Ion-dependent structure, dynamics, and allosteric coupling in a non-selective cation channel
Adam Lewis, Vilius Kurauskas, Marco Tonelli, Katherine A. Henzler‐Wildman
Abstract
Abstract The selectivity filter (SF) determines which ions are efficiently conducted through ion channel pores. NaK is a non-selective cation channel that conducts Na + and K + with equal efficiency. Crystal structures of NaK suggested a rigid SF structure, but later solid-state NMR and MD simulations questioned this interpretation. Here, we use solution NMR to characterize how bound Na + vs. K + affects NaK SF structure and dynamics. We find that the extracellular end of the SF is flexible on the ps-ns timescale regardless of bound ion. On a slower timescale, we observe a structural change between the Na + and K + -bound states, accompanied by increased structural heterogeneity in Na + . We also show direct evidence that the SF structure is communicated to the pore via I88 on the M2 helix. These results support a dynamic SF with multiple conformations involved in non-selective conduction. Our data also demonstrate allosteric coupling between the SF and pore-lining helices in a non-selective cation channel that is analogous to the allosteric coupling previously demonstrated for K + -selective channels, supporting the generality of this model.