Direct Fe2+ Sensing by Iron-responsive Messenger RNA·Repressor Complexes Weakens Binding*

AUTOR(ES)

Khan, Mateen A.

FONTE

American Society for Biochemistry and Molecular Biology

RESUMO

Fe2+ is now shown to weaken binding between ferritin and mitochondrial aconitase messenger RNA noncoding regulatory structures ((iron-responsive element) (IRE)-RNAs) and the regulatory proteins (IRPs), which adds a direct role of iron to regulation that can complement the well known regulatory protein modification and degradative pathways related to iron-induced mRNA translation. We observe that the Kd value increases 17-fold in 5′-untranslated region IRE-RNA·repressor complexes; Fe2+, is studied in the absence of O2. Other metal ions, Mn2+ and Mg2+ have similar effects to Fe2+ but the required Mg2+ concentration is 100 times greater than for Fe2+ or Mn2+. Metal ions also weaken ethidium bromide binding to IRE-RNA with no effect on IRP fluorescence, using Mn2+ as an O2-resistant surrogate for Fe2+, indicating that metal ions bound IRE-RNA but not IRP. Fe2+ decreases IRP repressor complex stability of ferritin IRE-RNA 5–10 times compared with 2–5 times for mitochondrial aconitase IRE-RNA, over the same concentration range, suggesting that differences among IRE-RNA structures contribute to the differences in the iron responses observed in vivo. The results show the IRE-RNA·repressor complex literally responds to Fe2+, selectively for each IRE-mRNA.

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