Figure 3: A likely arrangement of the HIV-1 gp120 glycoproteins in a trimeric complex.

The gp120 core was organized into a trimeric array, based on the criteria discussed in the text. The perspective is from the target-cell membrane, like that in Fig. 1c. The CD4-binding pockets are indicated by black arrows, and the conserved chemokine-receptor-binding regions are in red. Areas shaded in light green indicate the more variable, glycosylated surfaces of the gp120 cores. The approximate locations of the 2G12 epitopes are indicated by blue arrows; those of the V3 loops (yellow) and V4 regions (green) are indicated. The positions of the V5 regions (green) and some complex-carbohydrate addition sites (asparagines 276, 463, 356, 397 and 406) (blue dots) are shown. The approximate locations of the large V1/V2 loops, centred on the known positions of the V1/V2 stems, are indicated (green). On one of the gp120 subunits, the positions of the ℒD and ℒE loops are indicated. The distance of each of the gp120 monomers from the 3-fold symmetry axis is arbitrary.