Phylogenetic analyses of virus isolates in the genus Hantavirus, family Bunyaviridae

We constructed a phylogenic tree by pairwise comparison of the deduced amino acid sequences encoded in the medium (M) genome segments of 13 hantaviruses. Five distinct branches were identified, four of which are represented by Hantaan, Seoul, Puumala, and Prospect Hill viruses. These groups corresponded to those previously established by serological and genetic means. In addition, we present sequence information for the M segment of Thailand virus and demonstrate that it represents a unique, fifth branch on the dendrogram. We show that a tree nearly identical to that constructed from the deduced amino acids encoded in the M segments of these viruses can be constructed by comparing nucleotide sequences of a 333-bp region of the M segments of the same hantaviruses. This region can be amplified, for most hantaviruses, by reverse transcriptase-polymerase chain reaction (RT-PCR) techniques, using a single primer pair. By using this method, we constructed a consensus tree for 30 hantaviruses, including 15 isolates for which we PCR-amplified and sequenced the 333-bp region. In addition to the five branches described above, we identified a sixth unique hantavirus group represented by Dobrava virus, an Apodemus isolate from Slovenia. Although we were unable to PCR-amplify the M segment of Thottapalayam virus, a distantly related hantavirus isolated from a shrew captured in India, we were able to amplify, clone, and sequence a portion of the small (S) segment of that virus. When we compared our Thottapalayam sequence to corresponding S segment sequences of other hantaviruses, the results indicated that this virus may represent a seventh, distinct group of hantaviruses.

Epitope mapping studies with neutralizing and non-neutralizing monoclonal antibodies to the G1 and G2 envelope glycoproteins of Hantaan virus

Epitopes recognized by three G1-specific and two G2-specific neutralizing monoclonal antibodies to Hantaan virus were mapped by sequence analyses of the complete M genome segments of neutralization escape variant viruses. For each variant, we detected nucleotide sequence substitutions which resulted in a single amino acid change in either the G1 or G2 protein. Serological properties of the variant viruses correlated with changes identified by nucleotide sequence analyses. To map epitopes recognized by three G1-specific and six G2-specific, non-neutralizing monoclonal antibodies, we prepared genes, truncated at the carboxy terminal coding regions of G1 or G2, and expressed them with baculovirus recombinants or transiently in a vaccinia/T7 RNA polymerase system. Reactivities of the monoclonal antibodies with the truncated proteins were monitored by immune precipitation of the radiolabeled, truncated glycoproteins. We determined that all three of the G1-specific antibodies reacted with truncated proteins, which retained the amino terminal one-third of G1, but lost reactivity with shorter G1 proteins. The G2-specific antibodies only recognized G2 proteins, which retained approximately 80% of the G2 gene.

Nucleotide and deduced amino acid sequences of the M and S genome segments of two Puumala virus isolates from Russia

Hemorrhagic fever with renal syndrome (HFRS) is caused by viruses in the Hantavirus genus, family Bunyaviridae. Three serologically distinct hantaviruses, Hantaan, Seoul and Puumala viruses, are known to cause HFRS. We report here, for the first time, gene sequences of two human Puumala virus isolates, P360 and K27, obtained in an HFRS endemic region of the former Soviet Union. We compared the nucleotide sequences and the derived amino acid sequences of their gene products to a Puumala virus isolate from rodents.

Molecular and antigenic characterization of HV114, a hantavirus isolated from a patient with haemorrhagic fever with renal syndrome in China

The relationship of a Hantaan-like virus (HV114), isolated from a patient with haemorrhagic fever with renal syndrome in Hubei Province, People's Republic of China, to other pathogenic hantaviruses was evaluated by cross-neutralization studies and nucleotide sequence analysis of the M genome segment. Plaque reduction neutralization assays indicated that HV114 is closely related to prototype Hantaan (HTN) virus, strain 76-118, which was originally isolated from an Apodemus field mouse in Korea. Comparison of the M genome segments of HTN 76-118 and HV114 revealed sequence identity of 84.7% and 95.4% for nucleotides and deduced amino acids, respectively. These data demonstrate that HV114 and 76-118 are two closely related but different isolates of HTN virus, establishing the scientific basis for testing and future use in China of a recombinant vaccine expressing the genome of HTN virus strain 76-118.

Expression of non-conserved regions of the S genome segments of three hantaviruses: evaluation of the expressed polypeptides for diagnosis of haemorrhagic fever with renal syndrome

Haemorrhagic fever with renal syndrome (HFRS) is a serious and often fatal disease caused by viruses in the Hantavirus genus of the family Bunyaviridae. We expressed the entire coding region of the small (S) genome segments of three serologically distinct hantaviruses as soluble proteins in Escherichia coli and evaluated the expressed nucleocapsid proteins (NPs) as antigens for diagnosis of HFRS. We also prepared novel diagnostic antigens by expressing truncated genes from which we deleted amino acid coding regions that were highly conserved among the three viruses. These antigens were analysed for their potential to detect and differentiate between antisera to various hantaviruses by ELISA. ELISA results obtained with HFRS patient sera or with sera from naturally or experimentally infected animals indicate that homologous antigens and antisera reacted to high titre. The truncated NPs were more specific than the complete NPs in distinguishing between possible aetiological agents of HFRS. Our findings demonstrate that prokaryotic expression of portions of the NPs of specific hantaviruses can be used to generate, readily and efficiently, large quantities of antigen that is both sensitive and specific in diagnostic assays for HFRS.

Cloning and sequence analysis of the genes encoding the nonstructural proteins of Langat virus and comparative analysis with other flaviviruses

Langat virus, a member of the family Flaviviridae is antigenically very similar to highly pathogenic tick-borne encephalitis viruses. We cloned and sequenced the complete nonstructural gene-coding region of Langat virus (strain TP21) and compared the deduced amino acid sequences of each nonstructural protein to those of other flaviviruses. By alignment with the reported amino acid sequences of the nonstructural proteins of several flaviviruses, we were able to predict proteolytic cleavage sites and identify sequence motifs, which are highly conserved among flaviviruses. Sequence similarity calculations revealed that the NS3 and NS5 proteins are the most highly conserved of the flavivirus nonstructural proteins. The NS3 and NS5 proteins of Langat virus contained specific peptide sequences that have been demonstrated to be associated with helicase or polymerase activities, respectively. The NS1 protein of Langat virus displayed complete homology of potential N-linked glycosylation sites and cysteine residues with the NS1 proteins of other tick-borne flaviviruses, suggesting a highly conserved NS1 protein structure. The data presented in this report serve to complete the entire sequence of the Langat virus-coding region and provide the basis for comparison of this naturally attenuated virus to the other highly virulent tick-borne flaviviruses.

Preparation of candidate vaccinia-vectored vaccines for haemorrhagic fever with renal syndrome

Two vaccinia-vectored candidate vaccines for haemorrhagic fever with renal syndrome were prepared by inserting cDNA, representing the medium (M) genome segment, or the M and the small (S) genome segments of Hantaan virus into the thymidine kinase gene of the Connaught vaccine strain of vaccinia virus. In the single recombinant, the M segment was placed under control of the vaccinia virus 7.5 kDa promoter. In the double recombinant, the M and S segments were placed under control of the vaccinia virus 7.5 kDa and 11 kDa promoters, respectively. An immunoplaque assay technique was developed to select recombinants without the need for expression of irrelevant genes or use of potential mutagens. Proteins indistinguishable from authentic viral envelope glycoproteins and nucleocapsid protein were observed by immunoprecipitation with antibodies to Hantaan virus. The recombinant expressing both the M and the S segments was selected for further development and testing as a human vaccine.

Coexpression of the membrane glycoproteins G1 and G2 of Hantaan virus is required for targeting to the Golgi complex

To study the intracellular transport and targeting to the Golgi complex of the membrane glycoproteins G1 and G2 of Hantaan virus, we have expressed them together and separately using recombinant vaccinia viruses. When expressed from the same recombinant vaccinia virus, G1 and G2 were localized to the Golgi complex as analyzed by both immunofluorescence and subcellular fractionation. However, when the glycoproteins were expressed from separate recombinant viruses, both proteins remained in the endoplasmic reticulum. Using several monoclonal antibodies, it was found that G1 expressed alone did not acquire its correct conformation. Finally, if cells were coinfected with G1- and G2-expressing recombinant viruses, the proteins were again targeted to the Golgi complex. The N-linked glycans remained in all cases largely endoglycosidase-H sensitive. With none of the recombinant viruses were expression of the glycoproteins observed on the cell surface. Neither did chasing in the presence of cycloheximide result in the surface expression of G1 or G2. Our results indicate that for transport out of the endoplasmic reticulum and proper targeting to the Golgi complex, the two glycoproteins have to be coexpressed. The most likely interpretation is that G1 and G2 have to interact with each other in the endoplasmic reticulum in order to become transport competent.

Antigenic subunits of Hantaan virus expressed by baculovirus and vaccinia virus recombinants

Baculovirus and vaccinia virus vectors were used to express the small (S) and medium (M) genome segments of Hantaan virus. Expression of the complete S or M segments yielded proteins electrophoretically indistinguishable from Hantaan virus nucleocapsid protein or envelope glycoproteins (G1 and G2), and expression of portions of the M segment, encoding either G1 or G2 alone, similarly yielded proteins which closely resembled authentic Hantaan virus proteins. The expressed envelope proteins retained all antigenic sites defined by a panel of monoclonal antibodies to Hantaan virus G1 and G2 and elicited antibodies in animals which reacted with authentic viral proteins. A Hantaan virus infectivity challenge model in hamsters was used to assay induction of protective immunity by the recombinant-expressed proteins. Recombinants expressing both G1 and G2 induced higher titer antibody responses than those expressing only G1 or G2 and protected most animals from infection with Hantaan virus. Baculovirus recombinants expressing only nucleocapsid protein also appeared to protect some animals from challenge. Passively transferred neutralizing monoclonal antibodies similarly prevented infection, suggesting that an antibody response alone is sufficient for immunity to Hantaan virus.

Coding properties of the S and the M genome segments of Sapporo rat virus: comparison to other causative agents of hemorrhagic fever with renal syndrome

Three serologically distinct groups of hantaviruses have been associated with severe, moderate, and mild forms of hemorrhagic fever with renal syndrome (HFRS). To gain a better understanding of the genetic variation among these viruses, we cloned and sequenced the M and the S genome segments of Sapporo rat virus, an etiologic agent of moderate HFRS, and compared the predicted gene products to those of Hantaan virus, and the Hällnäs strain of Puumala virus, which are etiologic agents of severe and mild HFRS, respectively. The SR-11 S segment consisted of 1769 nucleotides and had an open reading frame (ORF) in the virus-complementary sense RNA with a coding capacity of 429 amino acids. Deduced amino acids from the SR-11 S segment ORF displayed 83% homology with those of Hantaan nucleocapsid (N) protein. Comparison of the S segment ORFs of all three viruses revealed 58% homology. No evidence for additional nonstructural protein(s) encoded by the SR-11 S segment was obtained. The SR-11 M segment consisted of 3651 nucleotides and had an ORF in the virus-complementary sense RNA with a coding capacity of 1134 amino acids. Amino acid sequences predicted from the SR-11 M segment ORF were 75% homologous with those encoding Hantaan G1 and G2 envelope glycoproteins. Comparison of the deduced amino acid sequences of the M segment ORFs of SR-11, Hantaan, and Hällnäs viruses revealed a 43% homology for amino acids constituting the G1 proteins and a 55% homology for amino acids constituting the G2 proteins of the three viruses. The envelope proteins of SR-11 virus were localized within the M segment ORF by amino-terminal sequence analysis of purified G1 and G2. G1 initiated at amino acid 17 and G2 at amino acid 647 within the ORF. Five potential asparagine-linked glycosylation sites were identified in the SR-11 G1 coding sequences, four of which were conserved between Hantaan and SR-11 viruses and three of which were conserved among all three viruses. One potential glycosylation site was identified in the SR-11 G2 coding sequences and was conserved among Hantaan, SR-11 and Hällnäs viruses. Cysteine residues were highly conserved within the M segment ORFs of all three viruses, suggesting a similar structure and function of the G1 and G2 proteins.

Expression of the Bacillus anthracis protective antigen gene by baculovirus and vaccinia virus recombinants

The gene encoding Bacillus anthracis protective antigen (PA) was modified by site-directed mutagenesis, subcloned into baculovirus and vaccinia virus plasmid transfer vectors (pAcYM1 and pSC-11, respectively), and inserted via homologous recombinations into baculovirus Autographa californica nuclear polyhedrosis virus or vaccinia virus (strains WR and Connaught). Expression of PA was detected in both systems by immunofluorescence assays with antisera from rabbits immunized with B. anthracis PA. Western blot (immunoblot) analysis showed that the expressed product of both systems was slightly larger (86 kilodaltons) than B. anthracis-produced PA (83.5 kilodaltons). Analysis of trypsin digests of virus-expressed and authentic PA suggested that the size difference was due to the presence of a signal sequence remaining with the virus-expressed protein. Immunization of mice with either recombinant baculovirus-infected Spodoptera frugiperda cells or with vaccinia virus recombinants elicited a high-titer, anti-PA antibody response.

Baculovirus expression of the M genome segment of Rift Valley fever virus and examination of antigenic and immunogenic properties of the expressed proteins

Autographa californica nuclear polyhedrosis viral recombinants containing coding information for the Rift Valley fever virus (RVFV) envelope glycoproteins (G1 and G2) and varying amounts of preglycoprotein coding sequences were prepared by using transfer vectors pAc373 or pAcYM1. Expression products were processed to yield proteins indistinguishable from authentic G1 and G2 by gel electrophoresis. The immunogenic properties of the expressed proteins were assessed by immunizing mice and challenging with RVFV. A single inoculation with lysates of cells infected with recombinants expressing both G1 and G2 induced neutralizing antibody responses in mice and protected them from an otherwise lethal challenge with RVFV. Lysates of cells infected with a recombinant expressing only G2 also induced a protective response after two immunizations. Survivors displayed elevated antibody titers to G1 and G2 and also developed antibodies to the RVFV nucleocapsid protein, the latter allowing discrimination from vaccinated mice and indicating that animals had survived infection. Nonimmune mice were protected from lethal RVFV infection by passive transfer of sera from animals immunized with recombinant antigens, indicating that a humoral immune response is sufficient to protect against RVFV.

Characterization of Hantaan virus envelope glycoprotein antigenic determinants defined by monoclonal antibodies

A panel of 24 monoclonal antibodies (MAbs) to the G1 or G2 envelope glycoproteins of Hantaan virus were used to determine the surface topography and functional properties of antigenic sites. Nine distinct, partially overlapping antigenic sites, two on G1 and seven on G2, were demonstrated by competitive binding assays. Analyses of the antigenic sites by haemagglutination (HA) inhibition and plaque-reduction neutralization tests showed that all of the sites, except one on G1, were related to viral HA. Only one of the G1 antigenic sites and two of the G2 sites were involved in virus neutralization. These results suggest that certain epitopes related to HA were not critical for virus neutralization. The nine antigenic sites could be further divided into 13 based upon the serological cross-reactivity of MAbs with viruses representative of each of the four known antigenic groups within the Hantavirus genus of Bunyaviridae, i.e. Hantaan, Seoul, Puumala and Prospect Hill viruses.

Conservation of antigenic properties and sequences encoding the envelope proteins of prototype Hantaan virus and two virus isolates from Korean haemorrhagic fever patients

Viruses isolated from the blood of two Korean haemorrhagic fever patients were propagated in cell culture and compared to prototype Hantaan virus which was isolated from Apodemus mice. The antigenic properties of the human isolates were found to be closely related to Hantaan virus by plaque reduction neutralization, haemagglutination inhibition and fluorescent antibody staining with both polyclonal and monoclonal antibodies. The medium genome segment of each human isolate was sequenced and compared to that of Hantaan virus. Nucleotides comprising the Hantaan virus G1 and G2 envelope protein-coding regions differed from those of the other viruses by only 5.4% and 5.7%. The human isolates differed from one another by 1.6%. The nucleotide differences resulted in predicted amino acid variations of 1.3% to 2.3% among the three viruses, with the majority occurring as conservative substitutions in G1.

Baculovirus expression of the small genome segment of Hantaan virus and potential use of the expressed nucleocapsid protein as a diagnostic antigen

Autographa californica nuclear polyhedrosis virus (AcNPV) was used as an expression vector for the nucleocapsid protein gene of Hantaan virus. Two different cDNA clones representing the small genome segment of Hantaan virus were inserted into the transfer vector pAcYM1, and recombinants were generated by replacement of a portion of the baculovirus polyhedrin gene with the foreign, Hantaan virus gene. Recombinants containing both the first and second ATG initiation codons of the Hantaan virus gene produced nucleocapsid protein, while those containing only the second codon did not. The expressed nucleocapsid protein was evaluated as a potential diagnostic antigen with a variety of hantavirus-immune sera. The high levels of expression obtained, specific serological reactivity with immune sera and the low level of biological containment required for production of this protein all suggest a significant advantage over authentic viral antigen for diagnosis of hantavirus infection.

Expression of the Hantaan virus M genome segment by using a vaccinia virus recombinant

A cDNA containing the complete open reading frame of the Hantaan virus (HTN) M genome segment has been cloned into vaccinia virus. This recombinant virus expresses two glycoproteins which are similar to the HTN structural glycoproteins, G1 and G2, in molecular weight, cleavage pattern, and cellular distribution. Both HTN and recombinant vaccinia virus glycoproteins are exclusively associated with the Golgi apparatus of the cell. Despite this intracellular restriction, mice inoculated with the recombinant vaccinia virus raised neutralizing antibodies against HTN. The specificity of virus neutralization appears to reside in the HTN glycoproteins, since a vaccinia virus recombinant expressing the HTN nucleocapsid protein was unable to elicit a neutralizing antibody response.

Detection of hantaviruses with RNA probes generated from recombinant DNA

Radiolabeled RNA probes generated from cDNA clones of the M and S genome segments of Hantaan virus readily detected Hantaan virus and two isolates from Korean hemorrhagic fever patients but were less effective in detecting four other hantaviruses.

Partial nucleotide sequence of the Japanese encephalitis virus genome

Approximately 10 kb of the estimated 10.9-kb genome of the Japanese encephalitis virus (JE; Nakayama strain) has been cloned as cDNA; the uncloned portion includes 430 bases at the 5'-terminus and 450 bases at the 3'-end. A map of the genome has been developed through nucleotide sequencing and in vivo expression with the Escherichia coli expression vector lambda gt11 and immunological identification. Sequence results for 4320 nucleotides suggest the JE genome organization is very similar to those of three other flaviviruses for which sequence information is available. Like the other flaviviruses, the JE proteins are encoded by a single open reading frame that continues uninterrupted throughout the region sequenced. Considerable homology exists between the JE RNA and protein sequences and those of the other characterized flaviviruses. Comparative nucleotide and (amino acid) homology values for the M-E-NS1-ns2 segment of JE are approximately MVE, 70% (80%), WN, 68% (76%), and YF, 50% (45%). Even greater homology is suggested when the protein hydrophobicity profiles are compared. The molecular relationships are consistent with the established serological relationships among JE, MVE, and WN viruses and argue that these flaviviruses may have been derived from a common evolutionary ancestor.

Hantaan virus M RNA: coding strategy, nucleotide sequence, and gene order

The M genome segment of Hantaan virus was molecularly cloned and the nucleotide sequence of cDNA was determined. The virion RNA is 3616 bases long with 3'- and 5'-terminal nucleotide sequences complementary for 18 bases. A single long open reading frame in the viral complementary-sense RNA had the potential to encode 1135 amino acids or a polypeptide of 126,000 Da. Amino-terminal sequences of isolated G1 and G2 envelope glycoproteins were determined, revealing a gene order with respect to message sense RNA of 5'-G1-G2-3'. Mature G1 begins 18 amino acids beyond the first AUG of the open reading frame, preceded by a short, hydrophobic leader sequence. G2 begins at the 649th amino acid of the open reading frame and also follows a hydrophobic sequence. Carboxy termini of G1 and G2 were localized and gene order was verified by immune precipitation of Hantaan proteins with antisera to synthetic peptides generated by using amino acid sequences derived from the cDNA sequence. The antipeptide sera were also reactive by immunoblotting with SDS-denatured G1 and G2. Molecular weights of 64,000 and 53,700 were calculated for the G1 and G2 glycoproteins, respectively, from their predicted amino acid sequences. Five potential asparagine-linked glycosylation sites were contained within the G1 amino acid sequence and two within the G2 sequence. These data are consistent with our previous estimates of the molecular weights and extent of glycosylation of the Hantaan envelope glycoproteins.

Coding strategy of the S genome segment of Hantaan virus

Hantaan virus is the type species of the recently recognized Hantavirus genus of Bunyaviridae. The small (S) RNA segment of the negative-sense, tripartite genome was molecularly cloned and the nucleotide sequence was determined. The RNA sequence derived from the cDNA copy was found to contain 1696 nucleotides. A single open reading frame of sufficient size to encode the virus nucleocapsid protein was detected in the cDNA corresponding to viral complementary-sense RNA. RNA transcripts of the cDNA were synthesized with SP6 polymerase and were used to program cell-free reticulocyte lysate translation systems. Viral complementary-sense transcripts served as efficient messages in translation systems and generated Hantaan nucleocapsid protein. No translation products were detected when lysates were programmed with viral-sense transcripts. This coding assignment of the nucleocapsid protein to the viral complementary-sense RNA of the S genome segment is consistent with those of other members of this family. Unlike other Bunyaviridae, which encode both a nucleocapsid protein and a nonstructural (NSs) protein of similar sizes, a NSs protein has not been identified for Hantaan virus. Furthermore, other than the nucleocapsid protein gene sequence, the only potential open reading frame in Hantaan S RNA encoded a short, 48-amino acid polypeptide which initiated two codons beyond the termination of the nucleocapsid protein in the same reading frame. These data demonstrate that the coding strategy of the Hantaan virus S RNA is different than those reported for other viruses in this family.

Hantaan virus replication: effects of monensin, tunicamycin and endoglycosidases on the structural glycoproteins

The monovalent ionophore monensin, which interferes with cellular transport pathways, and the antibiotic tunicamycin, which prevents glycosylation of newly synthesized proteins, were used to examine Hantaan virus particle formation and polypeptide synthesis. Viral replication in the presence of either drug resulted in reduced antigen production as well as reduced yields of both intracellular and extracellular infectious virus. Analysis of viral polypeptides synthesized in the presence of the drugs suggested differential effects of monensin and tunicamycin on Hantaan virus. Although reduced levels of the three major structural proteins were detected with increasing concentrations of monensin, the electrophoretic migrations of the polypeptides synthesized were unaltered. In contrast, after tunicamycin treatment, G1 was no longer detectable and G2 displayed both a quantitative reduction and an apparent molecular weight reduction of approximately 3000. Both G1 and G2 were sensitive to endoglycosidases H and F with resultant electrophoretic mobility shifts corresponding to molecular weights of approximately 7000 for G1 and 3000 for G2. Oligosaccharides appeared to be mostly, but not entirely, of the high-mannose type.

Antigenic and genetic properties of viruses linked to hemorrhagic fever with renal syndrome

Hemorrhagic fever with renal syndrome (HFRS) comprises a variety of clinically similar diseases of viral etiology that are endemic to and sporadically epidemic throughout the Eurasian continent and Japan. Although HFRS has not been reported in North America, viruses that are antigenically similar to HFRS agents were recently isolated from rodents in the United States. Examination and comparison of eight representative isolates from endemic disease areas and from regions with no known associated HFRS indicate that these viruses represent a new and unique group that constitutes a separate genus in the Bunyaviridae family of animal viruses.

Characterization of Hantaan virions, the prototype virus of hemorrhagic fever with renal syndrome

Hantaan virus, strain 76-118, was propagated to high titer in a clone of Vero cells, and infectious virions were successfully concentrated and purified. Infectivity and virus antigenic activity were closely associated with a virus particle that exhibited a sedimentation rate indistinguishable from a representative member of the Bunyaviridae. Purified virions sedimented to a density of 1.16-1.17 in sucrose and 1.20-1.21 in cesium chloride. Detergent disruption of virions resulted in a nucleocapsid structure (density, 1.18 in sucrose and 1.25 in cesium chloride) and soluble protein antigens. Three separate nucleocapsids were resolved by rate-zonal centrifugation and contained a single but common polypeptide of 50,000 daltons. Electrophoresis of radiolabeled RNA extracted from purified virions yielded a profile of three RNA species with apparent molecular weights of 2.7, 1.2, and 0.6 X 10(6). These data support earlier electron microscopy reports which suggested that Hantaan virus has characteristics similar to some members of the virus family Bunyaviridae.