Retrovirus envelope domain at 1.7 angstrom resolution.

We report the crystal structure of an extraviral segment of a retrovirus envelope protein, the Moloney murine leukemia virus (MoMuLV) transmembrane (TM) subunit. This segment, which comprises a region of the MoMuLV TM protein analogous to that contained within the X-ray crystal structure of low-pH converted influenza hemagglutinin, contains a trimeric coiled coil, with a hydrophobic cluster at its base and a strand that packs in an antiparallel orientation against the coiled coil. This structure gives the first high-resolution insight into the retrovirus surface and serves as a model for a wide range of viral fusion proteins; key residues in this structure are conserved among C- and D-type retroviruses and the filovirus ebola.