Proteomics Computational Analyses Suggest that the Antennavirus Glycoprotein Complex Includes a Class I Viral Fusion Protein (α-Penetrene) with an Internal Zinc-Binding Domain and a Stable Signal Peptide.
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SUBMITTER: Garry CE
PROVIDER: S-EPMC6722660 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BackgroundBorna disease virus (BDV) is the type member of the Bornaviridae, a family of viruses that induce often fatal neurological diseases in horses, sheep and other animals, and have been proposed to have roles in certain psychiatric diseases of humans. The BDV glycoprotein (G) is an extensively glycosylated protein that migrates with an apparent molecular mass of 84,000 to 94,000 kilodaltons (kDa). BDV G is post-translationally cleaved by the cellular subtilisin-like protease furin into two subunits, a 41 kDa amino terminal protein GP1 and a 43 kDa carboxyl terminal protein GP2.ResultsClass III viral fusion proteins (VFP) encoded by members of the Rhabdoviridae, Herpesviridae and Baculoviridae have an internal fusion domain comprised of beta sheets, other beta sheet domains, an extended alpha helical domain, a membrane proximal stem domain and a carboxyl terminal anchor. Proteomics computational analyses suggest that the structural/functional motifs that characterize class III VFP are located collinearly in BDV G. Structural models were established for BDV G based on the post-fusion structure of a prototypic class III VFP, vesicular stomatitis virus glycoprotein (VSV G).ConclusionThese results suggest that G encoded by members of the Bornavirdae are class III VFPs (gamma-penetrenes).
| S-EPMC2753318 | biostudies-literature
Project description:The envelope glycoprotein of the arenaviruses (GP-C) is unusual in that the mature complex retains the cleaved, 58-amino-acid signal peptide. Association of this stable signal peptide (SSP) has been shown to be essential for intracellular trafficking and proteolytic maturation of the GP-C complex. We identify here a specific and previously unrecognized role of SSP in pH-dependent membrane fusion. Amino acid substitutions that alter the positive charge at lysine K33 in SSP affect the ability of GP-C to mediate cell-cell fusion and the threshold pH at which membrane fusion is triggered. Based on the presumed location of K33 at or near the luminal domain of SSP, we postulate that SSP interacts with the membrane-proximal or transmembrane regions of the G2 fusion protein. This unique organization of the GP-C complex may suggest novel strategies for intervention in arenavirus infection.
| S-EPMC1563716 | biostudies-literature
Project description:The Bunyaviridae family of enveloped RNA viruses includes five genuses, orthobunyaviruses, hantaviruses, phleboviruses, nairoviruses and tospoviruses. It has not been determined which Bunyavirus protein mediates virion:cell membrane fusion. Class II viral fusion proteins (beta-penetrenes), encoded by members of the Alphaviridae and Flaviviridae, are comprised of three antiparallel beta sheet domains with an internal fusion peptide located at the end of domain II. Proteomics computational analyses indicate that the carboxyl terminal glycoprotein (Gc) encoded by Sandfly fever virus (SAN), a phlebovirus, has a significant amino acid sequence similarity with envelope protein 1 (E1), the class II fusion protein of Sindbis virus (SIN), an Alphavirus. Similar sequences and common structural/functional motifs, including domains with a high propensity to interface with bilayer membranes, are located collinearly in SAN Gc and SIN E1. Gc encoded by members of each Bunyavirus genus share several sequence and structural motifs. These results suggest that Gc of Bunyaviridae, and similar proteins of Tenuiviruses and a group of Caenorhabditis elegans retroviruses, are class II viral fusion proteins. Comparisons of divergent viral fusion proteins can reveal features essential for virion:cell fusion, and suggest drug and vaccine strategies.
| S-EPMC535339 | biostudies-literature
Project description:UnlabelledArenaviruses are responsible for severe and often fatal hemorrhagic disease. In the absence of effective antiviral therapies and vaccines, these viruses pose serious threats to public health and biodefense. Arenaviruses enter the host cell by fusion of the viral and endosomal membranes, a process mediated by the virus envelope glycoprotein GPC. Unlike other class I viral fusion proteins, GPC retains its stable signal peptide (SSP) as an essential third subunit in the mature complex. SSP spans the membrane twice and is myristoylated at its cytoplasmic N terminus. Mutations that abolish SSP myristoylation have been shown to reduce pH-induced cell-cell fusion activity of ectopically expressed GPC to ∼20% of wild-type levels. In order to examine the role of SSP myristoylation in the context of the intact virus, we used reverse genetics to generate Junín viruses (Candid #1 isolate) in which the critical glycine-2 residue in SSP was either replaced by alanine (G2A) or deleted (ΔG2). These mutant viruses produced smaller foci of infection in Vero cells and showed an ∼5-fold reduction in specific infectivity, commensurate with the defect in cell-cell fusion. However, virus assembly and GPC incorporation into budded virions were unaffected. Our findings suggest that the myristate moiety is cryptically disposed in the prefusion GPC complex and may function late in the fusion process to promote merging of the viral and cellular membranes.ImportanceHemorrhagic fever arenaviruses pose significant threats to public health and biodefense. Arenavirus entry into the host cell is promoted by the virus envelope glycoprotein GPC. Unlike other viral envelope glycoproteins, GPC contains a myristoylated stable signal peptide (SSP) as an essential third subunit. Myristoylation has been shown to be important for the membrane fusion activity of recombinantly expressed GPC. Here, we use reverse genetics to study the role of SSP myristoylation in the context of the intact virion. We find that nonmyristoylated GPC mutants of the Candid #1 strain of Junín virus display a commensurate deficiency in their infectivity, albeit without additional defects in virion assembly and budding. These results suggest that SSP myristoylation may function late in the fusion process to facilitate merging of the viral and cellular membranes. Antiviral agents that target this novel aspect of GPC membrane fusion may be useful in the treatment of arenavirus hemorrhagic fevers.
| S-EPMC5008094 | biostudies-literature
Project description:UnlabelledArenavirus species are responsible for severe life-threatening hemorrhagic fevers in western Africa and South America. Without effective antiviral therapies or vaccines, these viruses pose serious public health and biodefense concerns. Chemically distinct small-molecule inhibitors of arenavirus entry have recently been identified and shown to act on the arenavirus envelope glycoprotein (GPC) to prevent membrane fusion. In the tripartite GPC complex, pH-dependent membrane fusion is triggered through a poorly understood interaction between the stable signal peptide (SSP) and the transmembrane fusion subunit GP2, and our genetic studies have suggested that these small-molecule inhibitors act at this interface to antagonize fusion activation. Here, we have designed and synthesized photoaffinity derivatives of the 4-acyl-1,6-dialkylpiperazin-2-one class of fusion inhibitors and demonstrate specific labeling of both the SSP and GP2 subunits in a native-like Lassa virus (LASV) GPC trimer expressed in insect cells. Photoaddition is competed by the parental inhibitor and other chemically distinct compounds active against LASV, but not those specific to New World arenaviruses. These studies provide direct physical evidence that these inhibitors bind at the SSP-GP2 interface. We also find that GPC containing the uncleaved GP1-GP2 precursor is not susceptible to photo-cross-linking, suggesting that proteolytic maturation is accompanied by conformational changes at this site. Detailed mapping of residues modified by the photoaffinity adducts may provide insight to guide the further development of these promising lead compounds as potential therapeutic agents to treat Lassa hemorrhagic fever.ImportanceHemorrhagic fever arenaviruses cause lethal infections in humans and, in the absence of licensed vaccines or specific antiviral therapies, are recognized to pose significant threats to public health and biodefense. Lead small-molecule inhibitors that target the arenavirus envelope glycoprotein (GPC) have recently been identified and shown to block GPC-mediated fusion of the viral and cellular endosomal membranes, thereby preventing virus entry into the host cell. Genetic studies suggest that these inhibitors act through a unique pH-sensing intersubunit interface in GPC, but atomic-level structural information is unavailable. In this report, we utilize novel photoreactive fusion inhibitors and photoaffinity labeling to obtain direct physical evidence for inhibitor binding at this critical interface in Lassa virus GPC. Future identification of modified residues at the inhibitor-binding site will help elucidate the molecular basis for fusion activation and its inhibition and guide the development of effective therapies to treat arenaviral hemorrhagic fevers.
| S-EPMC4944282 | biostudies-literature
Project description:BackgroundMembers of the Baculoviridae encode two types of proteins that mediate virus:cell membrane fusion and penetration into the host cell. Alignments of primary amino acid sequences indicate that baculovirus fusion proteins of group I nucleopolyhedroviruses (NPV) form the GP64 superfamily. The structure of these viral penetrenes has not been determined. The GP64 superfamily includes the glycoprotein (GP) encoded by members of the Thogotovirus genus of the Orthomyxoviridae. The entry proteins of other baculoviruses, group II NPV and granuloviruses, are class I penetrenes.ResultsClass III penetrenes encoded by members of the Rhabdoviridae and Herpesviridae have an internal fusion domain comprised of beta sheets, other beta sheet domains, an extended alpha helical domain, a membrane proximal stem domain and a carboxyl terminal anchor. Similar sequences and structural/functional motifs that characterize class III penetrenes are located collinearly in GP64 of group I baculoviruses and related glycoproteins encoded by thogotoviruses. Structural models based on a prototypic class III penetrene, vesicular stomatitis virus glycoprotein (VSV G), were established for Thogoto virus (THOV) GP and Autographa california multiple NPV (AcMNPV) GP64 demonstrating feasible cysteine linkages. Glycosylation sites in THOV GP and AcMNPV GP64 appear in similar model locations to the two glycosylation sites of VSV G.ConclusionThese results suggest that proteins in the GP64 superfamily are class III penetrenes.
| S-EPMC2288602 | biostudies-literature
Project description:UNLABELLED:The rodent arenavirus glycoprotein complex encodes a stable signal peptide (SSP) that is an essential structural component of mature virions. The SSP, GP1, and GP2 subunits of the trimeric glycoprotein complex noncovalently interact to stud the surface of virions and initiate arenavirus infectivity. Nascent glycoprotein production undergoes two proteolytic cleavage events: first within the endoplasmic reticulum (ER) to cleave SSP from the remaining precursor GP1/2 (glycoprotein complex [GPC]) glycoprotein and second within the Golgi stacks by the cellular SKI-1/S1P for GP1/2 processing to yield GP1 and GP2 subunits. Cleaved SSP is not degraded but retained as an essential glycoprotein subunit. Here, we defined functions of the 58-amino-acid lymphocytic choriomeningitis virus (LCMV) SSP in regard to glycoprotein complex processing and maturation. Using molecular biology techniques, confocal microscopy, and flow cytometry, we detected SSP at the plasma membrane of transfected cells. Further, we identified a sorting signal (FLLL) near the carboxyl terminus of SSP that is required for glycoprotein maturation and trafficking. In the absence of SSP, the glycoprotein accumulated within the ER and was unable to undergo processing by SKI-1/S1P. Mutation of this highly conserved FLLL motif showed impaired glycoprotein processing and secretory pathway trafficking, as well as defective surface expression and pH-dependent membrane fusion. Immunoprecipitation of SSP confirmed an interaction between the signal peptide and the GP2 subunit; however, mutations within this FLLL motif disrupted the association of the GP1 subunit with the remaining glycoprotein complex. IMPORTANCE:Several members of the Arenaviridae family are neglected human pathogens capable of causing illness ranging from a nondescript flu-like syndrome to fulminant hemorrhagic fever. Infections by arenaviruses are mediated by attachment of the virus glycoprotein to receptors on host cells and virion internalization by fusion within an acidified endosome. SSP plays a critical role in the fusion of the virus with the host cell membrane. Within infected cells, the retained glycoprotein SSP plays a neglected yet essential role in glycoprotein biosynthesis. Without this 6-kDa polypeptide, the glycoprotein precursor is retained within the endoplasmic reticulum, and trafficking to the plasma membrane where SSP, GP1, and GP2 localize for glycoprotein assembly into infectious virions is inhibited. To investigate SSP contributions to glycoprotein maturation and function, we created an SSP-tagged glycoprotein to directly detect and manipulate this subunit. This resource will aid future studies to identify host factors that mediate glycoprotein maturation.
| S-EPMC4217180 | biostudies-literature
Project description:Ebolavirus (Ebov), an enveloped virus of the family Filoviridae, causes hemorrhagic fever in humans and nonhuman primates. The viral glycoprotein (GP) is solely responsible for virus-host membrane fusion, but how it does so remains elusive. Fusion occurs after virions reach an endosomal compartment where GP is proteolytically primed by cathepsins. Fusion by primed GP is governed by an internal fusion loop found in GP2, the fusion subunit. This fusion loop contains a stretch of hydrophobic residues, some of which have been shown to be critical for GP-mediated infection. Here we present liposome fusion data and NMR structures for a complete (54-residue) disulfide-bonded internal fusion loop (Ebov FL) in a membrane mimetic. The Ebov FL induced rapid fusion of liposomes of varying compositions at pH values at or below 5.5. Consistently, circular dichroism experiments indicated that the ?-helical content of the Ebov FL in the presence of either lipid-mimetic micelles or small liposomes increases in samples exposed to pH ?5.5. NMR structures in dodecylphosphocholine micelles at pH 7.0 and 5.5 revealed a conformational change from a relatively flat extended loop structure at pH 7.0 to a structure with an ?90° bend at pH 5.5. Induction of the bend at low pH reorients and compacts the hydrophobic patch at the tip of the FL. We propose that these changes facilitate disruption of lipids at the site of virus-host cell membrane contact and, hence, initiate Ebov fusion.
| S-EPMC3131375 | biostudies-literature
Project description:Jingmen viruses are newly described segmented flavi-like viruses that have a worldwide distribution in ticks and have been associated with febrile illnesses in humans. Computational analyses were used to predict that Jingmen flavi-like virus glycoproteins have structural features of class II viral fusion proteins, including an ectodomain consisting of beta-sheets and short alpha-helices, a fusion peptide with interfacial hydrophobicity and a three-domain architecture. Jingmen flavi-like virus glycoproteins have a sequence enriched in serine, threonine, and proline at the amino terminus, which is a feature of mucin-like domains. Several of the serines and threonines are predicted be modified by the addition of O-linked glycans. Some of the glycoproteins are predicted to have an additional mucin-like domain located prior to the transmembrane anchor, whereas others are predicted to have a stem consisting of two alpha-helices. The flavivirus envelope protein and Jingmen flavi-virus glycoproteins may have diverged from a common class II precursor glycoprotein with a mucin-like domain or domains acquired after divergence.
| S-EPMC7150890 | biostudies-literature
Project description:Alphaviruses infect cells via a low-pH-triggered membrane fusion reaction mediated by the class II virus fusion protein E1, an elongated molecule with three extramembrane domains (DI-III). E1 drives fusion by inserting its fusion peptide loop into the target membrane and refolding to a hairpin-like trimer in which DIII moves toward the target membrane and packs against the central trimer. Three-dimensional structures provide static pictures of prefusion and postfusion E1 but do not explain this transition. Using truncated forms of E1, we reconstituted a low-pH-dependent intermediate composed of trimers of DI/II. Unexpectedly, DI/II trimers were stable in the absence of DIII. Once formed at a low pH, DI/II trimers efficiently and specifically bound recombinant DIII through a pH-independent reaction. Even in the absence of DIII, DI/II trimers interacted to form hexagonal lattices and to cause membrane deformation and tubulation. These studies identify a prefusion intermediate in class II membrane fusion.
| S-EPMC2794427 | biostudies-literature