title: Fe2+ binds iron responsive element-RNA, selectively changing protein-binding affinities and regulating mRNA repression and activation.
abstract: Iron increases synthesis rates of proteins encoded in iron-responsive element (IRE)-mRNAs; metabolic iron ("free," "labile") is Fe(2+). The noncoding IRE-RNA structure, approximately 30 nt, folds into a stem loop to control synthesis of proteins in iron trafficking, cell cycling, and nervous system function. IRE-RNA riboregulators bind specifically to iron-regulatory proteins (IRP) proteins, inhibiting ribosome binding. Deletion of the IRE-RNA from an mRNA decreases both IRP binding and IRP-independent protein synthesis, indicating effects of other "factors." Current models of IRE-mRNA regulation, emphasizing iron-dependent degradation/modification of IRP, lack answers about how iron increases IRE-RNA/IRP protein dissociation or how IRE-RNA, after IRP dissociation, influences protein synthesis rates. However, we observed Fe(2+) (anaerobic) or Mn(2+) selectively increase the IRE-RNA/IRP K(D). Here we show: (i) Fe(2+) binds to the IRE-RNA, altering its conformation (by 2-aminopurine fluorescence and ethidium bromide displacement); (ii) metal ions increase translation of IRE-mRNA in vitro; (iii) eukaryotic initiation factor (eIF)4F binds specifically with high affinity to IRE-RNA; (iv) Fe(2+) increased eIF4F/IRE-RNA binding, which outcompetes IRP binding; (v) exogenous eIF4F rescued metal-dependent IRE-RNA translation in eIF4F-depeleted extracts. The regulation by metabolic iron binding to IRE-RNA to decrease inhibitor protein (IRP) binding and increase activator protein (eIF4F) binding identifies IRE-RNA as a riboregulator.
authors.affiliation: Department of Chemistry, Hunter College and the Graduate Center City University of New York, 695 Park Ave, New York, NY 10065, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Ma
authors.forename: Suranjana
authors.initials: S
authors.lastname: Haldar
authors.forename: Mateen A
authors.initials: MA
authors.lastname: Khan
authors.forename: Sohani Das
authors.initials: SD
authors.lastname: Sharma
authors.forename: William C
authors.initials: WC
authors.lastname: Merrick
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Theil
authors.forename: Dixie J
authors.initials: DJ
authors.lastname: Goss
mesh_terms: D015075:2-Aminopurine / Q000737:chemistry; D001483:Base Sequence; D001665:Binding Sites; D004996:Ethidium / Q000737:chemistry; D039562:Eukaryotic Initiation Factor-4F / Q000737:chemistry / Q000378:metabolism; D005786:Gene Expression Regulation; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D035925:Iron-Regulatory Proteins / Q000737:chemistry / Q000378:metabolism*; D008957:Models, Genetic; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements
chemical_list: D039562:Eukaryotic Initiation Factor-4F; D035925:Iron-Regulatory Proteins; D012333:RNA, Messenger; D015075:2-Aminopurine; D012313:RNA; D007501:Iron; D004996:Ethidium