Fig. 1. Exemplary illustration of important ion channel features using a K_Ca3.1 channel cryo-EM structure (pdb 6cnn [3]). a) A tetrameric ion channel (each subunit is coloured differently). b) Overview about the important feature of one subunit: Helix S5/S6 form the ion channel pore surrounded by membrane-embedded helices S1-S4. Helices HA/HB build the binding site for calmodulin which is important for activation. The channel gate regulates ion conductance, and the selectivity filter is responsible for ion specificity. c) Surface representation with clipped surface showing the inner channel pore.