Top panels show (A) CD4 binding loop, (C) HC, (E) LC contacts in superimposed NIH45-46GL/426c.TM1△V1-3 and NIH45-46MAT/93TH057 (PDB 3U7Y) complexes. Bottom panels show (B) CD4-binding loop, (D) HC, (F) LC contacts in superimposed 3BNC60GL/426c.TM4△V1-3 and 3BNC117MAT/93TH057 (PDB 4JPV) complexes. Protein backbones are shown as wire diagrams, interacting residues are shown as stick representations (red, oxygen; blue, nitrogen). Yellow dashed lines indicate putative hydrogen bonds (distance < 3.5 Å, A-H–D angle > 90°). Ab coloring: blue, NIH45-46GL HC; light blue, NIH45-46GL LC; orange, NIH45-46MAT HC; yellow, NIH45-46MAT LC; green, 3BNC60GL HC; light green, 3BNC60GL LC; purple, 3BNC60MAT HC; light pink 3BNC60MAT LC. gp120 coloring: blue, CD4-binding loop; green, loop D; teal, loop V5. (E, F) Interacting residues of the C” strand of Fab HCs and the CD4-binding loop of gp120 (grey) are shown as sticks. The Fab residue numbers are indicated since the amino acid sequence differs at some positions between germline and mature Abs.