Toxoplasma gondii aspartic protease 5 (TgASP5): Understanding structural details and inhibition mechanism.

Toxoplasma gondii, a worldwide prevalent parasite, is responsible for causing toxoplasmosis by infecting almost all warm-blooded animals, including humans. To establish a successful infection, the parasite exports a series of effector proteins which modulates the host immune system; Golgi-resident T. gondii aspartyl protease 5 (TgASP5) plays an essential role in the maturation and export of these effector proteins. This is the first report of the detailed structural investigation of the TgASP5 mature enzyme. Molecular modeling and all-atom simulation provided in-depth knowledge of the active site architecture of TgASP5. The analysis of the binding mode of TEXEL substrate highlighted the importance of the active site residues forming the pocket; the Ser505, Ala776 and Tyr689 in the S2 binding pocket provide the specificity towards Arg at the P2 position. Our study also provides insights into the binding mode of the known inhibitor RRLStatine. Screening the known aspartic protease inhibitors against TgASP5 active site and performing 100 ns all-atom molecular dynamic simulations, MM-PBSA binding energy calculations provided the best nine inhibitor protein complexes. Besides that, Principal Component Analysis (PCA) was employed to identify the change in protein dynamics with respect to the substrate and ligand binding. TgASP5 is essential for the fitness and virulence of the parasite; inhibiting this enzyme can be a possible therapeutic strategy against toxoplasmosis. Our study put forth the inhibitors which can act as initial scaffolds for developing potent mechanistic inhibitors against TgASP5. ### Competing Interest Statement The authors have declared no competing interest.