Macrodipoles of potassium and chloride ion channels as revealed by electronic structure calculations

With the aid of quantum mechanical calculations we investigate the electronic structure of the full length (FL) potassium channel protein, FL-KcsA, in its closed conformation, and the electronic structure of the ClC chloride channel. The results indicate that both ion channels are strongly polarized towards the extracellular region with respect to the membrane mean plane. FL-KcsA possesses an electric dipole moment of magnitude 403 Debye while ClC has a macrodipole whose magnitude is about five times larger, 1983 Debye, thereby contributing to differentiate their membrane electric barriers. The dipole vectors of both proteins are aligned along the corresponding selectivity filters. This result suggests that potassium and chloride ion channels are not passive with respect to the movement of ions across the membrane and the ionic motion might be partially driven by the electric field of the protein in conjunction with the electrochemical potential of the membrane.