Functional heterogeneity of arrhythmogenic KCNQ1 S1 mutants reveals dependence on the number of KCNE1 subunits in the IKs channel complex.

Background

A cluster of closely spaced residues located at the extracellular end of the S1 transmembrane domain in KCNQ1 (Q1, residues 140-147) harbors six mutations associated with both gain- and loss-of-function (GoF and LoF) arrhythmic diseases. Whether severity of the mutation phenotype is affected by the stoichiometric ratio of KCNE1 (E1) to Q1 is unknown.

Objective

This study aims to determine how the six mutations differentially alter the gating properties of Q1 alone and of IKs at different fixed E1:Q1 stoichiometries.

Methods

Concatemers were used to generate known stoichiometries of E1:Q1 (Q1 alone; E1QQ, fixed 2:4; and E1Q, fixed 4:4), while incorporating S1 mutations into Q1. Whole-cell voltage clamp protocols were applied to channels expressed in mammalian tsA201 cells and computational modeling was used to provide a physiological perspective.

Results

Q1 S1 mutants had wide-ranging effects on channel gating despite their proximity to one another, and these phenotypes were modulated by the E1:Q1 stoichiometry. Increasing the number of E1 in the channel complex generally exaggerated mutant phenotypes. Atrial and ventricular action potential clamp experiments and computational modeling generally supported the phenotype of mutation-associated diseases in more physiological systems, except for the long-QT-associated T144A and atrial-fibrillation-associated Q147R.

Conclusion

The functional impact of S1 mutants in Q1 varies depending on the number of associated E1, suggesting that E1:Q1 stoichiometry may represent a previously underappreciated regulator of Q1 variant phenotype.