heptad repeat 1-heptad repeat 2 region (ectodomain) of the transmembrane subunit of Rous sarcoma virus (RSV), 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 Rous sarcoma virus gp37, Avian leukosis virus subgroup J (ALV-J) envelope protein, and the envelope proteins of various ERVs, including those belonging to the ev/J (or EAV-HP) family of chicken ERVs, such as ev/J 4.1 Rb. ALV-J is a recently emerged avian pathogen, the causative agent of myeloid leukosis in meat-type chicken. ERVs are likely to originate from ancient germ-line infections by active retroviruses. ALV-J may have emerged from a recombination event between an unknown ALV and an EAV-HP ERV. 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.
Comment: The conformation of Ebola virus HR1 changes significantly in the pre-fusion (three-helix bundle) and post-fusion (six-helix bundle) conformations of the HR1-HR2 region.
Jiyao W et al.(2023). "The conserved domain database in 2023.",