Fig 2.

Solution small-angle X-ray scattering structures for full-length gp120 monomer. (A) SAXS pattern for glycosylated SF162 clade B gp120 monomer. Solid black line represents the calculated SAXS pattern for a typical DAMMIN reconstruction. Inset shows the Guinier fit. (B) Corresponding P(r) pairwise distance distribution plot. Black lines represent the calculated SAXS patterns for the modeled structures. (C) “Averaged” SAXS structures for full-length, glycosylated gp120 monomer, shown as an envelope drawn over the averaged, filtered DAMMIN structure (see Fig. S2 in the supplemental material). Structures for gp120 core with N-/C-terminal extensions and intact V3 loop (PDB 3JWD and 2B4C; blue) are fitted into the SAXS density. The CD4 binding site contact residues are shown in orange. The position of the V1/V2 stem (cyan) in the CD4-bound conformation reflected in the CD4-bound gp120 core crystal structures does not fit within the SAXS envelope for unliganded full-length gp120. (D) The V1/V2 loop structure from the crystallographically determined complex with bNAb PG9 (PDB 3U4E; cyan spheres) occupies approximately the same volume of the crest as suggested by the SAXS shape reconstructions. See also Movie S1 in the supplemental material.