FIG 1.

Schematic representations of Env proteins. Linear representations of the 92UG037.8- and CZA97.012-based Env proteins used in these studies are shown, with variable and conserved domains (conserved domain 1 [C1] to C5 and variable domain 1 [V1] to V5) and the positions and classifications of glycan moieties indicated. The following elements are on all the constructs: heptad repeat 1 (HR1), heptad repeat 2 (HR2), and membrane-proximal external region (M). The full-length gp160 protein, not made in this study, contains transmembrane (TM) and cytoplasmic domains that are absent from the soluble proteins. The SOSIP.664-His constructs contain the intersubunit (gp120-gp41_ECTO) disulfide bond (A501C plus T605C), the I559P substitution, and R6 cleavage-enhancing change, all shown in red. Compared to the 92UG037.8 virus sequence, the corresponding SOSIP.664-His trimer also contains an amino acid substitution, I535M, shown in blue. Similarly, the additional substitutions in the CZA97.012 SOSIP.664-His trimer, also shown in blue, are L535M and Q567K. These changes are not present in the corresponding uncleaved gp140_UNC-Fd-His proteins. The Foldon (Fd) domains present in the uncleaved gp140s are black, and the His tags are yellow. The 20-residue flexible linkers (FL20s) added to the 92UG037.8 gp140-FL20, gp140-FL20-IP, and gp140-FL20-SOSIP constructs are red, as are the IP and SOSIP changes present in the latter two constructs.