(a) Homology model of pHtrII-cyt based on the structure of Tsr-cyt. Negatively charged amino acids are shown in red, positively charged amino acids in blue, and hydrophobic amino acids in green. (b) FastContact analysis of each helix in a coiled-coil monomer chain. Amino acids contributing to favorable electrostatic interactions are shown in cyan, those contributing to free energy contacts in orange, and those contributing to both are shown in purple. (c) FastContact analysis of the dimer interface. Colors as in (b), (d). Docking of the two monomeric chains using ClusPro software. Colors from FastContact analysis as in (b), (c).