Ferritin overcomes the 10(-13-)-fold mismatch between iron needs and solubility by concentrating iron as a solid mineral. High ferritin expression in erythrocytes of the embryonic cell line, plus easy access to embryonic red cells in tadpoles, led to the frog model. Frog iron metabolism accurately models humans; studying common features assures fundamental biological significance and health relatedness. Iron is mineralized in a commodious cavity of iso-ferritins created by mixtures of 24 (H, L, H+L, H+L+M) protein subunits. Iron ions are translocated through the protein, to and from the cavity. Ferritin expression is precisely is precisely regulated, using both DNA and mRNA targets. Red cell ferritin is coordinately regulated with erythroid aminolevulinate (eALAS), the transferrin receptor (TfR) [Nramp2?] via the mRNA iso-elements (IREs), and a family of IRE recognition proteins, (IRPs). The wide range of ferritin function and regulation possible emphasize the central role of iron in red cells and other cells. During the last grant period the major results obtained were: 1- mRNA (IRE/IRP). a) NMR structure and model of the ferritin-IRE; b) identification of IRE isoform structure and differential IRP + binding; c) Targeting mRNA of the ferritin-IRE; b) Identification of IRE isoform structure and differential IRP + binding; C) Targeting mRNA o with a TMC in vivo; 2- Ferritin protein: a) Identification of new intermediates in ferritin mineralization: diferric peroxo decay, and tri-iron clusters; b) Location of a ferritin protein site where iron exits, a new target for iron chelation. 3-Ferritin genes and iron nutrition: a) Dietary ferritin, pure or in soybeans, cured iron deficiency anemia in rats. b) Characterizing soybean ferritin genes, to improve seed iron composition, showed the absence of the IRE. Both the newly identified ferritin DNA promoter in plants and mRNA """"""""promoter"""""""" in animals responded to the same signals, emphasizing the fundamental chemistry of iron/oxygen in biology and the central significance of ferritin signals, emphasizing the fundamental chemistry of iron/oxygen in biology and the central significance of ferritin.
Specific aims proposed are: 1-Iso-Ire structure/function. Effects of IRE subdomains of ferritin synthesis, mRNA stability, Tm (+/- metals) and nuclease cleavage related to IRP1/IRP2 binding in vitro and in vivo 2. Ferritin function-iron uptake and release related to cellular iron metabolism: Effects of engineered H and L type subunits on iron uptake and release in vitro (UV-vis, RFQ Mossbauer, RR, ENDOR and EXAFS and X-ray crystallography) and in vivo. 3. Iso- IRE/protein """"""""footprint"""""""" interactions in vivo. Long term goals are the targeting of ferritin mRNA and protein for therapies in iron overload and targeting mRNAs in viral and oncogenic diseases.
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