There are four closely-related dengue virus (DENV) serotypes. Infection with one serotype generates antibodies that may cross-react and enhance infection with other serotypes in a secondary infection. We demonstrated that DENV serotype 2 (DENV2)–specific human monoclonal antibody (HMAb) 2D22 is therapeutic in a mouse model of antibody-enhanced severe dengue disease. We determined the cryo–electron microscopy (cryo-EM) structures of HMAb 2D22 complexed with two different DENV2 strains. HMAb 2D22 binds across viral envelope (E) proteins in the dimeric structure, which probably blocks the E protein reorganization required for virus fusion. HMAb 2D22 “locks” two-thirds of or all dimers on the virus surface, depending on the strain, but neutralizes these DENV2 strains with equal potency. The epitope defined by HMAb 2D22 is a potential target for vaccines and therapeutics.

Dengue virus is a major human pathogen that has four serotypes (DENV1 to -4). Here we report the cryoelectron microscopy (cryo-EM) structures of immature and mature DENV1 at 6-and 4.5-Å resolution, respectively. The subnanometer-resolution maps allow accurate placement of all of the surface proteins. Although the immature and mature viruses showed vastly different surface protein organizations, the envelope protein transmembrane (E-TM) regions remain in similar positions. The pivotal role of the E-TM regions leads to the identification of the start and end positions of all surface proteins during maturation. Dengue virus (DENV), the cause of dengue fever, infects 100 million people worldwide every year. It is a member of the Flaviviridae family (1), with four serotypes: DENV1, -2, -3, and -4. Infection with DENV usually causes a self-limiting fever accompanied by rashes and joint pain in patients but might lead to dengue hemorrhagic fever and dengue shock syndrome, which may be fatal.DENV consists of an ϳ500-Å-diameter protein shell embedded in a host-derived lipid membrane and encapsidates an 11-kb single-stranded positive-sense RNA genome. The dengue genome encodes three structural proteins, the core (or capsid), the premembrane (prM), and the envelope (E) protein, that form the virus particle, as well as seven nonstructural proteins (1) that are involved in replication of the virus genome. The newly synthesized immature DENV has a spiky appearance (2) (Fig. 1A) and is typically noninfectious unless it is complexed with certain antibodies (3). Virus maturation occurs during transportation of the virus particle through the trans-Golgi component network (TGN). The acidic environment of these compartments induces structural rearrangement of the virus surface proteins. During this initial maturation process, the furin protease cleaves prM molecules on the virus into pr and M. After leaving the cell, the cleaved pr dissociates from the virus surface, resulting in smooth, fully mature infectious virus particles (4) (Fig. 1B).The E protein is the major structural component of the viral surface. The ectodomain of E protein (5) contains three distinct domains, DI, DII, and DIII (also shown in Fig. 1C), which are connected by flexible links that allow rearrangement of domains during virus assembly, maturation, and infection (5-7). DIII is involved in attachment to host cell receptors, whereas DII is responsible for fusion to the host endosomal membrane during infection (8). The ectodomain is connected to the stem made from amphipathic helices ␣1 and ␣2. The stem, in turn, is anchored to the virus lipid membrane by two transmembrane (TM) ␣-helices, TM1 and TM2.The crystal structure of an E-prM complex (6) shows that pr has a ␤-barrel fold and caps the fusion loop of the E protein, consistent with its function in preventing the newly synthesized virus from fusing back into the cell during maturation. The furin cleavage site lies between the pr molecule and the ectodomain of M protein, which exists as a linear polypeptide ...

Dengue virus (DENV) infects ~400 million people annually. There is no licensed vaccine or therapeutic drug. Only a small fraction of the total DENV-specific antibodies in a naturally occurring dengue infection consists of highly neutralizing antibodies. Here we show that the DENV-specific human monoclonal antibody 5J7 is exceptionally potent, neutralizing 50% of virus at nanogram-range antibody concentration. The 9 Å resolution cryo-electron microscopy structure of the Fab 5J7–DENV complex shows that a single Fab molecule binds across three envelope proteins and engages three functionally important domains, each from a different envelope protein. These domains are critical for receptor binding and fusion to the endosomal membrane. The ability to bind to multiple domains allows the antibody to fully coat the virus surface with only 60 copies of Fab, that is, half the amount compared with other potent antibodies. Our study reveals a highly efficient and unusual mechanism of molecular recognition by an antibody.

Dengue virus (DENV), which consists of four serotypes (DENV1-4), infects over 400 million people annually. Previous studies have indicated most human monoclonal antibodies (HMAbs) from dengue patients are cross-reactive and poorly neutralizing. Rare neutralizing HMAbs are usually serotype-specific and bind to quaternary structure-dependent epitopes. We determined the structure of DENV1 complexed with Fab fragments of a highly potent HMAb 1F4 to 6 Å resolution by cryo-EM. Although HMAb 1F4 appeared to bind to virus and not E proteins in ELISAs in the previous study, our structure showed that the epitope is located within an envelope (E) protein monomer, and not across neighboring E proteins. The Fab molecules bind to domain I (DI), and DI-DII hinge of the E protein. We also showed that HMAb 1F4 can neutralize DENV at different stages of viral entry in a cell type and receptor dependent manner. The structure reveals the mechanism by which this potent and specific antibody blocks viral infection.Subject Categories Microbiology, Virology & Host Pathogen Interaction; Immunology