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Structure of the St. Louis Encephalitis Virus envelope protein in the fusogenic trimer conformation.
Structural highlights
FunctionPOLG_STEVM Plays a role in virus budding by binding to the cell membrane and gathering the viral RNA into a nucleocapsid that forms the core of a mature virus particle. During virus entry, may induce genome penetration into the host cytoplasm after hemifusion induced by the surface proteins. Can migrate to the cell nucleus where it modulates host functions. Overcomes the anti-viral effects of host EXOC1 by sequestering and degrading the latter through the proteasome degradation pathway.[UniProtKB:P17763] Inhibits RNA silencing by interfering with host Dicer.[UniProtKB:P03314] Prevents premature fusion activity of envelope proteins in trans-Golgi by binding to envelope protein E at pH6.0. After virion release in extracellular space, gets dissociated from E dimers.[UniProtKB:P17763] Acts as a chaperone for envelope protein E during intracellular virion assembly by masking and inactivating envelope protein E fusion peptide. prM is the only viral peptide matured by host furin in the trans-Golgi network probably to avoid catastrophic activation of the viral fusion activity in acidic Golgi compartment prior to virion release. prM-E cleavage is inefficient, and many virions are only partially matured. These uncleaved prM would play a role in immune evasion.[UniProtKB:P17763] May play a role in virus budding. Exerts cytotoxic effects by activating a mitochondrial apoptotic pathway through M ectodomain. May display a viroporin activity.[UniProtKB:P17763] Binds to host cell surface receptor and mediates fusion between viral and cellular membranes. Envelope protein is synthesized in the endoplasmic reticulum in the form of heterodimer with protein prM. They play a role in virion budding in the ER, and the newly formed immature particle is covered with 60 spikes composed of heterodimer between precursor prM and envelope protein E. The virion is transported to the Golgi apparatus where the low pH causes dissociation of PrM-E heterodimers and formation of E homodimers. prM-E cleavage is inefficient, and many virions are only partially matured. These uncleaved prM would play a role in immune evasion.[UniProtKB:P17763] Involved in immune evasion, pathogenesis and viral replication. Once cleaved off the polyprotein, is targeted to three destinations: the viral replication cycle, the plasma membrane and the extracellular compartment. Essential for viral replication. Required for formation of the replication complex and recruitment of other non-structural proteins to the ER-derived membrane structures. Excreted as a hexameric lipoparticle that plays a role against host immune response. Antagonizing the complement function. Binds to the host macrophages and dendritic cells. Inhibits signal transduction originating from Toll-like receptor 3 (TLR3).[UniProtKB:Q9Q6P4] Component of the viral RNA replication complex that functions in virion assembly and antagonizes the host alpha/beta interferon antiviral response.[UniProtKB:P14335] Required cofactor for the serine protease function of NS3. May have membrane-destabilizing activity and form viroporins (By similarity).[UniProtKB:P17763][PROSITE-ProRule:PRU00859] Displays three enzymatic activities: serine protease, NTPase and RNA helicase. NS3 serine protease, in association with NS2B, performs its autocleavage and cleaves the polyprotein at dibasic sites in the cytoplasm: C-prM, NS2A-NS2B, NS2B-NS3, NS3-NS4A, NS4A-2K and NS4B-NS5. NS3 RNA helicase binds RNA and unwinds dsRNA in the 3' to 5' direction.[PROSITE-ProRule:PRU00860] Regulates the ATPase activity of the NS3 helicase activity. NS4A allows NS3 helicase to conserve energy during unwinding.[UniProtKB:Q9Q6P4] Functions as a signal peptide for NS4B and is required for the interferon antagonism activity of the latter.[UniProtKB:P17763] Induces the formation of ER-derived membrane vesicles where the viral replication takes place. Inhibits interferon (IFN)-induced host STAT1 phosphorylation and nuclear translocation, thereby preventing the establishment of cellular antiviral state by blocking the IFN-alpha/beta pathway. Inhibits STAT2 translocation in the nucleus after IFN-alpha treatment.[UniProtKB:Q9Q6P4] Replicates the viral (+) and (-) RNA genome, and performs the capping of genomes in the cytoplasm. NS5 methylates viral RNA cap at guanine N-7 and ribose 2'-O positions. Besides its role in RNA genome replication, also prevents the establishment of cellular antiviral state by blocking the interferon-alpha/beta (IFN-alpha/beta) signaling pathway. Inhibits host TYK2 and STAT2 phosphorylation, thereby preventing activation of JAK-STAT signaling pathway.[UniProtKB:Q9Q6P4] Publication Abstract from PubMedSt. Louis encephalitis virus (SLEV) is a mosquito borne flavivirus responsible for several human encephalitis outbreaks over the last 80 years. Mature flavivirus virions are coated with dimeric envelope (E) proteins that mediate attachment and fusion with host cells. E is a class II fusion protein, the hallmark of which is a distinct dimer-to-trimer rearrangement that occurs upon endosomal acidification and insertion of hydrophobic fusion peptides into the endosomal membrane. Herein, we report the crystal structure of SLEV E in the posfusion trimer conformation. The structure revealed specific features that differentiate SLEV E from trimers of related flavi- and alphaviruses. SLEV E fusion loops have distinct intermediate spacing such that they are positioned further apart than previously observed in flaviviruses but closer together than Semliki Forest Virus, an alphavirus. Domains II (DII) and III (DIII) of SLEV E also adopt different angles relative to domain I (DI) which suggests the DI-DII joint may accommodate spheroidal motions. However, trimer interfaces are well conserved amongst flaviviruses, so it is likely the differences observed represent structural features specific to SLEV function. Analysis of surface potentials revealed a basic platform underneath flavivirus fusion loops that may interact with the anionic lipid head groups found in membranes. Taken together, these results highlight variation in E structure and assembly that may direct virus-specific interactions with host determinants to influence pathogenesis. Structure of the St. Louis encephalitis virus postfusion envelope trimer.,Luca VC, Nelson CA, Fremont DH J Virol. 2012 Oct 31. PMID:23115296[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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