Abstract
Recent structural information on the Kv 1.2 potassium channel revealed two interaction surfaces between the voltage sensor and pore domains. While the lower interaction surface is intra-subunit and its contribution to the electro-mechanical coupling underlying channel opening is relatively understood, the upper (domain-swapped) interaction surface is inter-subunit and its contribution to the mechanism of Kv channel gating is not yet clear. Evolutionary information, mutagenesis and covalent cross linking analyses indicated that residues spanning the upper interface play an important role in Kv channel function. These analyses, however, did not provide mechanistic information regarding possible rearrangements associated with this interface during Kv channel gating. To further address the nature of the upper interaction surface, whether dynamic or static, we assessed the contribution of such inter-subunit domain swapping interactions to Kv channel gating by combining electrophysiology recordings of wild type and (upper interface) mutant proteins, introduced in the context of a tandem-dimer channel construct, with thermodynamic coupling analysis by means of double-mutant cycles formalism. Our results reveal that: (1) point mutations of pore and voltage-sensor residues at the upper interaction surface stabilize the closed channel state, (2) that pore-voltage sensor residue pairs across the upper inter-subunit interaction surface are coupled and (3) that the coupling is state-dependent and is stronger in the open channel state as compared to the closed state. Overall, our results suggest that the upper interaction surface is dynamic in nature and further support the assertion that the structure of the Kv channel solved is indeed that of the open channel state.
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