β-Sitosterol could serve as a dual inhibitor of Trypanosoma congolense sialidase and phospholipase A: in vitro kinetic analyses and molecular dynamic simulations.

The involvement of Trypanosoma congolense sialidase alongside phospholipase A has been widely accepted as the major contributing factor to anemia during African animal trypanosomiasis. The enzymes aid the parasite in scavenging sialic acid and fatty acids necessary for survival in the infected host, but there are no specific drug candidates against the two enzymes. This study investigated the inhibitory effects of β-sitosterol on the partially purified T. congolense sialidase and phospholipase A. Purification of the enzymes using DEAE cellulose column led to fractions with highest specific activities of 8016.41 and 39.26 µmol/min/mg for sialidase and phospholipase A, respectively. Inhibition kinetics studies showed that β-sitosterol is non-competitive and an uncompetitive inhibitor of sialidase and phospholipase A with inhibition binding constants of 0.368 and 0.549 µM, respectively. Molecular docking of the compound revealed binding energies of - 8.0 and - 8.6 kcal/mol against the sialidase and phospholipase A, respectively. Furthermore, 100 ns molecular dynamics simulation using GROMACS revealed stable interaction of β-sitosterol with both enzymes. Hydrogen bond interactions between the ligand and Glu284 and Leu102 residues of the sialidase and phospholipase A, respectively, were found to be the major stabilizing forces. In conclusion, β-sitosterol could serve as a dual inhibitor of T. congolense sialidase and phospholipase A hence, the compound could be exploited further in the search for newer trypanocides.