Identification of a Critical Amino Acid in the Aryl Hydrocarbon Receptor

• Published in: The Journal of biological chemistry Vol. 277; no. 15; pp. 13210 - 13218
• Main Authors: Andreasen, Eric A., Tanguay, Robert L., Peterson, Richard E., Heideman, Warren
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 12.04.2002; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Amino Acid Substitution; Amino Acids - metabolism; Animals; Base Sequence; COS Cells; DNA Primers; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Oncorhynchus mykiss; Protein Conformation; Receptors, Aryl Hydrocarbon - chemistry; Receptors, Aryl Hydrocarbon - genetics; Receptors, Aryl Hydrocarbon - metabolism; Sequence Homology, Amino Acid
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M200073200

Two aryl hydrocarbon receptors (rtAHR2α and rtAHR2β) have been identified in the rainbow trout (Oncorhynchus mykiss). These receptors share 98% amino acid identity, yet their functional properties differ. Both rtAHR2α and rtAHR2β bind 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), dimerize with rainbow trout ARNTb (rtARNTb), and recognize dioxin response elements in vitro. However, in a transient transfection assay the two proteins show differential ability to recognize enhancers, produce transactivation, and respond to TCDD. To identify the sequence differences that confer the functional differences between rtAHR2α and rtAHR2β, we constructed chimeric rtAHRs, in which segments of one receptor form was replaced with the corresponding part from the other isoform. This approach progressively narrowed the region being examined to a single residue, corresponding to position 111 in rtAHR2β. Altering this residue in rtAHR2β from the lysine to glutamate found in rtAHR2α produced an rtAHR2β with the properties of rtAHR2α. All other known AHRs resemble rtAHR2α and carry glutamate at this position, located at the N terminus of the PAS-A domain. We tested the effect of altering this glutamate in the human and zebrafish AHRs to lysine. This lysine substitution produced AHRs with transactivation properties that were similar to rtAHR2β. These results identify a critical residue in AHR proteins that has an important impact on transactivation, enhancer site recognition, and regulation by ligand.