 60-90-kDa antigen, three reacted with a broad 60-120-kDa smear, one reacted only with a 92-kDa antigen and six did not react. Reactivity with the 60-90-kDa antigen was observed with gastric membranes from dog, pig, rat, and rabbit. Twenty PCA-negative sera did not react with these components by immunoprecipitation or immunoblotting. PCA reactivity with the 60-90-kDa antigen was abolished when the gastric membranes were (a) digested with Pronase, (b) reduced with 100 mM dithiothreitol, (c) treated with sodium periodate, or (d) digested with N-glycanase. The 60-90-kDa and 100-120-kDa components were insensitive to neuraminidase treatment. N-glycanase digestion of 125I-labeled antigens purified by immunoprecipitation and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis collapsed the 60-90-kDa antigen to a sharp 34-kDa band; the 100-120-kDa component was unaffected. These observations suggest that (i) parietal cell antigens comprise three components of 60-90, 92, and 100-120 kDa; (ii) the epitopes differ in conformational sensitivity; (iii) the 60-90-kDa antigen is a conserved molecule comprising a 34-kDa core protein extensively glycosylated with N-linked oligosaccharides; (iv) sialic acid residues are not present in the 60-90- and 100-120-kDa molecules, and (v) the carbohydrate and protein moieties of the 60-90-kDa molecule are required for antibody binding.     

Identification of the human herpesvirus 6 glycoprotein H and putative large tegument protein genes.

Determination of the nucleotide sequences of two molecular clones of human herpesvirus 6 (HHV-6) (strain GS) and comparison with those of human cytomegalovirus (HCMV) has allowed the identification of the genes for the glycoprotein H (gH) and the putative large tegument protein of HHV-6. Two molecular clones of fragments of HHV-6, the BamHI-G fragment (7,981 bp) of the clone termed pZVB43 and a HindIII fragment (8,717 bp) of the clone termed pZVH14, represent approximately 10% of the HHV-6 genome (16,689). An open reading frame within the BamHI-G fragment was designated the gH gene of HHV-6 because of the extensive sequence similarity of its predicted product (79,549 Da) to the HCMV gH gene product. The predicted product (239,589 Da) of an open reading frame within clone pZVH14 showed homology to the predicted product of the proposed gene of HCMV representing the large tegument protein. Computer analyses indicated a closer relationship of the predicted peptides of these HHV-6 genes to those of HCMV than to those of the other human herpesviruses Epstein-Barr virus, herpes simplex virus type 1, and varicella-zoster virus. The gH gene was more conserved among the human herpesvirus group, while significant sequence similarity of the tegument gene could be found only with that of HCMV. The data reported here with one conserved gene (gH) and a more divergent gene (tegument) support previous reports that HHV-6 and HCMV are more closely related to each other than to the other well-characterized human herpesviruses.     

Identification and analysis of a novel heparin-binding glycoprotein encoded by human herpesvirus 7

Human herpesvirus 6 (HHV-6) and HHV-7 are closely related betaherpesviruses that encode a number of genes with no known counterparts in other herpesviruses. The product of one such gene is the HHV-6 glycoprotein gp82-105, which is a major virion component and a target for neutralizing antibodies. A 1.7-kb cDNA clone from HHV-7 was identified which contains a large open reading frame capable of encoding a predicted primary translational product of 468 amino acids (54 kDa) with 13 cysteine residues and 9 potential N-linked glycosylation sites. This putative protein, which we have termed gp65, was homologous to HHV-6 gp105 (30% identity) and contained a single potential membrane-spanning domain located near its amino terminus. Comparison of the cDNA sequence with that of the viral genome revealed that the gene encoding gp65 contains eight exons, spanning almost 6 kb of the viral genome at the right (3') end of the HHV-7 genome. Northern (RNA) blot analysis with poly(A)(+) RNA from HHV-7-infected cells revealed that the cDNA insert hybridized to a single major RNA species of 1.7 kb. Antiserum raised against a purified, recombinant form of gp65 recognized a protein of roughly 65 kDa in sucrose density gradient-purified HHV-7 preparations; treatment with PNGase F reduced this glycoprotein to a putative precursor of approximately 50 kDa. Gp65-specific antiserum also neutralized the infectivity of HHV-7, while matched preimmune serum did not do so. Finally, analysis of the biochemical properties of recombinant gp65 revealed a specific interaction with heparin and heparan sulfate proteoglycans and not with closely related molecules such as N-acetylheparin and de-N-sulfated heparin. At least two domains of the protein were found to contribute to heparin binding. Taken together, these findings suggest that HHV-7 gp65 may contribute to viral attachment to cell surface proteoglycans.     

Identification of proteins specific for human herpesvirus 6-infected human T cells.

Proteins specific for human herpesvirus 6 (HHV-6)-infected human T cells (HSB-2) were examined by using polyclonal rabbit antibodies and monoclonal antibodies against HHV-6-infected cells and human sera. More than 20 proteins and six glycoproteins specific for HHV-6-infected cells were identified from [35S]methionine- and [3H]glucosamine-labeled total-cell extracts. Polyclonal rabbit antibodies immunoprecipitated 33 [35S]methionine-labeled HHV-6-specific polypeptides with approximate molecular weights ranging from 180,000 to 31,000. In immunoprecipitation and Western immunoblot reactions, a patient's serum also recognized more than 30 HHV-6-specific proteins and seven glycoproteins. In contrast, sera from individuals with high-titered antibodies against other human herpesviruses reacted with fewer HHV-6-infected cell proteins, and only a 135,000-Mr polypeptide was prominent. Monoclonal antibodies to HHV-6-infected cells reacted with single and multiple polypeptides specific for virus-infected cells and immunoprecipitated three distinct sets of glycoproteins, which were designated gp105k and gp82k, gp116k, gp64k, and gp54k, and gp102k.