The structural basis of the divalent cation blocking on tetrameric cation channel

Abstract Divalent cation blocking is observed in various tetrameric ion channels. For the blocking, a divalent cation is thought to stack in the ion pathway of the channel, but this has not yet been directly observed, so the blocking mechanism by these small divalent cations remains uncertain. Here, we elucidated the divalent cation blocking mechanism by reproducing the blocking effect into NavAb, a well-studied tetrameric sodium channel. Our crystal structures of NavAb mutants showed that the mutations increasing the hydrophilicity of the inner vestibule of the pore domain enable a divalent cation to stack on the ion pathway. Furthermore, molecular dynamics simulation showed that the stacking calcium ion repels the sodium ions at the bottom of the selectivity filter. These results suggest the primary mechanism of the divalent cation block in biologically essential channels.