DIRECT PHYSICAL MEASURE OF CONFORMATIONAL REARRANGEMENT UNDERLYING POTASSIUM CHANNEL GATING

In response to membrane depolarization, voltage-gated ion channels und ergo a structural rearrangement that moves charges or dipoles in the m embrane electric field and opens the channel-conducting pathway. By co mbination of site-specific fluorescent labeling of the Shaker potassiu m channel protein with voltage clamping, this gating conformational ch ange was measured in real time. During channel activation, a stretch o f at least seven amino acids of the putative transmembrane segment S4 moved from a buried position into the extracellular environment. This movement correlated with the displacement of the gating charge, provid ing physical evidence in support of the hypothesis that S4 is the volt age sensor of voltage-gated ion channels.