Study On The Mechanism Of Enoyl-ACP Reductase (FabI) With Triclosan Derivatives And The Antibacterial Mechanism

FabI,enoyl-ACP reductase(ENR),is the rate limiting enzyme in the last step of fatty acids biosynthesis in many bacteria.Triclosan(TCL),one of the inhibitors of FabI,depresses the substrate(trans-2-enoyl-ACP)binding with Fab I to hinder the fatty acid synthesis as a kind of bactericide employed in commodity widely.In this paper,the mechanism of Enoyl-ACP reductase(FabI)with Triclosan derivatives and the antibacterial mechanism have been studied.In this paper,we first used molecular docking and molecular dynamics simulation,DSSP and MM-PBSA to study the interaction between triclosan derivatives with EcFab I-NAD~+ binary complex.It included RMSD,RMSF,hydrogen bond,secondary structure and relative combined with free energy changing with the simulation time.Our study clearly shows that the hydroxyl group of A ring is very significant.It is not only beneficial to form hydrogen bonds with receptor,but also advantageous to induce the conformation of activity pocket residues to stable.The modified group of 4-chlorine of A ring is good for the ligand binding for Fab I.Because that modified group facilitated the formation of hydrogen bonds between FabI and receptor.As well as if does not have this modified group,the van der Waals energy and electrostatic energy will decrease sharply.The 5'-methyl of B ring make the polar solvation energy increase and make the hydroxychlorophene ring deviate from NAD~+,which is not conducive to the binding with receptor.The 4'-methoxy group of B ring could not form hydrogen bond with the amino of A95 and enhance the van der Waals energy,but also make the conformation of activity pocket residues unstable.Second,we used molecular dynamics simulation to study the changing rule of the residues conformation and the secondary structure of amino acid residues of Loop area around the active pocket with the simulation time.It revealed the mechanism of action of TCL with SaFab I.The impact of stability of all complexex,the volatility of each amino acid residues and the comformation of the active site loop of SaFab I,saFab I-NADP+ binary system and saFab I-NADP+-TCL ternary complex with simulation time were studied by molecular dynamics simulation.The study showed that the NADP+ and the inhibitor three could promote the stability of conformation of the protein in different degrees.The NADP+ could promote the stability of conformation of the active site loop Tyr147-Tyr157.And the NADP+ and TCL could promote the stability of the substrate-binding loop Ile94-Phe108 and loop2 Arg194-Phe204 and the active site loop Tyr147-Tyr157.Finally,we used the secondary structure sequence comparison and molecular dynamics simulation to sudy the reason that lead the different biological activity between EcFabI-NAD~+-TCL and EcFab I-NADP+-TCL.SaFabI has one more substrate-binding loop than EcFabI.This substrate-binding loop is flexible,which could work with the the classical substrate-binding loop to close the residue conformation around the active pocket to help the binding about TCL and Fab I.Meanwhile,there is difference between the bindings with coenzyme.In EcFabI,bulky substituents at position 44,appear to shrink the adenine ribose-binding pocket,thus decreasing the affinity towards NADPH.