Fig. 3: Voltage sensor domain arrangement and pore properties of Kv3.1a.

a Cartoon representation of the VSD S1–S4 (S3 is omitted for clarity) in Kv31a, showing the relative positioning of the gating charges R1–R4 (blue labelled) in S4 (shown in yellow) with respect to conserved residues (F256 and E249) of the hydrophobic charge transfer centre (CTC), located in S2 (shown in light green). Blue circles highlight voltage-sensing gating residues located above the position of conserved F256 of the CTC, which is represented by the dotted red line. b Cartoon representation of the VSD arrangement in Kv1.2-2.1 (pdb 6EBK), highlighting that all four voltage-sensing charges R1–R4 (blue circles) are located above F233 compared to only three (R1–R3) in Kv3.1a shown in panel (a). c Plot of the Kv3.1a pore radius, as determined by MOLE⁷⁷. Red dotted line marks the radius of hydrated K⁺. d Sequence of S4 residues for Kv3.1a (top) and Kv1.2-2.1 (bottom) with the main voltage-sensing R/Q residues within the conserved arginine-rich motif highlighted in blue. Blue boxes encircle voltage-sensing arginines which are located above the CTC. e Cross-membrane view of the Kv3.1a pore domain and selectivity filter. For clarity, only two chains are shown. The pore diameter is shown as light grey surface representation. Residues in the PVP motif are shown as green sticks, major pore lining residues are highlighted by black frames. Conserved aromatic residues in the lower S6T gate are shown as sticks. F345 in S5 (unique to Kv3 family) is shown as black stick representation. Dashed line indicates cα distance between V425 (framed in red), a residue relevant for the gain-of-function mutation V425M associated with epileptic encephalopathy¹⁵. f Cytoplasmic view of the open pore with pore-lining S6 helices from all four subunits shown as cartoon representation. Dashed line indicates cα distance between P433 from two diagonal subunits.