Structure of the voltage-gated potassium channel K_V1.3: Insights into the inactivated conformation and binding to therapeutic leads

ABSTRACT

The voltage-gated potassium channel K_V1.3 is an important therapeutic target for the treatment of autoimmune and neuroinflammatory diseases. The recent structures of K_V1.3, Shaker-IR (wild-type and inactivating W434F mutant) and an inactivating mutant of rat K_V1.2-K_V2.1 paddle chimera (K_VChim-W362F+S367T+V377T) reveal that the transition of voltage-gated potassium channels from the open-conducting conformation into the non-conducting inactivated conformation involves the rupture of a key intra-subunit hydrogen bond that tethers the selectivity filter to the pore helix. Breakage of this bond allows the side chains of residues at the external end of the selectivity filter (Tyr447 and Asp449 in K_V1.3) to rotate outwards, dilating the outer pore and disrupting ion permeation. Binding of the peptide dalazatide (ShK-186) and an antibody-ShK fusion to the external vestibule of K_V1.3 narrows and stabilizes the selectivity filter in the open-conducting conformation, although K⁺ efflux is blocked by the peptide occluding the pore through the interaction of ShK-Lys22 with the backbone carbonyl of K_V1.3-Tyr447 in the selectivity filter. Electrophysiological studies on ShK and the closely-related peptide HmK show that ShK blocks K_V1.3 with significantly higher potency, even though molecular dynamics simulations show that ShK is more flexible than HmK. Binding of the anti-K_V1.3 nanobody A0194009G09 to the turret and residues in the external loops of the voltage-sensing domain enhances the dilation of the outer selectivity filter in an exaggerated inactivated conformation. These studies lay the foundation to further define the mechanism of slow inactivation in K_V channels and can help guide the development of future K_V1.3-targeted immuno-therapeutics.

GRAPHICAL ABSTRACT

KEYWORDS:

• Voltage-gated potassium channel
• cryogenic electron microscopy
• peptide toxin
• molecular modeling and docking
• T cells
• autoimmune diseases

Acknowledgments

We thank Ong Seow Theng and Stephanie Shee Min Goay for assistance with Figures 1 and 2. We thank Heike Wulff and Dorothy Wai for critiquing our manuscript. The publication costs for this paper were partially paid by the Washington Foundation for Molecular Pharmacology.

Disclosure statement

KGC is the co-inventor of a patent on dalazatide that has been licensed by the University of California Irvine to TEKv Therapeutics.

Data availability statement

All structures discussed in this review are available in the Protein Data Bank.

Author contributions

George Chandy and Ray Norton drafted and edited the manuscript. Karoline Sanches prepared the figures and figure legends and edited the manuscript.

Additional information

Funding

This work was funded in part by the Australian Research Council Centre for Fragment-Based Design [IC180100021].