heptad repeat 1-heptad repeat 2 region of the transmembrane subunit of Filoviridae viruses, Ebola virus and Marburg virus, and related domains
This domain subfamily spans both heptad repeats of the glycoprotein (gp)/transmembrane subunit of various endogenous retroviruses (ERVs) and infectious retroviruses, including Ebola virus gp2, Marburg virus gp, and the envelope proteins of various ERVs, including human HERV-R_c7q21.2 (ERV-3). This domain includes an N-terminal heptad repeat, a CKS17-like immunosuppressive region, a CX6C motif that forms an intrasubunit disulfide bond, and a C-terminal heptad repeat. N-terminal to HR1-HR2 region is a fusion peptide (FP), and C-terminal, is a membrane-spanning region (MSR). Viral infection involves the formation of a trimer-of-hairpins structure (three HR1s helices, buttressed by three HR2 helices lying in antiparallel orientation). In this structure, the FP (inserted in the host cell membrane) and MSR (inserted in the viral membrane) are in close proximity. ERVs are likely to originate from ancient germ-line infections by active retroviruses. Some ERVs play specific roles in the host. However, it is unclear whether ERV-3 has a critical biological role: it is expressed in the placenta, but is not fusogenic, has an immunosuppressive domain, but lacks a fusion peptide. Filoviridae, the family of viruses including Ebola and Marburg, may have acquired this domain via horizontal transfer from retroviruses.
Jiyao W et al.(2023). "The conserved domain database in 2023.",