Predicting Allosteric Effects from Orthosteric Binding in Hsp90-Ligand Interactions: Implications for Fragment-Based Drug Design
Fig 4
(A) Orthosteric regions identified by structural and HDXMS analysis overlap with changes in both ligands and fragments. 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 form of Hsp90. The panels A to D show regions showing differences upon binding Radicicol, 17-AAG, fragments 1 and 2, respectively. Regions showing significant differences above a threshold of 0.5 Da (red dashed line) are correlated with structural data to define orthosteric sites. Peptides spanning these ligand binding sites which make orthosteric interactions with fragments are marked in blue boxes are divided into the same four orthosteric regions O1 to O4, observed in Radicicol and 17-AAG. Fragment 2 shows minimal protection in the region O2 as it is oriented away in this region, consistent with deuterium exchange data.