Nucleotide sequence of the envelope glycoprotein gene of a dengue-2 virus isolated during an epidemic of benign dengue fever in Tonga in 1974

Origin and distribution of divergent dengue virus: novel database construction and phylogenetic analyses

Dengue virus (DENV), a mosquito-borne agent that exists as four serotypes (DENV-1–4), induces dengue illness. DENV has a positive-sense, ssRNA genome of approximately 11 kb that encodes a capsid protein, a premembrane protein and an envelope glycoprotein, in addition to seven nonstructural proteins. These individual genes show sequence variations that can be analyzed phylogenetically to yield several genotypes within each serotype. Here, the sequences of individual DENV genes were collected and used to construct a novel DENV database. This database was then used to characterize the evolution of individual genotypes in several countries. Interestingly, the database provided evidence for recombination between two or three different genotypes to yield new genotypes. This novel database will be available on the internet and is expected to be highly useful for dengue genetic studies, including phylogenetic analyses.

Dengue virus infectivity depends on envelope protein binding to target cell heparan sulfate

Dengue virus is a human pathogen that has reemerged as an increasingly important public health threat. We found that the cellular receptor utilized by dengue envelope protein to bind to target cells is a highly sulfated type of heparan sulfate. Heparin, highly sulfated heparan sulfate, and the polysulfonate pharmaceutical Suramin effectively prevented dengue virus infection of target cells, indicating that the envelope protein-target cell receptor interaction is a critical determinant of infectivity. The dengue envelope protein sequence includes two putative glycosaminoglycan-binding motifs at the carboxy terminus; the first could be structurally modeled and formed an unusual extended binding surface of basic amino acids. Similar motifs were also identified in the envelope proteins of other flaviviridae. Developing pharmaceuticals that inhibit target cell binding may be an effective strategy for treating flavivirus infections.

Demonstration of binding of dengue virus envelope protein to target cells

The nature of the initial interaction of dengue virus with target cells and the extent to which this interaction defines tropism are unknown. Infection of some cells may involve antidengue antibody-mediated immune adherence to cells bearing immunoglobulin Fc receptors; however, this mechanism does not explain primary infection or the infection of cells without Fc receptors. We hypothesized that dengue virus envelope protein mediates initial binding to target cells. To test this hypothesis, a recombinant chimeric form of dengue type 2 virus envelope protein was used as a probe to investigate binding to the surfaces of potential target cells. Envelope protein was expressed amino terminal to the heavy-chain constant region of human immunoglobulin G containing the Fc receptor binding motif; the binding mediated by envelope determinants was distinguishable from the binding mediated by immunoglobulin Fc determinants. We found that the recombinant chimera bound to Vero, CHO, endothelial, and glial cells through envelope protein determinants and to monocytes and U937 cells by Fc-Fc receptor interactions. The highest level of binding was to Vero cells; binding was dose and time dependent and saturable. Examination of partial-length recombinant envelope proteins indicated that the binding motif was expressed between amino acids 281 and 423. Recombinant envelope protein inhibited infection of Vero cells by dengue virus, indicating the functional significance of the interaction of envelope protein and target cells in infectivity. These results suggest that envelope protein binding to a non-Fc receptor could explain the cell and tissue tropism of primary dengue virus infection.

Molecular comparison of dengue type 1 Mochizuki strain virus and other selected viruses concerning nucleotide and amino acid sequences of genomic RNA: a consideration of viral epidemiology and variation

Dengue-1 (D1) Mochizuki strain was examined for its nucleotide and amino acid sequences of genomic RNA and the data obtained were compared with those of other selected virus strains reported previously. Genomic regions corresponding to C, preM and M proteins were the major subjects of study. Parts of E protein were additionally examined. Among the D1 viruses investigated, the Mochizuki virus which was isolated in 1943 in Japan was shown to be close to Philippine 836-1 strain isolated in 1984 and Nauru Island strain isolated in 1974 at the respective places, in contrast with Thai AHF 82-80 strain isolated in 1980 and Caribbean CV1636/77 strain isolated in 1977. At the same time, a difference was noted between the Mochizuki and Philippine/Nauru strains at the cleavage site of preM/M junction: Mochizuki possessed RRGKR/S sequence whereas the Philippine/Nauru had RRDKR/S. The glycosylation site in preM and hydrophobic regions at the carboxyl termini of M and E were well conserved. Significances of the data are discussed in connection with viral epidemiology and variation.

A simple and rapid method of preparing large fragments of dengue virus cDNA from replicative-form RNA using reverse transcriptase and PCR

A method is described for cloning large fragments (1.5 kb to 2 kb) of dengue virus cDNA from replicative-form viral RNA. Aedes albopictus cells (C6/36 clone) infected with dengue virus contain double-stranded, replicative-form RNA molecules which were used as a template for an initial reverse transcription using a primer containing sequence homologous to regions of the genome at or near the 3' end of the gene being studied. The product was then used as a template for polymerase chain reaction (PCR) amplification using the same 3' primer and a second which hybridized to a region at the 5' end of the sequence to be cloned. Both primers were engineered to contain specific restriction enzyme cutting sites which enabled the PCR product to be cut and cloned directly into plasmids for sequencing and expression studies. We have used this method to construct clones of the envelope glycoprotein gene (E) and the non-structural genes 1 and 2a (NS1/2a) and 3 (NS3) of dengue type 2, Tonga 1974 strain, and E and NS1/2a from dengue type 3, H-87 strain, either as discrete genes or as constructs with long and short leader sequences, with or without anchor sequences. The method could be applied to the cloning of any gene from any flavivirus, directly from infected cell extracts, without the necessity for tedious virus purification steps.