Fig. 3

Involvement of the gp120 β20–β21 element in regulation of HIV-1 Env conformational transitions. a, b Effect of single-residue changes in the gp120 β20–β21 hairpin on the sensitivity of HIV-1_JR-FL to neutralization by the V3-directed 19b antibody a and by sCD4 b. Changes that increased HIV-1 susceptibility to the specified ligand are shown in blue and all others in red. Residues that contact CD4 are indicated with an asterisk. c Phenotypes associated with gp120 β20-β21 residues. Trp 427 could not be tested due to the low level of replication of the W427A and W427F viruses. d Average IC₅₀ values of inhibition of HIV-1_JR-FL with the β20–β21 changes listed in a and b by conformation-sensitive Env ligands. Reported units are μg ml⁻¹ for 19b, 17b, 902090, and 830 A, and nM for sCD4 and T20; sCD4 binding to the cell-surface Env is normalized to the WT Env values. Reported values for sCD4 inhibition were normalized for sCD4 binding. When IC₅₀ values were above the tested concentrations, the highest concentration tested is shown in blue letters and is underlined. Values that were significantly below or above the ones obtained for WT HIV-1_JR-FL are highlighted with blue and red backgrounds, respectively. e Relationships between the effect of changes in residue 435 on the sensitivity of HIV-1_JR-FL to sCD4 and the polarity, contact energy (in RT units, R = universal gas constant and T = temperature)⁴⁸, and buriability⁴⁹ for each amino acid change. f The effect of changes in residue 422 (left) and residue 435 (right) on the sensitivity of HIV-1_JR-FL to the V3-directed 19b antibody. P values were calculated using a one-sample t test (f, left), a Mann–Whitney test for the difference between the groups (e, left and f, right), or Spearman correlation (e, middle and right). Results shown are the average of those obtained in two or three independent experiments (see also Supplementary Fig. 7). WT, wild-type