Question: 

K⁺ channels are promising drug targets. Despite major efforts only a few specific blockers have been found. Channel blockers bind within the inner cavity to the selectivity filter and residues of the S6 segments. This recurring theme is highly conserved and the reason why most synthetic blockers cannot distinguish between different types of K⁺ channels. For Kv channels this is even more pronounced as they have highly conserved S6 segments and thus the drug binding site for all Kv channels is almost identical. Psora-4 however is a non-toxin blocker that can discriminate between Kv families. We aimed to identify the underlying mechanism of this unusual and surprising Kv1-specificity.

Methods: 

Systematic alanine-scanning mutagenesis and molecular modelling were used to identify the Psora-4 binding site in Kv1 channels.

Results: 

Psora-4 binds to the central cavity of Kv1.5 channels and in addition, and in contrast to other channel blockers, to side pockets located between the pore domain and voltage sensor of adjacent subunits. Summarizing, we identified the four side pockets present in all voltage gated channels as a novel drug binding site.

Conclusion: 

We propose that drug binding to the side pockets allosterically modulates block within the central cavity. This novel binding site provides a molecular basis to develop selective Kv channel blockers and reveals a novel blocking mechanism for voltage-gated channels.