Fragment Molecular Orbital Study of the Interaction Between Sarco/Endoplasmic Reticulum Ca-ATPase and Its Inhibitor Thapsigargin Toward Anti-Malarial Development

Plasmodium falciparum, the causative agent of malignant malaria, is insensitive to thapsigargin (TG), a well-known inhibitor of the human sarco/endoplasmic reticulum Ca-ATPase (SERCA). To understand the key factor causing the difference of the sensitivity, the molecular interaction of TG and each SERCA was analyzed by the fragment molecular orbital (FMO) method. While the major component of the interaction energy was the nonpolar interaction, the major difference in the molecular interaction arose from the polar interaction, namely, the hydrogen bonding interaction with a hydroxyl group of TG. Additionally, we successfully confirmed these FMO calculation results by measuring the inhibitory activity of a synthesized TG derivative. Our calculations and experiments indicated that, by replacing the hydroxyl group of TG with another functional group, the sensitivities of TG to human and P. falciparum SERCAs can be reversed. This study provides important information to develop antimalarial compounds targeting P. falciparum SERCA.