Unveiling the Possible Oryzalin-Binding Site in the α-Tubulin of Toxoplasma gondii

Dinitroaniline derivatives have been widely used as herbicidal agents to control weeds and grass. Previous studies demonstrated that these compounds also exhibit good antiparasitic activity against some protozoan parasites. Oryzalin (ORY), a representative dinitroaniline derivative, exerts its antiprotozoal activity against Toxoplasma gondii by inhibiting the microtubule polymerization process. Moreover, the identification of ORY-resistant T. gondii lines obtained by chemical mutagenesis confirmed that this compound binds selectively to α-tubulin. Based on experimental information reported so far and a multiple sequence analysis carried out in this work, we propose that the pironetin (PIR) site is the potential ORY-binding site. Therefore, we employed state-of-the-art computational approaches to characterize the interaction profile of ORY at the proposed site in the α-tubulin of T. gondii. An exhaustive search for other possible binding sites was performed using the Wrap "N" Shake method, which showed that ORY exhibits highest stability and affinity for the PIR site. Moreover, our molecular dynamics simulations revealed that the dipropylamine substituent of ORY interacts with a hydrophobic pocket, while the sulfonamide group formed hydrogen bonds with water molecules at the site entrance. Overall, our results suggest that ORY binds to the PIR site on the α-tubulin of the protozoan parasite T. gondii. This information will be very useful for designing less toxic and more potent antiprotozoal agents.