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TCIDNameDomainKingdom/PhylumProtein(s)
1.G.9.1.1









HERV-W_7q21.2 provirus ancestral Env polyprotein (ENV-W; gPr73; enverin; syncytin-1, HERV-7q envelope protein) (Blond et al., 1999; Mi et al., 2000).  This endogenous retroviral envelope protein, encoded within the human genome, has retained its original fusogenic properties and participates in trophoblast fusion and the formation of a syncytium during placenta morphogenesis. It may induce fusion through binding of SLC1A4 and SLC1A5 (Blond et al. 2000; Lavillette et al. 2002; Sugimoto et al. 2013. Syncytin-1 interacts with the ASCT2 receptor (Štafl et al. 2021). It also participates in virus-free extracellular vesicle cargo loading and delivery (see TC# 8.A. 40.1.19) (Lavillette et al. 2002; Sugimoto et al. 2013. Syncytin-1 interacts with the ASCT2 receptor (Štafl et al. 2021). It also participates in virus-free extracellular vesicle cargo loading and delivery (see TC# 8.A. 40.1.19) (Bui et al. 2023).

 

Eukaryota
Metazoa, Chordata
HERV-W_7q21.2 of Homo sapiens (Q9UQF0)
1.G.9.1.2









Syncytin 2 of 538 aas.  Syncytins maintain cell-cell fusogenic activity based on ENV: gene-mediated viral cell entry but promote fusion of various cells during development in humans (Soygur and Sati 2016).

Eukaryota
Metazoa, Chordata
Syncytin 2 of Homo sapiens
1.G.9.2.1









Envelope glycoprotein, Env, of 654 aas and 3 TMSs, one N-terminal, one C-terminal and one at about residue 473.

Viruses
Pararnavirae, Artverviricota
Env of porcine endogenous retrovirus A
1.G.9.2.2









The human T-lymphotropic virus type 1 (HTLV-1) glycoprotein gp21 of 121 aas and containing the N-terminal 25 aa fusion peptide with a single TMS.

Viruses
Pararnavirae, Artverviricota
gp21 of the human T-lymphotropic virus type 1 (HTLV-1)
1.G.9.2.3









The Human T-cell leukemia virus 1, HTLV-1, of 488 aas and 2 or 3 TMSs, N- and C-terminal with a possible additional TMS at residue 320. The glycine-rich region of this transmembrane protein is involved in membrane fusion. It is a class I viral fusion protein (Wilson et al. 2005). The N-terminal fusion peptide initiates virus-cell membrane fusion. The fusion peptide is linked to the coiled-coil core through a conserved sequence that is rich in glycines. Wilson et al. 2005 investigated the functional role of the glycine-rich segment, Met-326 to Ser-337, of gp21. Alanine substitution for the hydrophobic residue Ile-334 caused a 90% reduction in cell-cell fusion activity without a detectable effect on the lipid-mixing and pore forming phases of fusion. Retroviral glycoprotein fusion thus appears to require flexibility within the glycine-rich segment and hydrophobic contacts mediated by this segment (Wilson et al. 2005).

 

Viruses
Pararnavirae, Artverviricota
HTLV-1 of T-cell leukemia virus 1
1.G.9.2.4









Envelope glycoprotein of 259 aas with 12 N-terminal TMS, Env.

Viruses
Pararnavirae, Artverviricota
Env of Human T-cell leukemia virus 2 (HTLV-2)
1.G.9.2.5









Envelope glycoprotein of 214 aas (partial), Gp30, with 2 TMSs, one at the N-terminus, and one at residues 140 - 160.

Viruses
Pararnavirae, Artverviricota
Gp30 of bovine leukemia viru
1.G.9.2.6









Envolope glycoprotein of 341 aas and 3 TMSs, one N-terminal and two C-terminal, gPr72. Three YXXL sequences of a Bovine Leukemia Virus TEnv transmembrane protein are independently required for fusion activity by controlling expression on the cell membrane (Matsuura et al. 2019). The fusion peptide mediates fusion of the viral envelop with the cell membrane (Meher and Chakraborty 2020).

Viruses
Pararnavirae, Artverviricota
Env protein of bovine leukemia virus