Fig. 4.

gp41 subunit in the Env trimer. (A) Cryo-EM map of the three gp41 subunits in the Env trimer, viewed from an angle of ∼30° with respect to the viral membrane. (B) gp41 membrane-interactive region viewed from a perspective parallel to the viral membrane. (C) gp41 ectodomain, viewed from the perspective of the virus. The torus-like topology of the three gp41 subunits in the Env trimer is evident from this perspective. (D) gp41 ectodomain, viewed from a perspective parallel to the viral membrane. (E) Comparison of the gp41 ectodomain in the unliganded precursor state and the postfusion state with respect to the tertiary organization of helices. The perspective is identical to that shown in D, with a reduction in scale. For simplicity, only one of the three gp41 glycoprotein subunits in the Env trimer is depicted.