Impact of the R77Q mutation of Vpr on the conformation of Vpr and the interaction between Vpr and ANT. (a) Representation of wild-type (R77) Vpr and R77Q Vpr. Three amphipathic helices (shown in red and yellow) are linked by turns (green) and flexible loops (gray). The mitochondriotoxic domain of Vpr has been marked in yellow. Only the side chain of amino acid 77 is shown. (b) View of the arginine residues (R73, R77, R80) within the mitochondriotoxic domain of Vpr (yellow) and the aromatic residues of ANT (F109, W111, Y113 and/or F114) involved in cation-π interactions, as calculated by molecular modeling (10). The inner mitochondrial membrane (dark blue) is indicated to facilitate the topological orientation of the third loop (residues 104–116) of ANT. C, carboxy terminus; N, amino terminus; L134 and R72 are amino residues of ANT.