Cell membrane Complex Enzyme Eukaryotic cell or cell component Microbe-host cell complex Microorganism or its component Other Other -- ion Pathway or action Protein Protein or gene Protein or gene complex Protein or protein complex Bacterial membrane or virus envelope Cell membrane Cytoplasm Eukaryotic cell or cell component Extracellular Golgi Golgi membrane Intercellular Intracellular Mitochondria Nucleocapsid/Cytoplasm Organelle Organelle -- Cell membrane Organelle -- Endoplasmic reticulum Organelle -- ER Organelle -- Golgi Organelle -- Golgi membrane Organelle -- Nucleus Organelle -- Phagolysosome Organelle -- Phagosome Organelle -- Ribosome Other Phagolysosome Phagosome Chaperone Defense, immunity protein Enzyme Enzyme activator Enzyme inhibitor Genomic S segment Infection Ligand binding or carrier Motor Nucleic acid binding Other Signal transducer Toxicity Transcription factor binding Transcription regulation Transporter Unknown IC Inferred by Curator IDA Inferred from Direct Assay IEA Inferred from Electronic Annotation IEP Inferred from Expression Pattern IGI Inferred from Genetic Interaction IMP Inferred from Mutant Phenotype IPI Inferred from Physical Interaction ISS Inferred from Sequence or Structural Similarity NAS Non-traceable Author Statement ND No biological Data available RCA inferred from Reviewed Computational Analysis TAS Traceable Author Statement NR Not Recorded Bavari S, Bosio CM, Wiegand E, Ruthel G, Will AB, Geisbert TW, Hevey M, Schmaljohn C, Schmaljohn A, Aman MJ The Journal of experimental medicine Lipid raft microdomains: a gateway for compartmentalized trafficking of Ebola and Marburg viruses 20024 11877482 PubMed Chan SY, Ma MC, Goldsmith MA The Journal of general virology Differential induction of cellular detachment by envelope glycoproteins of Marburg and Ebola (Zaire) viruses 2000 10950971 PubMed Volchkov VE Marburg and Ebola viruses Processing of infectious Ebola virus glycoprotein 1999 Jeffers SA, Sanders DA, Sanchez A Journal of virology Covalent modifications of the ebola virus glycoprotein 2002 12438572 PubMed Modrof J, Becker S, Muhlberger E Journal of virology Ebola virus transcription activator VP30 is a zinc-binding protein 2003 12584359 PubMed Han Z, Boshra H, Sunyer JO, Zwiers SH, Paragas J, Harty RN Journal of virology Biochemical and functional characterization of the Ebola virus VP24 protein: implications for a role in virus assembly and budding 2003 12525613 PubMed Huang Y, Xu L, Sun Y, Nabel GJ Molecular cell The assembly of Ebola virus nucleocapsid requires virion-associated proteins 35 and 24 and posttranslational modification of nucleoprotein 2002 12191476 PubMed Feldmann H and Kiley MP Marburg and Ebola viruses Classification, structure, and replication of filoviruses 1999 Peters CJ, Sanchez A, Rollin PE, Ksiazek TG, and Murphy FA Field's Virology Third Edition Volume 1 Filoviridae: Marburg and Ebola Viruses 1999 Bray M, Paragas J Antiviral research Experimental therapy of filovirus infections 2002 11888653 PubMed Feldmann H, Volchkov VE, Volchkova VA, Stroher U, Klenk HD The Journal of general virology Biosynthesis and role of filoviral glycoproteins 2001 11714958 PubMed GP Function: Ligand binding or carrier. Cell entry is presumably mediated by GP (Feldmann and Kiley, 1999). Each molecule in the trimeric GP is composed of an external segment, GP1, which is linked by a disulfide bond to a transmembrane unit, GP2 (Bray and Paragas, 2002). Several groups have demonstrated independently that the transmembrane glycoprotein of filoviruses mediates receptor binding and subsequent fusion with susceptible cells (Feldmann et al., 2001).(Feldmann et al., 2001)(Bray et al., 2002)(Feldmann2) Cell membrane receptor Function: Ligand binding or carrier. There is evidence that Marburg virus uses the asialoglycoprotein receptor to infect hepatocytes. For Ebola virus, it was suggested that integrins, especially the Beta1 group, might interact with the glycoprotein and perhaps be involved in entry into the cells. More recent studies indicate that the folate receptor-alpha serves as a cofactor for cellular entry by Marburg and Ebola viruses (Feldmann et al., 2001).(Feldmann et al., 2001) Attached virus Function: . Replication begins with the attachment of the virion to a cell-surface receptor, which may be the alpha-folate receptor. After binding, the virus enters the cell through receptor-mediated endocytosis (Bray and Paragas, 2002).(Bray et al., 2002) Fused virus Function: . Fusion of the viral envelope with the cellular endosomal membrane releases the RNP into the cytoplasm (Bray and Paragas, 2002). Fusion activity has never been demonstrated experimentally. Early post-infection filovirus particles are associated with coated pits along the plasma membrane, indicating endocytosis as a possible mechanism for entry. This observation, together with mutational analysis of the putative fusion domain, offers compelling support for a role for the conserved hydrophobic region in the Ebola virus transmembrane glycoprotein GP as a fusion peptide (Feldmann et al., 2001).(Bray et al., 2002)(Feldmann et al., 2001) Uncoated virus Function: . Virus entry is probably receptor-mediated followed by fusion and uncoating, two steps which have not yet been examined (Feldmann and Kiley, 1999).(Feldmann2) L protein Function: Enzyme. Two other proteins present in lower copy number within the virion, VP35 and the RNA-dependent RNA polymerase, or L protein, associate with VP30 and NP to make up the Ebola replication complex (Bray and Paragas, 2002). The RNA-dependent RNA polymerase or L protein is the largest and least abundant viral protein in both the virion and in infected cells (Peters et al., 1996).(Bray et al., 2002)(Peters) Replication complex Function: . The ribonucleoprotein (RNP) complex in the virion core, made up of the RNA genome and its encapsidating proteins, VP30 and NP, is linked by matrix proteins to the glycoprotein (GP)-bearing lipid envelope derived from the host cell membrane (Bray and Paragas, 2002). Two other proteins present in lower copy number within the virion, VP35 and the RNA-dependent RNA polymerase, or L protein, associate with VP30 and NP to make up the Ebola replication complex (Bray and Paragas, 2002). Genomes of filoviruses consist of a single negative-stranded linear RNA molecule. The RNA is noninfectious, does not contain a poly(A) tail, and upon entry into the cytoplasm of host cells is transcribed to generated polyadenylated subgenomic mRNA species (Feldmann and Kiley, 1999). Filovirus transcription and replication take place in the cytoplasm of infected cells (Feldmann and Kiley, 1999).(Bray et al., 2002)(Feldmann2) Negative sense genome Function: . Genomes of filoviruses consist of a single negative-stranded linear RNA molecule. The RNA is noninfectious, does not contain a poly(A) tail, and upon entry into the cytoplasm of host cells is transcribed to generated polyadenylated subgenomic mRNA species (Feldmann and Kiley, 1999). Filovirus transcription and replication take place in the cytoplasm of infected cells (Feldmann and Kiley, 1999).(Feldmann2) NP mRNA Function: . Transcription by the viral RNA-dependent RNA polymerase initiates at the 3' end of the genome, resulting in synthesis of a leader RNA and seven polyadenylated mRNAs. Accumulation of the first two proteins encoded at the 3' end of the genome (NP and VP35) in some way triggers a switch to production of full-length, positive-sense `antigenomes', which serve, in turn, as templates for genome synthesis (Bray and Paragas, 2002). The nucleoprotein (NP) is encoded by gene 1 at the extreme 3' end of the linear unsegmented RNA genome (Feldmann and Kiley, 1999).(Bray et al., 2002)(Feldmann2) VP35 mRNA Function: . Transcription by the viral RNA-dependent RNA polymerase initiates at the 3' end of the genome, resulting in synthesis of a leader RNA and seven polyadenylated mRNAs. Accumulation of the first two proteins encoded at the 3' end of the genome (NP and VP35) in some way triggers a switch to production of full-length, positive-sense `antigenomes', which serve, in turn, as templates for genome synthesis (Bray and Paragas, 2002). Virion structural protein 35 (VP35) is encoded by gene 2 (Feldmann and Kiley, 1999).(Bray et al., 2002)(Feldmann2) VP40 mRNA Function: . Virion structural protein 40 (VP40) of filoviruses is encoded by gene 3 (Feldmann and Kiley, 1999).(Feldmann2) GP mRNA Function: . Glycoprotein (GP), encoded by gene 4 of the genome, is the only glycosylated structural protein of virions (Feldmann and Kiley, 1999). The GP is the sole structural protein that makes up the virion surface spikes that mediate virus entry into susceptible host cells through receptor binding (Peters et al., 1996).(Feldmann2)(Peters) sGP mRNA Function: . Filoviral glycoproteins are encoded by gene 4 (GP gene) of the non-segmented, negative-stranded RNA genome (Feldmann and Kiley, 1999). In the case of Ebola, but not Marburg virus, the primary product encoded by the GP gene is a truncated protein lacking a C-terminal hydrophobic membrane anchor. This `soluble GP' (sGP) is released from infected cells (Bray and Paragas, 2002).(Feldmann2)(Bray et al., 2002) VP30 mRNA Function: . Virion structural protein 30 (VP30) is encoded by gene 5 of filoviruses and is intimately associated with the RNP complex (Feldmann and Kiley, 1999).(Feldmann2) VP24 mRNA Function: . Virion structural protein 24 (VP24) is encoded by gene 6 of filoviruses (Feldmann and Kiley, 1999). Recent studies have demonstrated that cotransfection of 293T cells with NP, VP35, and VP24 supported capsid formation, and omission of any one of these three genes abolished the effect, demonstrating that they are necessary and sufficient for viral particle formation (Huang et al., 2002).(Feldmann2)(Huang et al., 2002) L mRNA Function: . The large (L) protein is encoded at the 5' end of the linear genome (Feldmann and Kiley, 1999).(Feldmann2) Positive sense genome Function: . Transcription by the viral RNA-dependent RNA polymerase initiates at the 3' end of the genome, resulting in synthesis of a leader RNA and seven polyadenylated mRNAs. Accumulation of the first two proteins encoded at the 3' end of the genome (NP and VP35) in some way triggers a switch to production of full-length, positive-sense `antigenomes', which serve, in turn, as templates for genome synthesis (Bray and Paragas, 2002).(Bray et al., 2002) Negative sense genome Function: . Transcription by the viral RNA-dependent RNA polymerase initiates at the 3' end of the genome, resulting in synthesis of a leader RNA and seven polyadenylated mRNAs. Accumulation of the first two proteins encoded at the 3' end of the genome (NP and VP35) in some way triggers a switch to production of full-length, positive-sense `antigenomes', which serve, in turn, as templates for genome synthesis (Bray and Paragas, 2002).(Bray et al., 2002) NP protein Function: . Transcription by the viral RNA-dependent RNA polymerase initiates at the 3' end of the genome, resulting in synthesis of a leader RNA and seven polyadenylated mRNAs. Accumulation of the first two proteins encoded at the 3' end of the genome (NP and VP35) in some way triggers a switch to production of full-length, positive-sense `antigenomes', which serve, in turn, as templates for genome synthesis (Bray and Paragas, 2002).NP is the primary structural protein associates with filovirus nucleocapsids (Peters et al., 1996). Recent studies have demonstrated that cotransfection of 293T cells with NP, VP35, and VP24 supported capsid formation, and omission of any one of these three genes abolished the effect, demonstrating that they are necessary and sufficient for viral particle formation (Huang et al., 2002).(Bray et al., 2002)(Peters)(Huang et al., 2002) VP35 protein Function: . Transcription by the viral RNA-dependent RNA polymerase initiates at the 3' end of the genome, resulting in synthesis of a leader RNA and seven polyadenylated mRNAs. Accumulation of the first two proteins encoded at the 3' end of the genome (NP and VP35) in some way triggers a switch to production of full-length, positive-sense `antigenomes', which serve, in turn, as templates for genome synthesis (Bray and Paragas, 2002).Recent studies have demonstrated that cotransfection of 293T cells with NP, VP35, and VP24 supported capsid formation, and omission of any one of these three genes abolished the effect, demonstrating that they are necessary and sufficient for viral particle formation (Huang et al., 2002).(Bray et al., 2002)(Huang et al., 2002) VP40 protein Function: . VP40 facilitates the formation of hollow tubular membranes that may facilitate the formation of the surrounding envelope, but does not contribute to the generation of the filamentous viral capsid (Huang et al., 2002). The VP40 protein of Ebola virus is the primary matrix protein and the most abundant virion component (Han et al., 2003).(Huang et al., 2002)(Han et al., 2003) pre-GP protein Function: . Glycoprotein (GP) is the only glycosylated structural protein of virions (Feldmann and Kiley, 1999). The GP is the sole structural protein that makes up the virion surface spikes that mediate virus entry into susceptible host cells through receptor binding (Peters et al., 1996).(Feldmann2)(Peters) pre-sGP protein Function: . In the case of Ebola, but not Marburg virus, the primary product encoded by the GP gene is a truncated protein lacking a C-terminal hydrophobic membrane anchor. This `soluble GP' (sGP) is released from infected cells (Bray and Paragas, 2002).(Bray et al., 2002) VP30 protein Function: . Ebola virus VP30 is an essential activator of viral transcription. In viral particles, VP30 is closely associated with the nucleocapsid complex. A conspicuous structural feature of VP30 is an unconventional zinc-binding Cys(3)-His motif comprising amino acids 68 to 95 (Modrof et al., 2003).(Modrof et al., 2003) VP24 protein Function: . The VP24 protein of Ebola virus is believed to be a secondary matrix protein and minor component of virions. In contrast, the VP40 protein of Ebola virus is the primary matrix protein and the most abundant virion component. VP24 possesses structural features commonly associated with viral matrix proteins and that VP24 may have a role in virus assembly and budding (Han et al., 2003).(Han et al., 2003) L protein Function: Enzyme. The L protein is regarded as an RNA-dependent RNA polymerase (Feldmann and Kiley, 1999). As with other negative-strand RNA viruses, the RNA-dependent RNA polymerase of L protein of filoviruses is the largest and least abundant viral protein in both the virion and in infected cells (Peters et al., 1996).(Feldmann2)(Peters) pre-GP protein Function: . An N-glycosylated precursor form of GP (pre-GP), is found in the endoplasmic reticulum (Jeffers et al., 2002).(Jeffers et al., 2002) pre-sGP protein Function: . The primary gene product of the Ebola virus GP gene is a secreted GP, cleaved to generate secreted GP (sGP) and delta peptide (Jeffers et al., 2002). pre-sGP undergoes several co- and post-translational processing events, such as signal peptide cleavage, glycosylation, oligomerization, and proteolytic cleavage. The limiting step during maturation and transport seems to be oligomerization in the endoplasmic reticulum (Feldmann et al., 2001).(Jeffers et al., 2002)(Feldmann et al., 2001) pre-GP protein Function: . pre-GP is processed to a fully glycosylated uncleaved form, GP0, in the Golgi apparatus. Trafficking to the Golgi apparatus also leads to the addition of O-linked glycans (Jeffers et al., 2002).(Jeffers et al., 2002) pre-sGP protein Function: . After oligomerization, pre-sGP is transported into the Golgi compartments where glycosylation is completed and post-translational cleavage into sGP and a small peptide, designated delta peptide, occurs. Cleavage is mediated by furin (Feldmann et al., 2001).(Feldmann et al., 2001) GP1 protein Function: . In the trans-Golgi apparatus, GP0 is cleaved by the convertase furin to generate GP1, whose role appears to involve receptor binding, and transmembrane GP2. These two subunits are linked by disulfide bonding (Jeffers et al., 2002). GP1 is highly glycosylated with N-linked and O-linked glycans. Glycosylation contributes approximately half of the mass of GP1, and O-linked glycans confer a mucin-like property to its C terminus (Jeffers et al., 2002).(Jeffers et al., 2002) GP2 protein Function: . In the trans-Golgi apparatus, GP0 is cleaved by the convertase furin to generate GP1, whose role appears to involve receptor binding, and transmembrane GP2. These two subunits are linked by disulfide bonding (Jeffers et al., 2002). GP2 contains a sequence of several, uncharged hydrophobic amino acids at a distance of 22 (Ebola virus) or 91 (Marburg virus) amino acids from the cleavage site and which bears some structural similarity to the fusion peptides of retroviruses (Feldmann et al., 2001). GP2 also contains N-linked glycans with two predicted N-linked sites but does not appear to contain O-linked glycans (Jeffers et al., 2002).(Jeffers et al., 2002)(Feldmann et al., 2001) Delta peptide Function: . The small cleavage product of pre-sGP, delta peptide, varies in length between 40 and 48 amino acids for the different Ebola viruses. Its molecular mass of about 10-14 kDa is significantly larger than the one predicted from the amino acid sequence (about 4.7 kDa). This difference in size is due to the attachment of several O-glycans that carry terminal sialic acids. In this respect, it differs from sGP, which seems mainly to carry N-linked carbohydrates (Feldmann et al., 2001).(Feldmann et al., 2001) sGP protein Function: . After oligomerization, pre-sGP is transported into the Golgi compartments where glycosylation is completed and post-translational cleavage into sGP and a small peptide, designated delta peptide, occurs. Cleavage is mediated by furin, which is also responsible for the cleavage of pre-GP (Feldmann et al., 2001).(Feldmann et al., 2001) Furin Function: . >Furin belongs to the proprotein convertases, a family of subtilisin-like eukaryotic endoproteases. These enzymes are differentially expressed in cells and tissues, and they display similar by not identical specificity for basic motifs, such as RXK/RR, at the cleavage site of their substrates. Furin is expressed inmost cells and is localized predominantly in the trans Golgi network. Furin appears to be the key enzyme in virus activation. It is also noteworthy that furin, although ubiquitous, is particularly rich in hepatocytes and endothelial cells which are both prime targets of Ebola virus. These observations stress the importance of furin as a processing enzyme of GP (Volchkov, 1999). After oligomerization, pre-sGP is transported into the Golgi compartments where glycosylation is completed and post-translational cleavage into sGP and a small peptide, designated delta peptide, occurs. Cleavage is mediated by furin, which is also responsible for the cleavage of pre-GP (Feldmann et al., 2001).(Volchkov3)(Feldmann et al., 2001) GP1/2 protein Function: . A special arrangement of cysteine residues in the GP1/2 molecules allows the formation of an intramolecular disulphide bridge between the two cleavage products. This suggests a stem region consisting of GP1 and GP2 and a crown-like domain on the top formed by GP1 that carries the mass of the carbohydrate side chains. The mature transmembrane glycoprotein is a trimer comprising disulphide-bonded GP1/2 molecules. The mature transmembrane glycoprotein forms spikes without the need for other viral proteins (Feldmann et al., 2001).GP1/2 is the virion form of GP and it is also present in cells, presumably in the trans Golgi network and on the cell surface (Volchkov, 1999).(Feldmann et al., 2001)(Volchkov3) GP1/2 protein Function: . The mature envelope glycoprotein GP1/2 is anchored in the membrane by a carboxy-terminal hydrophobic domain of GP2. The middle region of GP1/2 is variable, extremely hydrophilic and carries the bulk of N- and O-glycans, which account for more than one-third of the molecular mass of the mature protein. Oligosaccharide side chains differ in their terminal sialylation patterns. Two carboxy-terminal cysteine residues are acylated. GP2 contains a sequence of several uncharged, hydrophobic amino acids at a distance of 22 (EBOV) or 91 (MBGV) amino acids from the cleavage site and which bears some structural similarity to the fusion peptides of retroviruses. The special arrangement of the cysteine residues in the GP1/2 molecules allows the formation of an intramolecular disulphide bridge between the two cleavage products. This suggests a stem region consisting of GP1 and GP2 and a crown-like domain on the top formed by GP1 that carries the mass of the carbohydrate side chains. It can be assumed that cysteine residue 53 is also critical for maintaining the structure of GP1/2. The mature transmembrane glycoprotein is a trimer comprising disulphide-bonded GP1/2 molecules (Feldmann et al., 2001).(Feldmann et al., 2001) GP1 protein Function: . During maturation, GP1 is partly shed in monomeric form after the release of its disulphide linkage to the transmembrane subunit GP2 (Feldmann et al., 2001). This free GP1 is shed in a nonvirion-bound form and has been hypothesized to be pathogenic (Chan et al., 2000).(Feldmann et al., 2001)(Chan et al., 2000) Delta peptide Function: . Delta peptide is secreted from cells but this process seems not to be as efficient as the secretion of sGP (Feldmann et al., 2001).(Feldmann et al., 2001) sGP protein Function: . Due to a lack of a transmembrane anchor, sGP is secreted efficiently from infected cells (Feldmann et al., 2001).(Feldmann et al., 2001) Viral capsid Function: . The assembly of new viral particles occurs on the inner surface of the plasma membrane, where VP24 and VP40 apparently associate both with new RNPs and with the cytoplasmic tail of GP2 (Bray and Paragas, 2002).(Bray et al., 2002) Budding virus Function: . Nascent virions become enveloped by the GP-bearing lipid bilayer and exit the cell through budding (Bray and Paragas, 2002). New data demonstrate the compartmentalization of Ebola and Marburg viral proteins in lipid rafts during viral assembly and budding (Bavari et al., 2002).(Bray et al., 2002)(Bavari et al., 2002) Virion Function: . The complete replication cycle takes approximately 12 hours. As for many other viruses, filovirus replication triggers a cascade of reactions in infected cells, including the de novo production of type I interferon (IFN-/), which collectively constitute the innate antiviral response. At the same time, certain viral proteins apparently suppress some of these antiviral mechanisms, giving the virus an advantage over its host. The ability of filoviruses to overcome initial defensive barriers and rapidly disseminate may be an essential factor in their virulence (Bray and Paragas, 2002).(Bray et al., 2002)