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ABSTRACT: The replication of dengue virus (DENV) RNA requires at least two viral non-structural (NS) proteins, NS3 and NS5. To facilitate the study of the DENV replication complex, human monoclonal IgG that are specific for NS proteins have been generated and characterised. The anti-NS3 IgG, 3F8, binds a conserved epitope (aa526-531) in the NS3 helicase domain, and cross-reacts with NS3 from all four DENV serotypes and the related yellow fever virus. The anti-NS2B IgG, 3F10, binds aa49-66 of NS2B (CF18), which forms part of the 47 aa hydrophilic cofactor region required for NS3 protease activity. The specificity of the IgG for their respective non-structural proteins has been demonstrated by immunofluorescence of cells infected with DENV and Western blotting. 3F8 is able to co-immunoprecipitate NS3 and NS5 from BHK-21 cells infected with DENV2, and 3F10 is able to detect an interaction between recombinant NS2B(CF18)NS3 full-length protein and the NS5 RNA-dependent RNA polymerase (RdRp) domain in an ELISA-based binding assay. The assay is specific and highly reproducible, with a clear binding curve seen when RdRp is incubated with increasing amounts of full-length NS3, but not the NS3 protease domain. The NS3 helicase domain competes with NS3 full-length for NS5 RdRp binding, with a K(d.) of 2.5μM. Since NS3 and NS5 are required for DENV replication, this fascile assay could be used to screen for non-nucleoside, allosteric inhibitors that disrupt the interaction between the two proteins.
Journal of virological methods 01/2012; 179(1):97-103. · 2.13 Impact Factor
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ABSTRACT: Domain III of the dengue virus envelope protein (EDIII, aa295-395) has an immunoglobulin fold and is the proposed receptor-binding domain of the virus. Previous studies have shown that monoclonal antibodies against EDIII can be neutralizing and have therapeutic potential. Here, cloned Fab-phage libraries of human and mouse origin were screened for DENV specific antibodies. Firstly, bacterially expressed EDIII or whole virus particles were used as bait in biopanning against a large naïve human Fab-phage library (>10 billion independent clones). Multiple panning strategies were employed, and in excess of 1000 clones were screened, but all of the antibodies identified bound the envelope in regions outside EDIII suggesting EDIII antibodies are virtually absent from the naïve human repertoire. Next, a chimeric Fab-phage library was constructed from a panel of EDIII specific mouse hybridomas by pooling the VH and VL chain sequences from the hybridomas and cloning these into the pComb3X phagemid vector with human CH and CL encoding sequences. Biopanning against EDIII identified a unique antibody (C9) that cross-reacts with EDIII from DENV1-3 and, in the IgG format, binds and neutralizes DENV2 in cell-based assays. Sequence analysis and saturation mutagenesis of complementary determining regions (CDR) in the C9 light chain suggest an antigen recognition model in which the LCDR3 is a key determinant of EDIII specificity, while modifications in LCDR1 and LCDR2 affect DENV serotype cross-reactivity. Overall, this study supports the current prevailing opinion that neutralizing anti-EDIII monoclonal antibodies can be readily generated in murine systems, but in humans the anti-DENV immune response is directed away from domain III.
International Journal of Molecular Sciences 01/2012; 13(3):2618-35. · 2.60 Impact Factor
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ABSTRACT: The enzyme activities catalysed by flavivirus non-structural protein 3 (NS3) are essential for virus replication. They are distributed between the N-terminal protease domain in the first one-third and the C-terminal ATPase/helicase and nucleoside 5' triphosphatase domain which forms the remainder of the 618-aa long protein.
In this study, dengue full-length NS3 protein with residues 49 to 66 of NS2B covalently attached via a flexible linker, was used as bait in biopanning with a naïve human Fab phage-display library. Using a range of truncated constructs spanning the NS2B cofactor region and the full-length NS3, 10 unique Fab were identified and characterized. Of these, monoclonal Fab 3F8 was shown to bind α3″ (residues 526 through 531) within subdomain III of the helicase domain. The antibody inhibits the ATPase and helicase activites of NS3 in biochemical assays and reduces DENV replication in HEK293 cells that were previously transfected with Fab 3F8 compared with mock transfected cells.
Antibodies such as 3F8 are valuable tools for studying the molecular mechanisms of flaviviral replication and for the monospecific detection of replicating dengue virus in vivo.
PLoS Neglected Tropical Diseases 01/2010; 4(11):e881. · 4.69 Impact Factor
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ABSTRACT: The replication of dengue virus (DENV) RNA requires at least two viral non-structural (NS) proteins, NS3 and NS5. To facilitate the study of the DENV replication complex, human monoclonal IgG that are specific for NS proteins have been generated and characterised. The anti-NS3 IgG, 3F8, binds a conserved epitope (aa526-531) in the NS3 helicase domain, and cross-reacts with NS3 from all four DENV serotypes and the related yellow fever virus. The anti-NS2B IgG, 3F10, binds aa49-66 of NS2B (CF18), which forms part of the 47 aa hydrophilic cofactor region required for NS3 protease activity. The specificity of the IgG for their respective non-structural proteins has been demonstrated by immunofluorescence of cells infected with DENV and Western blotting. 3F8 is able to co-immunoprecipitate NS3 and NS5 from BHK-21 cells infected with DENV2, and 3F10 is able to detect an interaction between recombinant NS2BCF18NS3 full-length protein and the NS5 RNA-dependent RNA polymerase (RdRp) domain in an ELISA-based binding assay. The assay is specific and highly reproducible, with a clear binding curve seen when RdRp is incubated with increasing amounts of full-length NS3, but not the NS3 protease domain. The NS3 helicase domain competes with NS3 full-length for NS5 RdRp binding, with a Kd. of 2.5 μM. Since NS3 and NS5 are required for DENV replication, this fascile assay could be used to screen for non-nucleoside, allosteric inhibitors that disrupt the interaction between the two proteins.Highlights► The NS3–NS5 interaction is critical for dengue replication. ► Monoclonal antibodies to NS2B and NS3 have been generated to study dengue replication. ► The 3F8 IgG (anti-NS3) can pull-down NS3 and NS5 from dengue infected cells. ► The 3F10 IgG (anti-NS2B) detects an interaction between NS3 and NS5 in vitro. ► Protein interaction assays incorporating the IgG will be valuable for drug discovery research.
Journal of Virological Methods. 179(1):97-103.
