Single-molecule structure-function analysis of the pH-dependent gating of the KcsA potassium channel

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The pH-dependent gating of the KcsA potassium channel was examined by enhancing the spacial and temporal resolutions of the diffracted X-ray tracking method. Unlike previous steady-state measurements, the solution pH was jumped by using the caged compound, and transient behavior of the gating conformational change was recorded with the high-speed image sampling (5000 frame/sec). We found that the clockwise twisting was initiated upon acidic pH change. By using the atomic force microscopy (AFM), we revealed the substantial shortening of the longitudinal length of the KcsA channel in the membrane embedded condition. These results indicate that channel shows a spring-like motion, involving simultaneous twisting and shortening, upon opening of the channel.