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

We will use time-resolved X-ray solution scattering (TR-XSS) to study the pH sensitive ion channel KcsA. An earlier experiment at ID09 (LS-3224) was very successful, with changes in the X-ray scattering observe when UV light was used to release caged protons, thereby jumping the sample from pH 7 (neutral) to pH 4 (acidic). We will build from this earlier experiment to test if point-mutations that inactivate the enzyme also suppress the observed conformational changes. Since the release of photocaged protons is very fast, we will also collect data for early-microsecond delays, aiming to measure the rise of the pH induced conformational change in KcsA. Finally, we will reproduce the pH induced conformational change in KcsA using a mixing flow-cell, with the goal of developing a generic approach to TR-XSS. Our studies of KcsA mutants will provide new structural insight into the transition from a closed to an open conformation of this highly studied potassium channel.