Aim
Staphylococcus aureus is one of the most dreaded pathogens which is acquiring resistance towards the available drugs and we know the antibiotic resistance has become an alarming situation worldwide. The bacteria are also evolving and the ability of bacteria to circumvent the immune system of host is also a way to get it survived inside the host. The killing of pathogen is getting difficult day by day due to their mechanisms to bypass the immune system of host as well. One of the mechanism of microbes are known as anti-oxidative system which enables them to neutralize the oxidative stress generated by host immune response. The system is an enzyme cascade consists of thiol peroxidases, thioredoxin, thioredoxin reductase and NADPH as ultimate electron donor. In the anti-oxidative mechanism Thioredoxin reductase (SaTR) plays a central role and protects the microbe from oxygen and disulfide stress in order to thrive.
Methods
In the presented work we have searched for small molecule inhibitors with pharmacophore-based drug designing approach. An analysis has been conducted on the precise enzyme kinetics of the inhibition of the SaTR enzyme, as well as the likely mechanistic aspects of the inhibition of SaTR by DDHF derivatives using in-silico methods. Not only this, the DDHF capped silver nanoparticle has also been synthesized and characterized for the better bioavailability and bactericidal activity of lead compounds.
Result and Discussion
The in-silico and in-vitro tests demonstrate that DDHF is a competitive inhibitor of SaTR. The binding of DDHF to the NADPH site inhibits the reduction cycle and thus impairs the catalytic activity of the enzyme. Moreover, a thorough examination of the enzyme kinetics of the most effective DDHF derivative inhibitor, DDHF20 (with a dissociation constant of around 69µM), revealed its capacity to effectively compete with the redox-active labile cofactor NADPH of SaTR. As a result, it may disrupt the electron transfer interaction between NADPH and FAD. The in-vitro bactericidal activity confirms DDHF potential to kill microbe under oxidative stress. The synthesized DDHF capped silver nanoparticles have been examined and shown to be non-cytotoxic and stable molecules in biological fluids. The findings of in-silico docking and all atomistic molecular dynamics (MD) simulations indicate a robust and enduring binding of DDHF20 to the highly conserved NADPH binding pocket of SaTR. The in-silico investigations provide a comprehensive explanation of the inhibitory mechanism as well. By specifically targeting this protein with a lead molecule that is resistant to resistance, we can activate the host immune system to eliminate the bacterium by inducing oxidative stress.