The active essential CFNS3d protein complex: A new perspective for the structural and kinetic characterization of the NS2B–NS3pro complex of dengue virus

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The NS2B–NS3 protease complex is essential for the replication of dengue virus, which is the etiologic agent of dengue and hemorrhagic fevers, diseases that are a burden for the tropical and subtropical areas of the world. The active form of the NS3 protease linked to the 40 residues of the NS2B cofactor shows highly flexible and disordered region(s) that are responsible for its high propensity to aggregate at the concentrations necessary for NMR spectroscopy studies or for crystallization. Limited proteolysis of this active form of the protease enabled us to obtain a folded and new essential form of the NS2B–NS3 protease complex. We found that the region from residues D50 to E80 of NS2B interacts directly and strongly with the NS3 protease domain. The proteolytic activity of the noncovalently binding complex was determined by a rapid and continuous fluorescence resonance energy transfer activity assay using a depsipeptide substrate. The new protein–cofactor complex obtained, encompassing the NS2B fragment (D50–E80) and the NS3 protease, shows proteolytic activity. The 1H-15N-heteronuclear single quantum coherence spectrum of the isotopically enriched protein complex shows good cross-peak dispersion; this is indicative of a stable folded state. Our results significantly complement the X-ray structure of the NS2B–NS3pro complex published recently. Moreover, these results open the way to performing direct structural and interaction studies in solution on a new active NS2B–NS3pro complex with libraries of substrates and inhibitors in order to identify new drugs that prevent viral polyprotein processing.

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