(A) The pre-fusion state of the LASV HR1 (yellow) and HR2 (blue) trimers that exist independently but are connected by the T-loop (green). No helical core is present with the trimers oriented nearly perpendicular to the threefold axis (PDB: 5VK2). (B) In the post-fusion state, the HR1, HR2, and T-loop unravel and reorient to form the characteristic coiled-coil/6HB. A central trimer of HR1 is surrounded by three HR2. Each monomer is connected by a T-loop (PDB: 5OMI). (C) A monomer of the coiled-coil is presented with the residues that form salt bridges indicated in black. (D) A surface model of the coiled-coil (PDB: 5OMI). The hydrophobic interactions (red) between adjacent HR1 and HR2 monomers of the 6HB form a core that is further stabilized by salt bridges (black). (E) The sequence of the LASV HRs as connected by the T-loop. Residues that form salt bridges are shown in black and linked to their corresponding ionic partner, while residues involved in the hydrophobic core are shown in red.