Fig. 4: A summary of ion coherence-determined transport through the KcsA channel.

Initially, the confined K⁺ ions (K1, K2, K3) in the filter coherently oscillate together, with the help of ion-ion coupling caused by the negatively charged O atoms of C-O bonds on the wall of the filter. Meanwhile, one K⁺ ion (K4) performs free motion in the cavity. Top: Three steps of coherent ion transport. Step I: The K4 ion enters the filter and coherently oscillates with the ions K1, K2 and K3. Step II: The four confined ions in Filter+ coherently oscillate together, during which the ions undergo a coherent ion transfer (labeled Proc + ) as the directional key of transport. P+ indicates the probability of Proc + . Step III: The ion K1 moves out of the Filter+ and becomes incoherent from the coherent ions K2, K3 and K4. Bottom: An alternative process (Proc–) instead of Proc+ in step II, i.e., the ion K4 moves back to the cavity. An increase in the KcsA ion coherence \({\bar{\alpha }}_{{{{\rm{F}}}}}\) can cause a clear decrease in the probability P– of Proc– at a critical value of coherence, i.e., a coherence-induced transition, leading to a large increase in ion flux. The dashed orange and blue lines indicate the maximum probability locations of KcsA-confined ions and the terminus of the KcsA Filter + , respectively.