  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.
