Study On The Metabolic Activation And Degradation Mechanism Of Typical Endocrine Disrupting Chemicals Under The Action Of Enzymes

Endocrine disrupting chemicals(EDCs)can enter the environment through a variety of pathways and have potential toxic effects on organisms.The concentration of EDCs will increase with the gradation of the food chain,it will be difficult to decompose and excrete after entering the animal body.Therefore,the biological enrichment of the food chain will expose humans to higher concentrations of EDCs,exacerbating health risks.Using biological enzymes to catalyze degradation and metabolic activation to convert EDCs is an efficient method.Considering the limitations of experimental methods,computational simulation is used to predict the metabolic activation and degradation pathways of endocrine disrupting chemicals under the action of biological enzymes.It makes up for the lack of experimental methods to describe the details of the reaction.In this paper,the typical natural estrogen zearalenone and the typical synthetic endocrine disrupting chemical polychlorinated dibenzo-p-dioxin were selected.And molecular dynamics(MD)simulations,quantum mechanics/molecular mechanics(QM/MM)and density functional theory(DFT)methods were used to study the degradation mechanism of zearalenone by zearalenone hydrolase and the metabolic activation mechanism of polychlorodibenzo-p-dioxin(PCDDs)under the action of CYP1A1.The role of important amino acids in the reaction was also explored.The detailed research contents are as follows:(1)By using MD and QM/MM method,we investigated the degradation and detoxification process of zearalenone,a typical natural fungal estrogen,under the action of zearalenone hydrolase RmZHD isolated from Rhinocladiella mackenziei.The results show that the degradation process includes two concerted reaction pathways,the active site contains a catalytic triad Ser-His-Glu as a proton donor.The hydroxylation product is formed by proton transfer and nucleophilic substitution to open the ring.And then the carboxyl group is removed to prevent the female receptor from combining with the resulting product,ZEN toxicity is reduced.Analysis of non-covalent interaction illustrated the hydrogen bonding between key amino acids and ZEN.The electrostatic effects analysis of 16 amino acids outside the QM region proposes residues Asp34 and His 128 are used as the possible mutation target for future mutation design of enzyme RmZHD.(2)We used molecular docking,MD,QM/MM and DFT methods to study the metabolic transformation pathways of typical synthetic EDC,pentachlorodibenzo-p-dioxin(PeCDD)under the catalytic action of cytochrome P450 enzymes.The formation of hydroxylated products comes from two reaction mechanisms,hydrogen atom transfer(HAT)or ? electrophilic addition reaction.In the HAT mechanism,the reaction starts with the extraction of hydrogen atoms of the substrate by Cpd I,and is a reaction mechanism in which a low spin state and a high spin state coexist.In the mechanism of? electrophilic addition reaction,the process of Cpd I attacking the C atom of PeCDD as an oxidant is the rate-determining step of the whole reaction.After the formation of intermediates,hydroxylated products can be generated through the NIH rearrangement reaction,or through the ring-opening reaction of an epoxidation intermediate.NIH rearrangement or epoxidation reaction can only generate metabolic active intermediates,and cannot directly generate hydroxylated PeCDD.The analysis of the mechanism of PCDDs metabolism by cytochrome P450 enzymes has been enriched by analysis of orbital occupancy,electrostatic potential on the molecular surface,non-covalent interaction,and distortion-interaction energy model.