Effects of inhibitors on Hsp90’s conformational dynamics, cochaperone and client interactions

Abstract

The molecular chaperone and heat-shock protein Hsp90 has become a central target in anti-cancer therapy. Nevertheless, the effect of Hsp90 inhibition is still not understood at the molecular level, preventing a truly rational drug design. Here we report on the effect of the most prominent drug candidates, namely radicicol, geldanamycin, derivatives of purine and novobiocin, on Hsp90s characteristic conformational dynamics and the binding of three interaction partners. Unexpectedly, the global opening and closing transitions are hardly affected by Hsp90 inhibitors. Instead, the conformational equilibrium, as well as the associated kinetic rate constants remain almost untouched. Moreover, we find no significant changes in the binding of the cochaperones Aha1 and p23 nor of the model substrate {Delta}131{Delta}. This holds true for both, competitive and allosteric inhibitors. Therefore, direct inhibition mechanisms, affecting only one molecular interaction, are unlikely. Based on our results, we speculate that the inhibitory action observed in vivo is caused by a combination of subtle effects, which can be used in the search for novel Hsp90 inhibition mechanisms.