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GYGD pore motifs in neighbouring potassium channel subunits interact to determine ion selectivity

Mark L. Chapman, Howard S. Krovetz and Antonius M. J. VanDongen

1. Cells maintain a negative resting membrane potential through the constitutive activity of background K⁺ channels. A novel multigene family of such K⁺ channels has recently been identified. A unique characteristic of these K⁺ channels is the presence of two homologous, subunit-like domains, each containing a pore-forming region. Sequence co-variations in the GYGD signature motifs of the two pore regions suggested an interaction between neighbouring pore domains.

2. Mutations of the GYGD motif in the rat drk1 (Kv2.1) K⁺ channel showed that the tyrosine (Y) position was important for K⁺ selectivity and single channel conductance, whereas the aspartate (D) position was a critical determinant of open state stability.

3. Tandem constructs engineered to mimic the GYGx-GxGD pattern seen in two-domain K⁺ channels delineated a co-operative intersubunit interaction between the Y and D positions, which determined ion selectivity, conductance and gating.

4. In the bacterial KcsA K⁺ channel crystal structure, the equivalent aspartate residue (D80) does not directly interact with permeating K⁺ ions. However, the data presented here show that the D position is able to fine-tune ion selectivity through a functional interaction with the Y position in the neighbouring subunit.

5. These data indicate a physiological basis for the extensive sequence variation seen in the GYGD motifs of two-domain K⁺ channels. It is suggested that a cell can precisely regulate its resting membrane potential by selectively expressing a complement of two-domain K⁺ channels.

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