Interaction Study Of Ionizable Organic Compounds And Metal Ions Binding To Transthyretin

The effects of endocrine-disrupting chemicals（EDCs）on organisms have received increasing attention.One of the interference mechanisms of EDCs on the endocrine system is the effect on hormone transport.There are more than 140,000 compounds used in commerce.About 50%of the compounds have ionizable groups,and the toxicity of these compounds in their neutral and ionic forms is different.It is necessary to study the toxicity of ionizable compounds.Human transthyretin（h TTR）is an important transporter in the blood.Many people have studied the effect of different compounds on h TTR,but little research has been done on the binding ability of ionizable compounds halo-phenylboronic acid,halo-benzoic acid,and halo-benzenesulfonic acid/sulfate to h TTR.Metal ions are trace elements that play a vital role in human life.What effect they have on the binding of ionizable compounds to h TTR has not been studied.In this study,we analyzed the interactions and mechanisms of three types of ionizable compounds with h TTR by combining fluorescent competitive substitution methods with computational methods.We studied the binding capacity of metal ions to compounds by fluorescent competitive substitution method.The research results are as follows:All the tested halo-phenylboronic acids,partial tested halo-benzoic acids and halo-benzenesulfonic acids/sulfates were inactive h TTR binders.Other halo-benzoic acids and halo-benzenesulfonic acids/sulfates were moderate and/or low potency h TTR binders.The binding affinity of halo-benzoic acids and halo-benzenesulfonic acids/sulfates with h TTR were similar.The low distribution ability of the model compounds from water to h TTR may be the reason why they exhibited the binding potency observed with h TTR.By introducing other high hydrophobicity compounds,we observed that the binding affinity between compounds and h TTR increased with the increase of molecular hydrophobicity.Those results indicated that the highly hydrophobic halo-benzoic acids and halo-benzenesulfonic acids may be high-priority h TTR disruptors.Finally,a binary classification model was constructed employing three predictive variables to predict whether ionizable compounds would bind to h TTR.The sensitivity（Sn）,specificity（Sp）,predictive accuracy（Q）values of the training set and validation set were>0.83,indicating the model has good classification performance.Thus,the binary classification model developed here could be used to distinguish whether a given ionizable compounds is potential h TTR binder or not.The interaction of seven metal ions(Copper(Cu²⁺),zinc(Zn²⁺),cobalt(Co²⁺),chromium(Cr³⁺),cadmium(Cd²⁺),lithium（Li⁺）,lead(Pb²⁺))was tested.The results show that both Cu²⁺and Zn²⁺can interact with h TTR,while Co²⁺,Cr³⁺,Cd²⁺,Li⁺,Pb²⁺had no effect on the combination of ionizable compounds with h TTR.The interaction between Cu²⁺and h TTR weakened its fluorescence intensity,and the interaction between Zn²⁺and h TTR increased its fluorescence intensity.The effects of Cu²⁺and Zn²⁺on the binding ability of T4 and ionizable compounds（2,4,6-tribromophenol（high binding potency）,2,4,6-tribromobenzoic acid（low binding potency））to h TTR were also studied.Cu²⁺enhanced the binding ability of 2,4,6-tribromophenol,2,4,6-tribromobenzoic acid and h TTR.Zn²⁺weakened the binding ability of2,4,6-tribromophenol to h TTR and had no effect on the binding ability of 2,4,6-tribromobenzoic acid.