Fragments 1 and 2 differ in the nature of the allosteric effect in Hsp90.

Abstract

<p><b>(A)</b> The absolute difference in numbers of deuterons (inferred from difference in mass in Daltons (Da) (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 the apo-Hsp90. Regions showing significant differences above a threshold of 0.5 Da (red dashed line) are compared with orthosteric sites (blue boxes) to establish allosteric regions (red boxed). Fragment <b>2</b> does not show any changes in region A4, similar to 17-AAG, while fragment <b>1</b> shows differences, similar to Radicicol. In addition, fragment <b>1</b> shows an allosteric response at the regions A5 (residues 201–213 shown in orange box), which is not observed in the other three ligands. Time points are colored according to key. <b>(B,C)</b> The identified orthosteric (blue) and allosteric regions (red) for fragments are mapped on to the structure of Hsp90 in blue. <b>(C)</b> The allosteric site A5 in Hsp90, which is observed only fragment <b>2</b> is highlighted in orange. Radicicol bound at the ligand binding pocket is shown as sticks (PDB ID: 4EGK).</p