Geldanamycin and novobiocin induce unique conformational shifts in Plasmodium falciparum Hsp90

Hsp90 is a molecular chaperone essential for the development of Plasmodium falciparum, the main agent of malaria. The emergence of drug-resistant malaria parasites continues to slow down efforts to control and eliminate the disease effectively. To mitigate antimalarial drug resistance, the World Health Organization (WHO) recommends combination therapies. P. falciparum Hsp90 (PfHsp90) is an essential molecular chaperone. In addition, PfHsp90 is a promising antimalarial drug target, and its inhibition has been shown to reverse resistance to otherwise ineffective antimalarial drugs such as chloroquine. As such, understanding the functional features of PfHsp90 remains important for designing effective antimalarial therapies. In the current study, we expressed and purified recombinant PfHsp90 and investigated its interactions with one of its chaperone partners, PfHsp70, and a co-chaperone, PfHop, which brings the two chaperones into a functional complex to facilitate substrate exchange. Furthermore, we combined in silico and biochemical approaches to compare how PfHsp90 interacts with two known small-molecule inhibitors: geldanamycin and novobiocin. We demonstrated that both geldanamycin and novobiocin bind to PfHsp90 with higher apparent affinity than ATP. Furthermore, novobiocin registered a more dramatic conformational shift on PfHsp90 than geldanamycin. In addition, novobiocin more effectively inhibited the following functions of PfHsp90: self-association, co-chaperone (PfHop) binding, and holdase chaperone activity. We discuss the implications of our findings on the role of PfHsp90 and the prospect of this chaperone as an antimalarial drug target.