Context of the sodium cluster in relation to the central pore. A. Backbone representation of the trimer showing the global position of the cluster. Each monomer is coloured separately and the sodium ions within the cluster are shown as red spheres. B. The local environment of the cluster, demonstrating the proximity of the coordinating aspartates (Asp146, Asp150 and Asp198) to the three lysine residues within the channel (Lys143, Lys201 and Lys205). Lys201 is involved in charge neutralisation within the cluster. Sodium ions are shown as red spheres.