Fitting of gp120 X-ray structures into NL4-3 and NL4-3/ADA gp140 density maps. Automated fitting of a gp120 X-ray structure (pdb 2NY7) into NL4-3 (grey) and NL4-3/ADA gp140 density maps (cyan), viewed from top (A) and side view (B). In the bottom row, the 3D model of NL4-3 gp140 is shown with the locations of the V3 loop and the CD4 binding site indicated with green and yellow balls, respectively. Magenta balls represent the N- and C-terminal stumps of gp120. The bridging sheets are colored in blue.