The trajectory of discrete gating charges in a voltage-gated potassium channel

Positively-charged amino acids respond to membrane potential changes to drive voltage sensor movement in voltage-gated ion channels, but determining the trajectory of voltage sensor gating charges has proven difficult. We optically tracked the movement of the two most extracellular charged residues (R1, R2) in the Shaker potassium channel voltage sensor using a fluorescent positively-charged bimane derivative (qBBr) that is strongly quenched by tryptophan. By individually mutating residues to tryptophan within the putative trajectory of gating charges, we observed that the charge pathway during activation is a rotation and a tilted translation that differs between R1 and R2 and is distinct from their deactivation pathway. Tryptophan-induced quenching of qBBr also indicates that a crucial residue of the hydrophobic plug is linked to the Cole-Moore shift through its interaction with R1. Finally, we show that this approach extends to additional voltage-sensing membrane proteins using the Ciona intestinalis voltage sensitive phosphatase (CiVSP).