Panel A highlighting hydrogen bonds between N1477 and F1304, and P1473 and Q1309. Panel B displays the effects of removing these hydrogen bonds (Q1309A, Q1309L, N1477D) on fast inactivation, showing severely impaired inactivation. Panel C illustrates the coupling between the IFM motif and the pore region through aromatic and hydrophobic interactions, specifically between F1291 and F1304, and I1589 and the IFM motif. Panel D shows the effects of mutations F1291A and I1589A on fast inactivation, indicating severe impairment and complete removal of inactivation when both mutations are present.
Structural components and interactions involved in fast inactivation. (A) Hydrogen bonds couple the DIV VSD and DIII–DIV linker movements. Two hydrogen bonds are identified: N1477 (DIV S4–S5 linker, in orange) with F1304 (IFM motif, in rose), P1473 (DIV S4–S5 linker) with Q1309 (DIII–DIV linker). (B) Removal of the hydrogen bonds (Q1309A, Q1309L, and N1477D) leads to severely impaired fast inactivation. (C) IFM motif and pore region are coupled through aromatic and hydrophobic interaction. F1291 (DIII S6, in green) forms a t-shaped pi–pi VSD interaction with F1304 (IFM motif) and I1589 (DIV S6, in olive) forms a hydrophobic interaction with IFM motif. (D) F1291A and I1589A lead to severe impairment in fast inactivation, and when both are simultaneously mutated, the inactivation is completely removed. Modified from Liu et al. (2025).