Summary: Alphavirus E3 glycoprotein
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Alphavirus Edit Wikipedia article
In biology and immunology, an Alphavirus belongs to group IV of the Baltimore classification of the Togaviridae family of viruses, according to the system of classification based on viral genome composition introduced by David Baltimore in 1971. Alphaviruses, like all other group IV viruses, have a positive sense, single-stranded RNA genome. There are thirty alphaviruses able to infect various vertebrates such as humans, rodents, fish, birds, and larger mammals such as horses as well as invertebrates. Transmission between species and individuals occurs mainly via mosquitoes, making the alphaviruses a member of the collection of arboviruses â€“ or arthropod-borne viruses. Alphavirus particles are enveloped, have a 70 nm diameter, tend to be spherical (although slightly pleomorphic), and have a 40 nm isometric nucleocapsid.
crystal structure of the homotrimer of fusion glycoprotein e1 from semliki forest virus.
|SCOPe||1rer / SUPFAM|
mapping the e2 glycoprotein of alphaviruses
The alphaviruses are small, spherical, enveloped viruses with a genome of a single positive sense strand RNA. The total genome length ranges between 11,000 and 12,000 nucleotides, and has a 5â€™ cap, and 3â€™ poly-A tail. The four non-structural protein genes are encoded in the 5â€² two-thirds of the genome, while the three structural proteins are translated from a subgenomic mRNA colinear with the 3â€² one-third of the genome.
There are two open reading frames (ORFâ€™s) in the genome, non-structural and structural. The first is non structural and encodes proteins (nsP1â€“nsP4) necessary for transcription and replication of viral RNA. The second encodes three structural proteins: the core nucleocapsid protein C, and the envelope proteins P62 and E1 that associate as a heterodimer. The viral membrane-anchored surface glycoproteins are responsible for receptor recognition and entry into target cells through membrane fusion.
The proteolytic maturation of P62 into E2 and E3 causes a change in the viral surface. Together the E1, E2, and sometimes E3, glycoprotein "spikes" form an E1/E2 dimer or an E1/E2/E3 trimer, where E2 extends from the centre to the vertices, E1 fills the space between the vertices, and E3, if present, is at the distal end of the spike. Upon exposure of the virus to the acidity of the endosome, E1 dissociates from E2 to form an E1 homotrimer, which is necessary for the fusion step to drive the cellular and viral membranes together. The alphaviral glycoprotein E1 is a class II viral fusion protein, which is structurally different from the class I fusion proteins found in influenza virus and HIV. The structure of the Semliki Forest virus revealed a structure that is similar to that of flaviviral glycoprotein E, with three structural domains in the same primary sequence arrangement. The E2 glycoprotein functions to interact with the nucleocapsid through its cytoplasmic domain, while its ectodomain is responsible for binding a cellular receptor. Most alphaviruses lose the peripheral protein E3, but in Semliki viruses it remains associated with the viral surface.
Non structural proteins
Four nonstructural proteins (nsP1â€“4) which are produced as a single polyprotein constitute the virus' replication machinery. The processing of the polyprotein occurs in a highly regulated manner, with cleavage at the P2/3 junction influencing RNA template use during genome replication. This site is located at the base of a narrow cleft and is not readily accessible. Once cleaved nsP3 creates a ring structure that encircles nsP2. These two proteins have an extensive interface.
Mutations in nsP2 that produce noncytopathic viruses or a temperature sensitive phenotypes cluster at the P2/P3 interface region. P3 mutations opposite the location of the nsP2 noncytopathic mutations prevent efficient cleavage of P2/3. This in turn affects RNA infectivity altering viral RNA production levels.
The virus has a 60â€“70 nanometer diameter. It is enveloped, spherical and has a positive-strand RNA genome of ~12 kilobases. The genome encodes two polyproteins. The first polyprotein consists of four non-structural units: in order from the N terminal to the C terminal - nsP1, nsP2, nsP3, and nsP4. The second is a structural polyprotein composed of five expression units: from the N terminal to the C terminal - Capsid, E3, E2, 6K and E1. A sub genomic positive strand RNA - the 26S RNA - is replicated from a negative-stranded RNA intermediate. This serves as template for the synthesis of viral structural proteins. Most alphaviruses have conserved domains involved in regulation of viral RNA synthesis.
The nucleocapsid, 40 nanometers in diameter, contains 240 copies of the capsid protein and has a T = 4 icosahedral symmetry. The E1 and E2 viral glycoproteins are embedded in the lipid bilayer. Single E1 and E2 molecules associate to form heterodimers. The E1â€“E2 heterodimers form one-to-one contacts between the E2 protein and the nucleocapsid monomers. The E1 and E2 proteins mediate contact between the virus and the host cell.
Replication occurs within the cytoplasm and virions mature by budding through the plasma membrane, where virus-encoded surface glycoproteins E2 and E1 are assimilated.
These two glycoproteins are the targets of numerous serologic reactions and tests including neutralization and hemagglutination inhibition. The alphaviruses show various degrees of antigenic cross-reactivity in these reactions and this forms the basis for the seven antigenic complexes, 30 species and many subtypes and varieties. The E2 protein is the site of most neutralizing epitopes, while the E1 protein contains more conserved, cross-reactive epitopes.
A study of this taxon suggests that this group of viruses had a marine originâ€”specifically the Southern Oceanâ€”and that they have subsequently spread to both the Old and New World.
There are three subgroups in this genus: the Semliki Forest virus subgroup (Semliki Forest, O'nyong-nyong and Ross River viruses); the eastern equine encephalitis virus subgroup (eastern equine encephalitis and Venezuelan equine encephalitis viruses) and the Sindbis virus subgroup. Sindbis virus, geographically restricted to the Old World, is more closely related to the eastern equine encephalitis subgroup, which are New World viruses, than it is to the Semliki Forest virus subgroup which is also found in the Old World.
The seven complexes are:
- Barmah Forest virus complex
- Eastern equine encephalitis complex
- Eastern equine encephalitis virus (seven antigenic types)
- Middelburg virus complex
- Ndumu virus complex
- Ndumu virus
- Semliki Forest virus complex
- Venezuelan equine encephalitis complex
- Western equine encephalitis complex
Barmah Forest virus is related to the Semliki Forest virus. Middelburg virus, although classified as a separate complex, may be a member of the Semliki Forest virus group.
It seems likely that the genus evolved in the Old World from an insect-borne plant virus.
Sindbis virus may have originated in South America. The equine encephalitis viruses and the Sindbis virus are related.
The Old World and New World viruses appears to have diverged between 2000 and 3000 years ago. Divergence between the Venezuelan equine encephalitis virus and the eastern equine virus appears to have been ~1400 years ago.
The fish infecting clade appears to be basal to the other species.
The southern elephant seal virus appears to be related to the Sinbis clade.
Pathogenesis and immune response
|Virus||Human Disease||Vertebrate Reservoir||Distribution|
|Barmah Forest virus||Fever, malaise, rash, joint pain, muscle tenderness||Humans||Australia|
|Chikungunya virus||Rash, arthritis||Primates, humans||Africa, Latin America, India, SE Asia|
|Mayaro virus||Rash, arthritis||Primates, humans||South America|
|O'nyong'nyong virus||Rash, arthritis||Primates, Humans||Africa|
|Ross River virus||Rash, arthritis||Mammals, humans||Australia, South Pacific|
|Semliki Forest virus||Rash, arthritis||Birds||Africa|
|Sindbis virus||Rash, arthritis||Birds||Europe, Africa, Australia|
|Una virus||Rash, arthritis||Primates, humans||South America|
|Eastern equine encephalitis virus||Encephalitis||Birds||Americas|
|Tonate virus||Encephalitis||Humans||South America|
|Venezuelan equine encephalitis virus||Encephalitis||Rodents, horses||Americas|
|Western equine encephalitis virus||Encephalitis||Birds, mammals||North America|
There are many alphaviruses distributed around the world with the ability to cause human disease. Infectious arthritis, encephalitis, rashes and fever are the most commonly observed symptoms. Larger mammals such as humans and horses are usually dead-end hosts or play a minor role in viral transmission; however, in the case of Venezuelan equine encephalitis the virus is mainly amplified in horses. In most other cases the virus is maintained in nature in mosquitoes, rodents and birds.
Alphavirus infections are spread by insect vectors such as mosquitoes. Once a human is bitten by the infected mosquito, the virus can gain entry into the bloodstream, causing viremia. The alphavirus can also get into the CNS where it is able to grow and multiply within the neurones. This can lead to encephalitis, which can be fatal.
When an individual is infected with this particular virus, its immune system can play a role in clearing away the virus particles. Alphaviruses are able to cause the production of interferons. Antibodies and T cells are also involved. The neutralizing antibodies also play an important role to prevent further infection and spread.
Diagnosis, prevention, and control
Diagnoses is based on clinical samples from which the virus can be easily isolated and identified. There are no alphavirus vaccines currently available. Vector control with repellents, protective clothing, breeding site destruction, and spraying are the preventive measures of choice.
Alphaviruses are of interest to gene therapy researchers, in particular the Ross River virus, Sindbis virus, Semliki Forest virus, and Venezuelan equine encephalitis virus have all been used to develop viral vectors for gene delivery. Of particular interest are the chimeric viruses that may be formed with alphaviral envelopes and retroviral capsids. Such chimeras are termed pseudotyped viruses. Alphaviral envelope pseudotypes of retroviruses or lentiviruses are able to integrate the genes that they carry into the expansive range of potential host cells that are recognized and infected by the alphaviral envelope proteins E2 and E1. The stable integration of viral genes is mediated by the retroviral interiors of these vectors. There are limitations to the use of alphaviruses in the field of gene therapy due to their lack of targeting, however, through the introduction of variable antibody domains in a non-conserved loop in the structure of E2, specific populations of cells have been targeted. Furthermore, the use of whole alphaviruses for gene therapy is of limited efficacy both because several internal alphaviral proteins are involved in the induction of apoptosis upon infection and also because the alphaviral capsid mediates only the transient introduction of mRNA into host cells. Neither of these limitations extend to alphaviral envelope pseudotypes of retroviruses or lentiviruses. However, the expression of Sindbis virus envelopes may lead to apoptosis, and their introduction into host cells upon infection by Sindbis virus envelope pseudotyped retroviruses may also lead to cell death. The toxicity of Sindbis viral envelopes may be the cause of the very low production titers realized from packaging cells constructed to produce Sindbis pseudotypes. Another branch of research involving alphaviruses is in vaccination. Alphaviruses are apt to be engineered to create replicon vectors which efficiently induce humoral and T-cell immune responses. They could therefore be used to vaccinate against viral, bacterial, protozoan, and tumor antigens.
- Alphavirus vectors: from protein production to gene therapy, C Smerdou & P Liljestrom, Gene Therapy and Regulation Vol 1 No 1 2000 pp. 33â€“63
- Rayner, Jonathan O; Dryga, Sergey A; Kamrud, Kurt I (2002). "Alphavirus vectors and vaccination". Reviews in Medical Virology. 12 (5): 279â€“296. doi:10.1002/rmv.360. PMID 12211042.
- Chen, R; Mukhopadhyay, S; Merits, A; Bolling, B; Nasar, F; Coffey, LL; Powers, A; Weaver, SC; Ictv Report, Consortium (June 2018). "ICTV Virus Taxonomy Profile: Togaviridae". The Journal of General Virology. 99 (6): 761â€“762. doi:10.1099/jgv.0.001072. PMID 29745869.
- VÃ©nien-Bryan C, Fuller SD (February 1994). "The organization of the spike complex of Semliki Forest virus". J. Mol. Biol. 236 (2): 572â€“83. doi:10.1006/jmbi.1994.1166. PMID 8107141.
- Lescar J, Roussel A, Wien MW, Navaza J, Fuller SD, Wengler G, Wengler G, Rey FA (April 2001). "The Fusion glycoprotein shell of Semliki Forest virus: an icosahedral assembly primed for fusogenic activation at endosomal pH". Cell. 105 (1): 137â€“48. doi:10.1016/S0092-8674(01)00303-8. PMID 11301009.
- Shin G, Yost SA, Miller MT, Elrod EJ, Grakoui A, Marcotrigiano J (2012) Structural and functional insights into alphavirus polyprotein processing and pathogenesis. Proc Natl Acad Sci USA
- Forrester NL, Palacios G, Tesh RB, Savji N, Guzman H, Sherman M, Weaver SC, Lipkin WI (December 2011). "Genome scale phylogeny of the Alphavirus genus suggests a marine origin". J Virol. 86 (5): 2729â€“38. doi:10.1128/JVI.05591-11. PMC 3302268. PMID 22190718.
- Levinson RS, Strauss JH, Strauss EG (1990). "Complete sequence of the genomic RNA of O'nyong-nyong virus and its use in the construction of alphavirus phylogenetic trees". Virology. 175 (1): 110â€“123. doi:10.1016/0042-6822(90)90191-s.
- "ICTV Report Togaviridae".
- Powers AM, Brault AC, Shirako Y, Strauss EG, Kang W, Strauss JH, Weaver SC (November 2001). "Evolutionary relationships and systematics of the alphaviruses". J. Virol. 75 (21): 10118â€“31. doi:10.1128/JVI.75.21.10118-10131.2001. PMC 114586. PMID 11581380.
- LundstrÃ¶m JO, Pfeffer M (November 2010). "Phylogeographic structure and evolutionary history of Sindbis virus". Vector Borne Zoonotic Dis. 10 (9): 889â€“907. doi:10.1089/vbz.2009.0069. PMID 20420530.
- Weaver SC, Hagenbaugh A, Bellew LA, Netesov SV, Volchkov VE, Chang GJ, Clarke DK, Gousset L, Scott TW, Trent DW (November 1993). "A comparison of the nucleotide sequences of eastern and western equine encephalomyelitis viruses with those of other alphaviruses and related RNA viruses". Virology. 197 (1): 375â€“90. doi:10.1006/viro.1993.1599. PMID 8105605.
- Weaver SC, Rico-Hesse R, Scott TW (1992). "Genetic diversity and slow rates of evolution in New World alphaviruses". Curr. Top. Microbiol. Immunol. 176: 99â€“117. PMID 1318187.
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Alphavirus E3 glycoprotein Provide feedback
This protein is found in some alphaviruses as a virion associated spike protein .
Paredes AM, Heidner H, Thuman-Commike P, Prasad BV, Johnston RE, Chiu W; , J Virol 1998;72:1534-1541.: Structural localization of the E3 glycoprotein in attenuated Sindbis virus mutants. PUBMED:9445057 EPMC:9445057
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR002533
Alphaviruses are enveloped RNA viruses that use arthropods such as mosquitoes for transmission to their vertebrate hosts, and include Semliki Forest and Sindbis viruses [ PUBMED:15378043 ]. Alphaviruses consist of three structural proteins: the core nucleocapsid protein C, and the envelope proteins P62 and E1 ( INTERPRO ) that associate as a heterodimer. The viral membrane-anchored surface glycoproteins are responsible for receptor recognition and entry into target cells through membrane fusion. The proteolytic maturation of P62 into E2 ( INTERPRO ) and E3 causes a change in the viral surface. Together the E1, E2, and sometimes E3 glycoprotein "spikes" form an E1/E2 dimer or an E1/E2/E3 trimer, where E2 extends from the centre to the vertices, E1 fills the space between the vertices, and E3, if present, is at the distal end of the spike [ PUBMED:8107141 , PUBMED:9445057 ]. Upon exposure of the virus to the acidity of the endosome, E1 dissociates from E2 to form an E1 homotrimer, which is necessary for the fusion step to drive the cellular and viral membranes together [ PUBMED:11301009 ]. This entry represents the alphaviral E3 glycoprotein. Most alphaviruses lose the peripheral protein E3, but in Semliki viruses it remains associated with the viral surface.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||virion membrane (GO:0055036)|
|viral capsid (GO:0019028)|
|Molecular function||serine-type endopeptidase activity (GO:0004252)|
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Key: available, not generated, — not available.
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|Seed source:||Pfam-B_285 (release 4.0)|
|Number in seed:||3|
|Number in full:||5|
|Average length of the domain:||57.40 aa|
|Average identity of full alignment:||63 %|
|Average coverage of the sequence by the domain:||5.32 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||18|
|Download:||download the raw HMM for this family|
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Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
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Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Alpha_E3_glycop domain has been found. There are 26 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.
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