Abstract
For the cytoplasmic domain (CD) of potassium channels, crucial roles for mediating intracellular stimuli and assembling subunits have been investigated. KcsA channel, with only 160 amino acid residues, possesses intracellular stretches in the C-terminus, which forms CD in the tetrameric channel. KcsA channels are activated by intracellular acidic pH, the mechanism of pH-sensing remains unsolved. Also only predicted structure is available for the CD. Present study investigated surface structure of the CD in KcsA channel by developing a novel approach. Single cystein was introduced into various parts of the channel and specific reaction between introduced cystein and a flat gold surface was evaluated by surface plasmon resonance signals. All mutations did not alter single-channel properties, such as single-channel current-voltage curves and the gating characteristics. In contrast to the closed channel at pH 7.5, various sites in the CD became exposed to the surface when channels were activated (pHi = 4.0). These observations indicate that the cytoplasmic domain takes several conformational states when the channel is actively gating. We have also investigated the effect of open channel blocker, tetrabutylammonium, on the conformational changes in the CD. [J Physiol Sci. 2006;56 Suppl:S157]
