Research On The Interaction Mechanism Of Lacca Se And Horseradish Peroxidase With Phenolic Pollutants Based On Molecular Docking

Using of pollutant degradation enzyme to disposal environmental pollution is an effective and green pollution control method and is the hot topic in environmental protection research.Experiments are difficult to analyze the molecular mechanism of the interactions between enzymes and pollutants.Therefore,applying molecular docking technology to study the binding modes and interactions between pollutant degradation enzyme and pollutants is of grea t significance to understand the process of enzymolysis.It is the new method and thinking to solve the environmental problem.Molecular docking technology is a method to predict and optimize the binding mode of receptor and ligand which is originally applied to virtual screening and drug design in medicine.Molecular docking operates fast to obtain reliable results.This method can not only reveal reasonable molecular mechanism in the binding of receptor to the ligand,but also can save scientific research funds and experiment time.This study selected typical pollutants degradation enzymes including Trametes versicolor?T.versicolor?laccase and horseradish peroxidase?HRP?to study the interactions between T.versicolor laccase and nonylphenols?NP?or octylphenols?OP?or chlorophenols?CP?as well as between HRP and CP,respectively.The binding mode,steric interaction,total interaction,binding affinity,hydrogen bonding effect and hydrophobic effect were investigated to study the interaction mechanism of pollution degradation enzyme and pollutants.NP and OP are emerging contaminants.They are typical endocrine disrupting compounds because of their estrogen effects.CP which belong to persistent toxic pollutants,are important halogenated phenolic compounds.NP,OP and CP isomers have different impacts on both of human health and the environment.Therefore,it is of great meaningful to study the interaction mechanism in transformation and removal process of NP,OP and CP isomers.T.versicolor laccase is a fungal enzyme which can effectively degrade phenolic pollutants.Fungal enzyme has advantages on the ability to degrade high concentration of pollutants and low nutritional requirements when compared with bacterial laccase.Experiments have proved that T.versicolor laccase could degrade NP,OP and CP effectively.It proved that the structural characteristics of substrate affect the mechanisms of biodegradation.However,the relevant study of the interactions between T.versicolor laccase and these pollutants at molecular level has not been reported.This study analyzed the interactions between T.versicolor laccase and NP?or OP?,respectively.The results found that strong hydrogen bonding may not exist while hydrophobic effects were necessary.It also indicated that the amino acid residues formed hydrogen bonds including Glu302,Gln242,Ser427,His111,Phe344,Tyr244 and Arg423,while amino acid residues involved in hydrophobic effects including Leu459,Pro346,Ser113,Glu460 and Ala80 in the binding of T.versicolor laccase to NP.In addition,the amino acid residues formed hydrogen bonds including Leu300,Glu460 and Phe344 while the important amino acid residues involved in hydrophobic effects including Leu459,Pro346,Ser113,Leu112 and His111 in the bingding of T.versicolor laccase to OP.Moreover,this study also found that the structure and relative position of alkyl chain in NP and OP affected binding modes,steric interactions,binding affinities,hydrogen bonds and hydrophobic effects.The binding affinities in the complexes of T.versicolor laccase and linear NP or OP isomers were ortho-position>meta-position>para-position.Furthermore,the steric interactions were weaker and binding affinities were stronger in the binding of T.versicolor laccase to branched para-NP isomers?4-NPs?with bulky?-substituent in alkyl chain.Additionally,the steric interactions were weaker in the binding of T.versicolor laccase to 4-?1,1,3,3-tetramethylbutyl?phenol?4t OP?with more complex branched?-substituent in alkyl chain than to 4-?1,1-dimethylhexyl?phenol?4d OP?.Moreover,the amino acid residues formed hydrogen bonds including His111,Ala80,Glu302,Gln242 and Ser427 and the important amino acid residues involved in hydrophobic effect including Phe239,Glu302,Pro79,Phe450,Leu459,Ser113,Tyr244,Gln237,Val426 and Arg423 in the binding of T.versicolor laccase to CP.In addition,the steric interactions and total interactions between T.versicolor laccase and ortho-chlorophenol were strongest.HRP is a kind of peroxidase that contains hemoglobin.With hydrogen peroxide?H₂O₂?condition,HRP can promote oxidation conversation and coupling reaction of catalytic cycle and catalyze phenolic substance to form polymerization products.Although the catalytic process of HRP needs H₂O₂,HRP can promote the oxidation and removal of phenol pollutants effectively in a wide range of p H and temperature.The catalytic process of HRP includes three steps.The second step of peroxide cycle is the limited step and the third step can remove the product s.This research selected the second and third steps as the key steps to study the interactions in HRP peroxidation process.Although the experiments obtained the conversion rate of CP isomers in HRP/H₂O₂ system,the molecular mechanism has not been reported.Therefore,the study of the interactions between HRP compound I?or HRP compound II?and CPs can reveal the effect of chlorine substitution on reaction.Hydrogen bonds were beneficial to the stability of HRP and CPs complexes.The amino acid residues formed hydrogen bonds including Arg38,Ser73,Pro139 and His42.Hydrophobic effects were necessary in the binding of HRP to CPs.T he important amino acid residue involved in hydrophobic effects including Pro141 and Gly69.Additionally,the steric interactions were strongest in the binding of HRP to meta-chlorophenol,while the total interactions were strongest in the binding of HRP to para-chlorophenol.To investigate the molecular mechanism of pollutant degradation enzyme and phenolic pollutants using molecular docking can not only help to understand the degradation process of pollutants,but also can speculate the transformation and removal mechanism of pollutants with similar structures.It will be very important for pollution control and environmental protection.