Domain III of dengue virus E protein (DIII) participates in the recognition of cell receptors and in structural rearrangements required for membrane fusion and ultimately viral infection; furthermore, it contains epitopes for neutralizing antibodies and has been considered a potential vaccination agent. In this work, we addressed various structural aspects of DIII and their relevance for both the dengue virus infection mechanism and antibody recognition. We provided a dynamic description of DIII at physiological and endosomal pHs and in complex with the neutralizing human antibody DV32.6. We observed conformational exchange in the isolated DIII, in regions important for the packing of E protein dimers on the virus surface. This conformational diversity is likely to facilitate the partial detachment of DIII from the other E protein domains, which is required to achieve fusion to the host cellular membranes and to expose the epitopes of many anti-DIII antibodies. A comparison of DIII of two dengue virus serotypes revealed many common features but also some possibly unexpected differences. Antibody binding to DIII of dengue virus serotype 4 attenuated the conformational exchange in the epitope region but, surprisingly, generated exchange in other parts of DIII through allosteric effects.
IMPORTANCEMany studies have provided extensive structural information on the E protein and particularly on DIII, also in complex with antibodies. However, there is very scarce information regarding the molecular dynamics of DIII, and almost nothing is available on the dynamic effect of antibody binding, especially at the quantitative level. This work provides one of the very rare descriptions of the effect of antibody binding on antigen dynamics. D engue virus (DENV) is a member of the Flaviviridae family, which includes yellow fever, West Nile, Japanese tick-borne encephalitis, and other viruses. DENV is responsible for ϳ500,000 hospitalizations and Ͼ20,000 deaths per year (1). The incidence and geographic expansion of the virus are constantly increasing, and no cure or licensed vaccine is currently available for Dengue disease. There are four Dengue virus serotypes, DENV1 to -4, and secondary infection with a different serotype is associated with a severe form of the disease: dengue hemorrhagic fever (2). This is probably facilitated by a process called antibody-dependent enhancement (ADE), where cross-reactive, poorly neutralizing antibodies allow infection of Fc receptor-bearing cells, leading to increased viral loads and infectivity (3).Flaviviruses recognize their target cells via the interaction of glycoprotein E (E protein) with host receptors, which include the extracellular matrix components (4-6). After virus internalization by endocytosis, exposure to the lower endosomal pH leads to alterations of the E protein structure, exposing the fusion peptide and allowing it to interact with the endosome membrane and mediate viral fusion (1, 7-9).The virus surface is formed by 180 units of antiparallel E protein dimers (1...