Unbinding Mechanism Of Acetyl-CoA Carboxylase Inhibitors And Interaction Mechanism Of Oxathiapiprolin As A Novel Oxysterol Binding Protein Inhibitor

Acetyl-CoA carboxylase(ACCase)is one of the important herbicide targets.Currently targeted ACCase has successfully developed three types of herbicides:Aryloxyphenoxypropionates(APPs),Cyclohexanediones(CHDs)and Phenylpyrazoline(DEN).According to data from the Pesticide Resistance Committee,ACCase is particularly resistant to APPs and CHDs,so the task of developing new inhibitors is imminent.Here,computational studies on APP(diclofop)and CHD(tepraloxydim)were carried out to investigate their unbinding mechanism by means of steered molecular dynamics(SMD),providing theoretical basis for the design of new inhibitors.The results showed that the binding sites of diclofop and tepraloxydim in ACCase were not exactly the same,and there were obvious differences in their unbinding pathways.The PMF of diclofop(?70 kcal/mol)is higher than that of tepraloxydim(?22 kcal/mol).The rank of PMF is fairly well correlated with that of the inhibition activities(diclofop IC50=0.1?mol/L and tepraloxydim IC50=1.6?mol/L),confirming the correctness of our method.For the dissociation of diclofop,1)The H-bonds formed between the carboxyl oxygen atom of diclofop and Ala1627,Ile1735 are not only important for the stable binding of diclofop,but also to prevent it unbinding from the binding site;2)The methyl group of diclofop formed hydrophobic interactions with Leu 1705 and Leu2025' during the dissociation of the ligand,hindering the dissociation of the ligand-Therefore,we propose to transform this group into other hydrophobic groups,but the group should not be too large,otherwise it will cause steric hindrance to hinder ligand binding;3)Thr1757 formed a H-bond with diclofop during its dissociation and hindered its unbinding process.For the dissociation of tepraloxydim,1)The H-bonds between tepraloxydim and Ala1627,Ile1735 were essential for ligand binding and preventing its dissociation;2)The ethyl group of tepraloxydim was associated with Ile 1629,Leu2024',Leu2025' and Ile2033'forming hydrophobic interactions to block the unbinding of the ligand.For molecular design,we recommend to modify this part with other hydrophobic groups;3)Gly1758 and Thr1757 formed transient H-bonds with tepraloxydim during the dissociation of tepraloxydim,which delayed the unbinding process.The success of oxathiapiprolin as the first oxysterol binding protein(OSBP)inhibitor for oomycetes control is regarded as an important milestone in the history of fungicide discovery.However,its detailed interaction mechanism towards OSBP is still unclear.Meanwhile,some plant pathogenic oomycetes have developed medium to high resistance to oxathiapiprolin.Therefore,it is of great significance to study the binding mode of oxathiapiprolin to OSBP for drug design.Herein,the 3D structure of P.capsici OSBP was built and the interaction mechanism of oxathiapiprolin was investigated systematically by integrating molecular docking,molecular dynamics simulations,and MM/PBSA calculations.The results showed that oxathiapiprolin bound with pcOSBP forming H-bonds with Leu73,Lys74,Ser69,and water molecules.Subsequently,based on this mode of action,a highly active compound 1e was obtained through substituent optimization.This compound has a good inhibitory effect on wild-type and mutant P.capsici.The most important thing is that the resistance ratio of 1e to mutant strain(G140W)is less than 1.Molecular simulation results showed that the compound 1e formed H-bond with Gln72 when combined with mutant pcOSBP,its butenyl fragment formed hydrophobic interaction with Trp140.The energy contribution of key residues such as Ser69,Gln72,Leu73,Lys74,Leu 164,Arg 174 and Val176 increased,resulting in the binding energy of 1e to mutant pcOSBP(-30.96 kcal/mol)was similar to that of wild-type pcOSBP(-30.57 kcal/mol).The result could be used as a new starting point for further discovery of new OSBP inhibitors.