The tertiary structures of porcine AhR and ARNT proteins and molecular interactions within the TCDD/AhR/ARNT complex

• The protein structures of porcine AhR and ARNT were modeled in silico.
• TCDD was docked into the ligand binding pocket of the AhR.
• Molecular interactions between AhR and ARNT were examined.
• Transcriptional activity of the TCDD-AhR-ARNT complex was investigated.

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that can be activated by structurally diverse synthetic and natural chemicals, including toxic environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In the present study, homology models of the porcine AhR-ligand binding domain (LBD) and the porcine aryl hydrocarbon receptor nuclear translocator-ligand binding domain (ARNT-LBD) were created on the basis of structures of closely related respective proteins i.e., human Hif-2α and ARNT. Molecular docking of TCDD to the porcine AhR-LBD model revealed high binding affinity (−8.8 kcal/mol) between TCDD and the receptor. Moreover, formation of the TCDD/AhR-LBD complex was confirmed experimentally with the use of electrophoretic mobility shift assay (EMSA). It was found that TCDD (10 nM, 2 h of incubation) not only bound to the AhR in the porcine granulosa cells but also activated the receptor. The current study provides a framework for examining the key events involved in the ligand-dependent activation of the AhR.

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