The slowly activating cardiac potassium current (IKs) is generated by a heteromultimeric potassium channel complex consisting of pore-forming (KvLQT1) and accessory (minK) subunits belonging to the KCNQ and KCNE gene families, respectively. Evidence indicating that minK residues line the IKs pore originates from the observation that two minK cysteine mutants (G55C and F54C) render IKs Cd2+-sensitive. We have identified a single cysteine residue in the KvLQT1 S6 segment (Cys-331) that contributes to Cd2+ coordination in conjunction with cysteine residues engineered into the minK transmembrane domain. This observation indicates that minK resides in close proximity to S6 in the IKs channel complex. On the basis of homology modeling that compares the KvLQT1 S6 segment with the structure of the bacterial potassium channel KcsA, we predict that the sulfhydryl side chain of Cys-331 projects away from the central axis of the KvLQT1 pore and suggest that minK resides outside of the permeation pathway. A preliminary model illustrating the orientation of minK with S6 was validated by successful prediction of a novel Cd2+ binding site created within the IKs channel complex by engineering additional cysteine residues into both subunits. Our results indicate the location and orientation of minK within the IKs channel complex and further suggest that Cd2+ exerts its effect on IKs through an allosteric mechanism rather than direct pore blockade.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - Oct 12 2001|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology