Iso-mukaadial acetate and ursolic acid acetate inhibit the chaperone activity of Plasmodium falciparum heat shock protein 70-1.

Plasmodium falciparum is the most lethal malaria parasite. The present study investigates the interaction capabilities of select plant derivatives, iso-mukaadial acetate (IMA) and ursolic acid acetate (UAA), against P. falciparum Hsp70-1 (PfHsp70-1) using in vitro approaches. PfHsp70-1 facilitates protein folding in the parasite and is deemed a prospective antimalarial drug target. Recombinant PfHsp70-1 protein was expressed in E. coli BL21 cells and homogeneously purified by affinity chromatography. The interaction between the compounds and PfHsp70-1 was evaluated using malate dehydrogenase (MDH), and luciferase aggregation assay, ATPase activity assay, and Fourier transform infrared (FTIR). PfHsp70-1 prevented the heat-induced aggregation of MDH and luciferase. However, the PfHsp70-1 chaperone role was inhibited by IMA or UAA, leading to both MDH and luciferase's thermal aggregation. The basal ATPase activity of PfHsp70-1 (0.121 nmol/min/mg) was closer to UAA (0.131 nmol/min/mg) (p = 0.0675) at 5 mM compound concentration, suggesting that UAA has no effect on PfHsp70-1 ATPase activity. However, ATPase activity inhibition was similar between IMA (0.068 nmol/min/mg) (p < 0.0001) and polymyxin B (0.083 nmol/min/mg) (p < 0.0001). The lesser the Pi values, the lesser ATP hydrolysis observed due to compound binding to the ATPase domain. FTIR spectra analysis of IMA and UAA resulted in PfHsp70-1 structural alteration for β-sheets shifting the amide I band from 1637 cm-1 to 1639 cm-1, and for α-helix from 1650 cm-1 to 1652 cm-1, therefore depicting secondary structural changes with an increase in secondary structure percentage suggesting that these compounds interact with PfHsp70-1.