title: A novel heme-regulatory motif mediates heme-dependent degradation of the circadian factor period 2.
abstract: Although efforts have been made to identify circadian-controlled genes regulating cell cycle progression and cell death, little is known about the metabolic signals modulating circadian regulation of gene expression. We identify heme, an iron-containing prosthetic group, as a regulatory ligand controlling human Period-2 (hPer2) stability. Furthermore, we define a novel heme-regulatory motif within the C terminus of hPer2 (SC(841)PA) as necessary for heme binding and protein destabilization. Spectroscopy reveals that whereas the PAS domain binds to both the ferric and ferrous forms of heme, SC(841)PA binds exclusively to ferric heme, thus acting as a redox sensor. Consequently, binding prevents hPer2 from interacting with its stabilizing counterpart cryptochrome. In vivo, hPer2 downregulation is suppressed by inhibitors of heme synthesis or proteasome activity, while SA(841)PA is sufficient to stabilize hPer2 in transfected cells. Moreover, heme binding to the SC(841)PA motif directly impacts circadian gene expression, resulting in altered period length. Overall, the data support a model where heme-mediated oxidation triggers hPer2 degradation, thus controlling heterodimerization and ultimately gene transcription.
authors.affiliation: Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Yang
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Kim
authors.forename: Andrew
authors.initials: A
authors.lastname: Lucas
authors.forename: Karen E
authors.initials: KE
authors.lastname: Drahos
authors.forename: Carlo S
authors.initials: CS
authors.lastname: Santos
authors.forename: Sean P
authors.initials: SP
authors.lastname: Mury
authors.forename: Daniel G S
authors.initials: DG
authors.lastname: Capelluto
authors.forename: Carla V
authors.initials: CV
authors.lastname: Finkielstein
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002940:Circadian Rhythm / Q000187:drug effects* / Q000235:genetics; D002942:Circular Dichroism; D006224:Cricetinae; D003412:Cricetulus; D056931:Cryptochromes; D019281:Dimerization; D005420:Flavoproteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006367:HeLa Cells; D006418:Heme / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D056950:Period Circadian Proteins; D011485:Protein Binding / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D017434:Protein Structure, Tertiary; D013816:Thermodynamics; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D056931:Cryptochromes; D005420:Flavoproteins; D009687:Nuclear Proteins; C421902:PER2 protein, human; D056950:Period Circadian Proteins; D014157:Transcription Factors; D006418:Heme