Serial Perturbation of MinK in IKs Implies an α-Helical Transmembrane Span Traversing the Channel Corpus

I(Ks) channels contain four pore-forming KCNQ1 subunits and two accessory MinK subunits. MinK influences surface expression, voltage-dependence of gating, conduction, and pharmacology to yield the attributes characteristic of native channels in heart. The structure and location of the MinK transmembrane domain (TMD) remains a matter of scrutiny. As perturbation of gating analysis has correctly inferred the peripheral location and alpha-helical nature of TMDs in pore-forming subunits, the method is applied here to human MinK. Tryptophan and Asparagine substitution at 23 consecutive sites yields perturbation with alpha-helical periodicity (residues 44-56) followed by an alternating impact pattern (residues 56-63). Arginine substitution across the span suggests that as few as eight sites are occluded from aqueous solution (residues 50-57). We favor a TMD model that is alpha-helical with the external portion of the span at a lipid-protein boundary and the inner portion within the channel corpus in complex interactions.