Kv1.3 is a homotetrameric voltage-activated potassium (Kv) channel within the Shaker family that was initially identified in T lymphocytes, where it plays a critical role in T cell activation. Inhibitors of Kv1.3 impair T cell activation and thus are promising leads as immunosuppressives to treat autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis, and type 1 diabetes. Upon sustained activation, Kv1.3 undergoes C-type inactivation, a process that results from dilation of the ion selectivity filter and diminished K + ion permeation. Numerous small-molecule inhibitors of Kv1.3 have been developed, but achieving selectivity over other Kv1 family members remains a major challenge. 5-(4-phenoxybutoxy) psoralen (PAP-1) is a state-dependent inhibitor that preferentially binds Kv1.3 in its C-type inactivated state. PAP-1 exhibits 23-fold selectivity over Kv1.5 and 33- to 125-fold selectivity over other Kv1-family channels, with pronounced activity at low nM concentrations. To elucidate the mechanism of PAP-1 inhibition of Kv1.3, we determined cryo-EM structures of wild-type Kv1.3 in the C-type inactivated state bound to PAP-1 at 3.5 Å overall resolution, as well as the Kv1.3 G427H mutant in the conducting state bound to PAP-1, at 3.4 Å overall resolution. Our structures reveal that PAP-1 binds underneath the selectivity filter and contacts several residues with the pore-lining S6 helix and slightly distorting the channel’s 4-fold symmetry. We are currently refining these structures, solving structures of PAP-1 bound to Kv1.3 under different conditions and studying the inhibitory mechanism using electrophysiology to provide mechanistic insight into PAP-1 recognition and the design of more selective Kv1.3-targeted therapeutics.
Selvakumar et al. (Sun,) studied this question.