A specialized molecular motion opens the Hv1 voltage-gated proton channel

The Hv1 proton channel is unique among voltage-gated channels for containing the pore and gate within its voltage-sensing domain (VSD). Opening of the pore has been proposed to include assembly of the selectivity filter between the third arginine (R3) of S4 and an aspartate of S1 (D1). We asked whether gating involves a motion of S1 using Ciona intestinalis Hv1. We find that channel opening is concomitant with solution access from the cytoplasm deep into the pore-lining face of S1. Voltage- and patch-clamp fluorometry show that this involves a motion of S1 relative to its surround. S1 motion, and the S4 motion that precedes it, are each influenced by residues on the other helix, suggesting a dynamic interaction between S1 and S4. Our findings suggest that the S1 of Hv1 has specialized to function as part of the channel's gate.