Time-resolved X-ray solution studies of pH induced conformational changes in a proton-sensitive potassium channel.

We aim to observe structural perturbations using time-resolved X-ray solution scattering (TR-XSS) for the pH sensitive ion channel KcsA. A proof-of-principle study at ID02 of the ESRF used a small amount of beamtime to induce a structural change in KcsA when UV light was used to release caged protons, thereby jumping the sample from pH 7 (neutral) to 4 (acidic). Since those data reveal the end-points of a pH induced transition from one conformation to another, we intend to repeat this study at ID09 where we can incorporate the extra-dimension of time, with the goal of sampling time-delays from a few microseconds to hundreds of milliseconds. As such all the major technical hurdles of this experiment have been validated, and there is every reason to feel confident that a genuinely time-resolved diffraction study should shed new structural insight into the transition from a close to an open conformation of a highly studied potassium channel.