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Redox-dependent axial ligand replacement and its functional significance in heme-bound iron regulatory proteins

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Title: Redox-dependent axial ligand replacement and its functional significance in heme-bound iron regulatory proteins
Authors: Ogura, Mariko Browse this author
Endo, Ryosuke Browse this author
Ishikawa, Haruto Browse this author
Takeda, Yukiko Browse this author
Uchida, Takeshi Browse this author →KAKEN DB
Iwai, Kazuhiro Browse this author
Kobayashi, Kazuo Browse this author
Ishimori, Koichiro Browse this author →KAKEN DB
Keywords: IRP
Ligand exchange
Resonance Raman
Pulse radiolysis
Issue Date: May-2018
Publisher: Elsevier
Journal Title: Journal of inorganic biochemistry
Volume: 182
Start Page: 238
End Page: 248
Publisher DOI: 10.1016/j.jinorgbio.2018.01.007
Abstract: Iron regulatory proteins (IRPs), regulators of iron metabolism in mammalian cells, control the translation of proteins involved in iron uptake, storage and utilization by binding to specific iron-responsive element (IRE) sequences of mRNAs. Two homologs of IRPs (IRP1 and IRP2) have a typical heme regulatory motif (HRM), a consensus sequence found in "heme-regulated proteins". However, specific heme binding to HRM has been reported only for IRP2, which is essential for oxidative modification and loss of binding to target mRNAs. In this paper, we confirmed that IRP1 also specifically binds two molar equivalents of heme, and found that the absorption and resonance Raman spectra of heme-bound IRP1 were quite similar to those of heme-bound IRP2. This shows that the heme environmental structures in IRP1 are close to those of proteins using heme as a regulatory molecule. Pulse radiolysis experiments, however, dearly revealed an axial ligand exchange from Cys to His immediately after the reduction of the heme iron to form a 5-coordinate His-ligated heme in heme-bound IRP2, whereas the 5-coordinate His-ligated heme was not observed after the reduction of heme-bound IRP1. Considering that the oxidative modification is only observed in heme-bound IRP2, but not IRP1, probably owing to the structural flexibility of IRP2, we propose that the transient 5 -coordinate His-ligated heme is a prerequisite for oxidative modification of heme-bound IRP2, which functionally differentiates heme binding of IRP2 from that of IRP1.
Rights: ©2018, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Type: article (author version)
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 石森 浩一郎

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