Structure of the human K 2P 13.1(THIK-1) channel reveals a novel hydrophilic pore restriction and lipid cofactor site.

The halothane-inhibited K _2P leak potassium channel K _2P 13.1 (THIK-1) ^1-3 is found in diverse cells ^1,4 including neurons ^1,5 and microglia ^6-8 where it affects surveillance6, synaptic pruning7, phagocytosis7, and inflammasome-mediated interleukin-1β release ^6,8,9 . As with many K _2P s ^1,5,10-14 and other voltage-gated ion channel (VGIC) superfamily members ^3,15,16 , polyunsaturated fatty acid (PUFA) lipids modulate K _2P 13.1 (THIK-1) ^1,5,14,17 via a poorly understood mechanism. Here, we present cryo-electronmicroscopy (cryo-EM) structures of human K _2P 13.1 (THIK-1) and mutants in lipid nanodiscs and detergent. These reveal that, unlike other K _2P s ^13,18-24 , K _2P 13.1 (THIK-1) has a two-chamber aqueous inner cavity obstructed by a M4 transmembrane helix tyrosine (Tyr273, the flow restrictor). This hydrophilic barrier can be opened by an activatory mutation, S136P ²⁵ , at natural break in the M2 transmembrane helix and by intrinsic channel dynamics. The structures also reveal a buried lipid in the P1/M4 intersubunit interface at a location, the PUFA site, that coincides with the TREK subfamily K _2P modulator pocket for small molecule agonists ^18,26,27 . This overlap, together with the effects of mutation on K _2P 13.1 (THIK-1) PUFA responses, indicates that the PUFA site lipids are K _2P 13.1 (THIK-1) cofactors. Comparison with the PUFA-responsive VGIC Kv7.1 (KCNQ1) ^28-31 reveals a shared role for the equivalent pore domain intersubunit interface in lipid modulation, providing a framework for dissecting the effects of PUFAs on the VGIC superfamily. Our findings reveal the unique architecture underlying K _2P 13.1 (THIK-1) function, highlight the importance of the P1/M4 interface in control of K _2P s by both natural and synthetic agents, and should aid development of THIK subfamily modulators for diseases such as neuroinflammation ^6,32 and autism ⁶ .
Competing Interests: Competing interests The authors declare no competing interests.