Fig. 1: Structures of the Tri FPPR.1 and Tri FPPR.2 Env conformers.

a. The two schematic diagrams on the left indicate the nomenclature of the gp120 chains (chains A, C and E) and gp41 chains (chains B, D and F). Except where noted, the color scheme for the Env protomers and subunits will be used throughout the manuscript. The schematic diagram on the left is a view down the Env trimer axis, from the perspective of the membrane of the virus or expressing cell. The opening angle between Protomer 1 and Protomer 3 is less than 120 degrees in these asymmetric trimers. The schematic diagram on the right is a side view, with the gp41 subunits at the top and the gp120 subunits at the bottom of the images. On the right, two 5 Å-filtered Tri FPPR.2 density maps are shown, from the same perspectives used for the schematic diagrams. The α9 helix and MPER from Protomer 1 (red ribbons) interacts with the FPPR-HR1_N structures (blue ribbons) of the clockwise protomer (Protomer 3), when viewed from the perspective of the viral/cell membrane. b The Tri FPPR.1 and Tri FPPR.2 density maps are colored and shown from the same perspectives as in (a). c The Tri FPPR.1 and Tri FPPR.2 models are shown, fitted into the respective maps that were filtered to 5-Å resolution.