NBD:TMD communication pathways. For sake of clarity only the residues identified starting from the N-terminal NBD are indicated. First pathway: From adenine → directly or through NBD aromatic residues → ICL1 → ICL4. Second pathway: From ATP phosphates → directly to Q-loop of the same NBD or through ABC signature from the ATP of the facing NBD to the Q-loop → ICL4. The colors of the links between the residues depict the physical nature of their interactions: yellow: hydrophobic, magenta: aromatic-aromatic, cyan: hydrogen bond and blue: electrostatic.