Exploring the inhibition mechanisms of momordin Ic on S. aureus serine/threonine phosphatase (Stp1) using theoretical and experimental approaches

Serine/threonine phosphatase (Stp1) modulates the expression of Staphylococcus aureus (S. aureus) by regulating cysteine phosphorylation. Therefore, Stp1 is a promising target for inhibiting S. aureus infection. In this study, the natural compound momordin Ic was found to have significant inhibitory activity against Stp1 through virtual screening and phosphatase assays. Molecular dynamics simulations and enzyme kinetics experiment demonstrated that momordin Ic binds to the active center of Stp1, thereby reducing its affinity for the substrate. Radius of gyration, solvent-accessible surface area, and root mean square fluctuation analyses showed that drug-bound Stp1 was more stable than free protein. Moreover, Gly41, His42, Lys43, Thr102, Asn162, and Ile164 played crucial roles in the binding of Stp1 to momordin Ic. The binding sites were analyzed using phosphatase and fluorescence quenching experiments. This study demonstrates that momordin Ic is an effective Stp1 inhibitor and provides a foundation for the development of highly effective antitoxic drugs.