Figure 1.

Strategy and sequences used in the present study.Panel A. Representation of the V1V2 region according to the structure of McLellan et al. [31]. The four β-sheets are indicated by yellow arrows, the unstructured loops V1 and V2 are indicated in red and blue, respectively, whereas the small loop connecting β-sheets B and C is drawn in green. The start of the β-sheet B differed between the two isolates used in McLellan et al. (CAP 45 and ZM109). Here, we considered the minimal size of the β-sheet B, which is the one from the isolate CAP 45. Panel B. Amino acid sequence alignment of the V1V2 region for the isolates used to generate the main five chimeras characterized in this study. Identical residues are in a yellow background, and hyphenations indicate gaps in the alignment. The C residues that define the borders of the V1 and V2 regions are indicated in red. The delimitations of the V1 and V2 regions is given, as a reference, at the bottom of the drawing. The vertical gray bars define the borders of the structural domains defined by McLellan and colleagues [31]. The four β-sheets are indicated as βA, B, C and D, while the region indicated as "connection" corresponds to the mini loop connecting β-sheets B and C (see text for details). Alignments were performed using MUSCLE 3.8 [55]. Panel C. Schematic representation of the chimeric HIV-1 envelopes used in this study. The structure of the HIV-1 envelope gene is given at the top as a reference, with the constant and variable regions of the gp120 region in green and yellow, respectively. The fusion peptide (FP), helix N (HN), helix C (HC), transmembrane domain (TM) and cytoplasmic tail (CT) of the gp41 are indicated in gray.