Single-molecular measurements of twisting motions during gating in KcsA potassium channels

Abstract

Crystal structures of potassium channels in open and closed conformations have provided static pictures for the different gating status. To examine dynamic pictures of the channels in function, we recorded gating motions of single KcsA potassium channels with the diffracted X-ray tracking method. The KcsA channels were fixed on a glass plate at the extracellular side, and labelled with a gold nanocrystal at the other side. Irradiations of synchrotron white X-rays elicited diffraction spots from the attached nanocrystal. The motions of the spots, which were recorded at video rate, could be translated into the channel motions in real space. Under gating condition twisting motions around the longitudinal axis with several tens of degrees were observed. These twisting motions were detected from the channels labeled at the end of the cytoplasmic domain or at the end of M2 helices. In either case the observed motions were stopped by an open channel blocker. From these results we concluded that the KcsA channels exhibited global twisting motions during gating, which were originated from the transmembrane domain and transferred to the cytoplasmic domain. [J Physiol Sci. 2008;58 Suppl:S77]