Mapping of the HIV-1 gp120 core epitope. (A) Heat map summarizes the binding of the different anti-core antibodies and b12 to gp120 alanine mutants. Red and orange fields indicate <60% binding, whereas yellow shows no difference compared with the WT gp120 control. The mapping of the anti-core epitope has been confirmed by three independent experiments. (B) Surface diagram of gp120 (PDB ID: 3DNO; Liu et al., 2008) showing the CD4bs (blue), the CD4is (gray), the b12 binding sites (yellow), and the core epitope (green). Residues that distinguished between the anti-CD4bs epitope and anti-core epitope are highlighted with circles. (C) Diagram shows the apparent binding of anti-core antibodies and b12 to mutant gp120_{D474AM475AR476A} relative to gp120 WT in percent. The red star indicates binding to D368A. (D) Venn diagram summarizes the sensitivity for anti-core antibodies binding to D474A, M475A, and R476A. (E) Ribbon diagram of gp120 (PDB ID: 3DNO; Liu et al., 2008) shows the CD4bs (blue), the CD4is (gray), and the core epitope (green).