Nuclear Receptors Homo sapiens Rev-erbβ and Drosophila melanogaster E75 Are Thiolate-Ligated Heme Proteins Which Undergo Redox-Mediated Ligand Switching and Bind CO and NO

• Published in: Biochemistry (Easton) Vol. 48; no. 29; pp. 7056 - 7071
• Main Authors: Marvin, Katherine A, Reinking, Jeffrey L, Lee, Andrea J, Pardee, Keith, Krause, Henry M, Burstyn, Judith N
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28-07-2009
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi900697c

Nuclear receptors E75, which regulates development in Drosophila melanogaster, and Rev-erbβ, which regulates circadian rhythm in humans, bind heme within their ligand binding domains (LBD). The heme-bound ligand binding domains of E75 and Rev-erbβ were studied using electronic absorption, MCD, resonance Raman, and EPR spectroscopies. Both proteins undergo redox-dependent ligand switching and CO- and NO-induced ligand displacement. In the Fe(III) oxidation state, the nuclear receptor hemes are low spin and 6-coordinate with cysteine(thiolate) as one of the two axial heme ligands. The sixth ligand is a neutral donor, presumably histidine. When the heme is reduced to the Fe(II) oxidation state, the cysteine(thiolate) is replaced by a different neutral donor ligand, whose identity is not known. CO binds to the Fe(II) heme in both E75(LBD) and Rev-erbβ(LBD) opposite a sixth neutral ligand, plausibly the same histidine that served as the sixth ligand in the Fe(III) state. NO binds to the heme of both proteins; however, the NO−heme is 5-coordinate in E75 and 6-coordinate in Rev-erbβ. These nuclear receptors exhibit coordination characteristics that are similar to other known redox and gas sensors, suggesting that E75 and Rev-erbβ may function in heme-, redox-, or gas-regulated control of cellular function.