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Dengue disease is caused by four different flavivirus1 serotypes, which infect 390 million people yearly with 25% symptomatic cases2 and for which no licensed vaccine is available. Recent phase III vaccine trials showed partial protection, and in particular no protection for dengue virus serotype 2 (refs 3, 4). Structural studies so far have characterized only epitopes recognized by serotype-specific human antibodies5,6. We recently isolated human antibodies potently neutralizing all four dengue virus serotypes7. Here we describe the X-ray structures of four of these broadly neutralizing antibodies in complex with the envelope glycoprotein E from dengue virus serotype 2, revealing that the recognition determinants are at a serotype-invariant site at the E-dimer interface, including the exposed main chain of the E fusion loop8 and the two conserved glycan chains. This 'E-dimer-dependent epitope' is also the binding site for the viral glycoprotein prM during virus maturation in the secretory pathway of the infected cell9, explaining its conservation across serotypes and highlighting an Achilles' heel of the virus with respect to antibody neutralization. These findings will be instrumental for devising novel immunogens to protect simultaneously against all four serotypes of dengue virus.
Exposed at the surface of infectious mature dengue virus (DENV) particles, protein E is the sole target of neutralizing antibodies. It displaysan icosahedralarrangementinwhich90 E dimers completelycoat the viral surface10,11 and which is sensitive to the environmental pH. Upon entry of DENV into cells via receptor-mediated endocytosis, the acidic endosomal environment triggers an irreversible fusogenic conformational change in protein E that leads to fusion of viral and endosomal membranes1. A large fragment of E (termed sE for 'soluble E') lacking the C-terminal transmembrane anchor and a segment immediately preceding it (termed 'stem'), crystallizes as a dimer mimicking the organization of protein E on virions. The structure of the sE dimer hasbeen determinedby X-raycrystallography8,12. Protein E isrelatively conserved, displaying about 65% amino-acid sequence identity when comparing the most distant DENV serotypes. In particular, there are two conserved N-linked glycosylation sites at positions N67 and N153. To examine its interaction with the antibodies, we selected four highly potent broadlyneutralizingantibodies(bnAbs) identifiedinthe accompanying work: 747(4) A11 and 747 B7 ('E-dimer-dependent epitope 2' (EDE2) group, requiring glycosylation at position N153 for efficient binding) and 752-2 C8 and 753(3) C10 (EDE1 group,...