Distinguishing orthosteric and allosteric effects in Hsp90.

Abstract

<p><b>(A)</b> The absolute difference in numbers of deuterons (y-axis) between the free and ligand bound state is plotted for each pepsin digest fragment listed from the N to C terminus (x-axis) of Hsp90 for each deuterium exchange time point (t = 0.5, 2, 5, 10 min) in a ‘difference plot’. Shifts in the positive scale represent decreases in deuterium exchange and shifts in the negative scale represent increases in deuterium exchange when compared to apo-Hsp90. Regions showing significant differences above a threshold of 0.5 Da (red dashed line) are compared with orthosteric sites (blue boxes) to predict allosteric regions. Peptides highlighted in red show regions showing differences in distal allosteric regions, not involved in orthosteric binding. Peptides spanning these regions are marked in red boxes and divided into four allosteric regions A1 to A4. Radicicol and 17-AAG shows differences in A1 and A2, while only radicicol showed changes in A3 and A4. Time points are colored according to key. <b>(B)</b> Predicted allosteric regions are mapped on to the structure of Hsp90 (red), together with the orthosteric regions, in blue. Radicicol bound at the ligand binding pocket is shown as sticks (PDB ID: 4EGK).</p