Orexin-A peptide and the surface complementarity of the two binding modes. (A) Orexin-A from opposite sides. (B, C) TM5-mode. (D, E) TM7-mode. Panels B and D show hydrophobic, and panels C and E hydrophilic surfaces. Receptor surfaces on color scale brown-blue (hydrophobic-hydrophilic), ligand surfaces magenta-green. The receptor surface has been drawn based on the side chain atoms of the residues that have atoms within 4 Å of the peptide ligand.