Structure of the St. Louis Encephalitis Virus Postfusion Envelope Trimer

Luca, Vincent C.; Nelson, Christopher A.; Fremont, Daved H.

doi:10.1128/jvi.01950-12

Cited by 27 publications

(32 citation statements)

References 79 publications

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“…However the unaffected fusion activity of the R902A in our functional assay suggests that it is not mandatory for fusion activity (S4B Fig). Indeed it was suggested before that there is no preferred distance between fusion loops of class II proteins required for fusion activity [49]. Finally, it was postulated that histidine residues function as pH sensors in class II membrane fusion proteins from flaviviruses [50–53].…”

Section: Resultsmentioning

confidence: 99%

Crystal Structure of Glycoprotein C from a Hantavirus in the Post-fusion Conformation

et al. 2016

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Hantaviruses are important emerging human pathogens and are the causative agents of serious diseases in humans with high mortality rates. Like other members in the Bunyaviridae family their M segment encodes two glycoproteins, GN and GC, which are responsible for the early events of infection. Hantaviruses deliver their tripartite genome into the cytoplasm by fusion of the viral and endosomal membranes in response to the reduced pH of the endosome. Unlike phleboviruses (e.g. Rift valley fever virus), that have an icosahedral glycoprotein envelope, hantaviruses display a pleomorphic virion morphology as GN and GC assemble into spikes with apparent four-fold symmetry organized in a grid-like pattern on the viral membrane. Here we present the crystal structure of glycoprotein C (GC) from Puumala virus (PUUV), a representative member of the Hantavirus genus. The crystal structure shows GC as the membrane fusion effector of PUUV and it presents a class II membrane fusion protein fold. Furthermore, GC was crystallized in its post-fusion trimeric conformation that until now had been observed only in Flavi- and Togaviridae family members. The PUUV GC structure together with our functional data provides intriguing evolutionary and mechanistic insights into class II membrane fusion proteins and reveals new targets for membrane fusion inhibitors against these important pathogens.

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Section: Resultsmentioning

confidence: 99%

Crystal Structure of Glycoprotein C from a Hantavirus in the Post-fusion Conformation

et al. 2016

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“…These E structures differ not only by oligomeric status, but also display changes in relative conformations and angles among the three E protein domains. Similar E protein structures at various stages of virus development and infection have also been solved for related flaviviruses, such as tick-borne encephalitis virus, yellow fever virus, West Nile virus, Japanese encephalitis virus, and St. Louis encephalitis virus (8,(18)(19)(20)(21)(22)(23)(24).Although the many structures of DENV E protein provide static images of the protein at various stages of infectivity, the key functional residues that mediate the dynamic fusion process Significance Dengue virus (DENV) infects nearly 400 million people annually, and approximately 40% of the world's population lives at risk for infection. Without a therapeutic or vaccine available, DENV remains a major public health burden.…”

mentioning

confidence: 84%

mentioning

confidence: 86%

Atomic-level functional model of dengue virus Envelope protein infectivity

Christian

Kahle

Mattia

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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A number of structures have been solved for the Envelope (E) protein from dengue virus and closely related flaviviruses, providing detailed pictures of the conformational states of the protein at different stages of infectivity. However, the key functional residues responsible for mediating the dynamic changes between these structures remain largely unknown. Using a comprehensive library of functional point mutations covering all 390 residues of the dengue virus E protein ectodomain, we identified residues that are critical for virus infectivity, but that do not affect E protein expression, folding, virion assembly, or budding. The locations and atomic interactions of these critical residues within different structures representing distinct fusogenic conformations help to explain how E protein (i) regulates fusion-loop exposure by shielding, tethering, and triggering its release; (ii) enables hinge movements between E domain interfaces during triggered structural transformations; and (iii) drives membrane fusion through latestage zipper contacts with stem. These results provide structural targets for drug and vaccine development and integrate the findings from structural studies and isolated mutagenesis efforts into a cohesive model that explains how specific residues in this class II viral fusion protein enable virus infectivity. D engue virus (DENV) infection of target cells proceeds through a membrane-fusion step, catalyzed by a viral fusion protein. The DENV genome, like that of other flaviviruses, encodes a single polyprotein that is processed into three structural proteins-capsid (C), precursor membrane (prM), and envelope (E)-and seven nonstructural proteins that are required for viral replication. The capsid protein and the viral RNA genome form a nucleocapsid that buds at the endoplasmic reticulum (ER) in association with 180 copies each of prM and E, as well as host-derived lipids, to form the immature virion (1). This noninfectious virion passes through the cell's secretory pathway, maturing in the Golgi where most of the prM proteins are cleaved into pr and M proteins by the host protease furin (2). The mature virions bud from the cell via exocytosis and are then available to infect new cells.DENV infects a cell by binding of E protein to one or more receptors on the cell surface, followed by clathrin-mediated endocytosis and transport to endosomes (3). The three distinct ectodomains (DI, DII, and DIII) of E protein lie over a helical stem region tethered to the virus membrane by a transmembrane anchor. In the acidic endosome, protonation of E protein histidine residues is thought to mediate conformational changes that trigger the dissociation of the E dimer into monomers and subsequent rearrangements among DI, DII, and DIII (4, 5). These conformational changes enable formation of the fusogenic E trimer and insertion of E protein into the endosomal membrane by means of a fusion loop (6, 7). Fusion between the viral and endosomal membranes is then driven by a portion of the E stem region lifting off t...

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“…Molecular dynamics simulations at low pH have suggested that trimeric, stemless sE might adopt this open conformation (24). Indeed, a recent stemless flavivirus crystal structure reveals splayed fusion loops at an intermediate distance, 17 Å, from the 3-fold axis, 5 Å farther than in the closed conformation (25). It has also been proposed that during the final stages of fusion, the H1 segment of the stem would squeeze between adjacent domains II, maintaining the splayed conformation (7).…”

Section: Dengue Virus Envelope Trimer With Proximal Stemmentioning

confidence: 99%

Structure of a Dengue Virus Envelope Protein Late-Stage Fusion Intermediate

Klein

Choi

Harrison

2013

J Virol

127

147

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The final stages of dengue virus fusion are thought to occur when the membrane-proximal stem drives the transmembrane anchor of the viral envelope protein (E) toward the fusion loop, buried in the target cell membrane. Crystal structures of E have lacked this essential stem region. We expressed and crystallized soluble mutant forms of the dengue virus envelope protein (sE) that include portions of the juxtamembrane stem. Their structures represent late-stage fusion intermediates. The proximal part of the stem has both intra-and intermolecular interactions, so the chain "zips up" along the trimer seam. The penultimate interaction we detected involves the conserved residue F402, which has hydrophobic contacts with a conserved surface on domain II. These interactions do not require any larger-scale changes in trimer packing. The techniques for expression and crystallization of sE containing stem reported here may allow further characterization of the final stages of flavivirus fusion. The membrane-spanning envelope glycoprotein protein (E) of flaviviruses is both the principal determinant of icosahedral virion assembly and the fusion catalyst for merging viral and target cell membranes ( Fig. 1) (1, 2). The E protein folds into three domains, a membrane-proximal stem, and a transmembrane anchor (Fig. 1A). Various crystal structures have shown the arrangement of the three folded domains in both a dimeric prefusion conformation ( Fig. 1C) (3, 6) and a low-pHinduced postfusion trimer ( Fig. 1F) (4, 7). The hydrophobic fusion loops, buried at the dimer interface in the prefusion structure (3, 5, 6), cluster into a large hydrophobic surface at one end of the postfusion trimer (4,7,8). In this orientation, the fusion loops attach the virus to the target cell membrane. The membrane-proximal stem has two predicted amphipathic helices that lie half-buried in the outer leaflet of the viral membrane ( Fig. 1C) (9,10). For fusion to take place, this stem must span the length of domain II (Fig. 1F). A likely model is that it "zips up" along the gaps between the clustered domains, bringing together the transmembrane anchor and the fusion loops, inducing deformation of their associated membranes and leading to membrane merger.Several studies show the importance of the amino-terminal part of the stem and suggest that it forms contacts with domain II as the fusion-inducing transition proceeds (11-13). Efforts to visualize it directly in this conformation have failed, however, because including the stem residues in recombinant E generally leads to instability or aggregation of any secreted product. We describe here a method for producing sE that includes portions of the juxtamembrane stem and report its crystallization and structure determination. The structure shows that the N-terminal part of the stem zips up along the seam between adjacent domains II in the trimer. The rest of the stem in our constructs is disordered. The arrangement of the trimer core is the same as in previous, stemless structures. The results are consistent wi...

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Structure of the St. Louis Encephalitis Virus Postfusion Envelope Trimer

Cited by 27 publications

References 79 publications

Crystal Structure of Glycoprotein C from a Hantavirus in the Post-fusion Conformation

Crystal Structure of Glycoprotein C from a Hantavirus in the Post-fusion Conformation

Atomic-level functional model of dengue virus Envelope protein infectivity

Structure of a Dengue Virus Envelope Protein Late-Stage Fusion Intermediate

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