A theoretical investigation of the conformation changing of dioxins in the binding site of dioxin receptor model; role of absolute hardness-electronegativity activity diagrams for biological activity

To investigate the interaction with the binding site of dioxin receptor of dioxins, we analyzed the structure and energy for the 2,3,7,8-TCDD- and 1,4,6,9-TCDD-amino acid residue complex, respectively, by calculation using the semiempirical AM1 method. It was found that the glutamine residue plays an important role in the formation of an energetically stable complex with dioxin. Particularly, toxic 2,3,7,8-TCDD is easily bound with the dioxin receptor, and the complex is nearly planar and most energerically stable. However, the structure of 1,4,6,9-TCDD is folded, and the value of absolute hardness increases. This means that 2,3,7,8-TCDD binds with the dioxin receptor more strongly than 1,4,6,9-TCDD. As a result, we propose a dioxin binding site model, -Asn-Phe-Gln(-CONH2 ... 2,3,7,8-TCDD)-Gly-Arg-. We conclude that the eta-chi activity diagram can apply to the model of the ligand binding site in the dioxin receptor. (C) 1999 Elsevier Science B.V. All rights reserved.