Fig 1. Z1800M and R66M trimers.

(A) Linear representations of the R66M NFL and the Z1800M UFO Env trimers are shown. Cysteine residues are indicated along the top; the (G₄S)₂ linker is indicated by a black dashed line; the optimized gp41 region in the UFO is indicated by a green dashed line; key amino acid substitutions with HXB2 numbering are indicated along the Env open reading frame and are color-coded to indicate their putative contribution to stabilization. The CD5 leader sequence is also shown. (B) Size exclusion chromatography profiles are shown for the BG505 NFL trimer as a process control, the R66M NFL trimer, and the Z1800M UFO trimer. The fractions corresponding to the trimeric proteins are shaded.