Fig. 1

The crystal structure of the Bcl-xL/HBx-aa113–135 complex. a Cartoon representation of structural comparison of Bcl-xL/HBx-BH3 motif with Bcl-xL at free form (PDB ID 5B1Z). The structures of Bcl-xL/HBx-BH3 motif and Bcl-xL at free form are colored in green and cyan, respectively. The bound HBx-BH3 peptide is shown in carton mode and colored in wheat. The key residues involved in tight interactions are highlighted in stick mode. b Cartoon representation of structural comparison of Bcl-xL/Bim-BH3 motif (PDB ID 1PQ1¹³) with Bcl-xL at free form (PDB ID 1R2D⁴⁶). The structure of Bcl-xL/Bim-BH3 motif is colored in magenta. The bound Bim-BH3 peptide is shown in carton mode and colored in red. The corresponding key residues involved in tight interactions are highlighted in stick mode. c Electrostatic potential surface view of Bcl-xL/HBx-BH3 motif complex. The bound HBx-BH3 motif forms a short, two-helical-turn α-helix snuggling into a small hydrophobic pocket, which is partially preformed. The key residues involved in hydrophobic interactions are indicated. d Electron densities around the HBx W120 residue are shown in red mesh contours. e Electrostatic potential surface view of Bcl-xL/Bim-BH3 motif complex. The bound Bim-BH3 motif forms a continuous long α-helix fitting into the big groove formed by Bcl-xL upon Bim binding. The corresponding key residues involved in interactions are indicated. f Electrostatic potential surface view of Bcl-xL at free form. A preformed small groove/pocket at the bottom of the surface is observed. d–f were made by pymol using the default parameters provided. The map was calculated using Fo-Fc coefficients and phases from the refined structure, but with the residues omitted from the Fc calculation. The map is contoured at 3σ. The side chains of HBx-BH3 and Bcl-xL are shown in stick model. HBx and Bcl-xL molecules are colored in wheat and green, respectively