2005 Fiscal Year Final Research Report Summary
Structure and Function of Heme-regulated Proteins and Their Molecular Mechanisms
| Project/Area Number |
15350101
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Chemistry related to living body
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| Research Institution | Hokkaido University (2005)
Kyoto University (2003-2004) |
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Principal Investigator |
ISHIMORI Koichiro Hokkaido University, Division of Chemistry, Faculty of Science., Professor, 大学院理学研究科, 教授 (20192487)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Satoshi Osaka University, Institute for Protein, Associate Professor, 蛋白質研究所, 助教授 (30283641)
WAKASUGI Keisuke The University of Tokyo, Department of Life Science, Graduate School of Art and Science, Associated Professor, 大学院総合文化研究科, 助教授 (20322167)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Heme-regulated Protein / Iron Responsive Element / Irr / IRP2 / Replacement of Axial Ligands / Pulse Radiolysis / Resonance Raman / Heme Regulatory Motif |
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| Research Abstract |
The major results we have obtained in this research project are as follows:
1. Ligation of Cys to Ferric Heme in Irr and IRP2. Based on the resonance Raman spectra, we successfully identified the Fe-Cys stretching modes in ferric heme-bound Irr and IRP2. These Fe-Cys stretching modes were downshifted, compared with that in conventional Cys-ligated hemoproteins such as P450cam. The downshifted Fe-Cys stretching modes correspond to the lower affinities of these proteins to ferric heme, which is also supported by fluorescence heme titration in Irr. Such weak affinities of these proteins to heme would be one of the characteristics of heme-regulated proteins having "Heme Regulatory Motif'
2. Redox-dependent Replacement of Axial Ligands. We confirmed the ligation of Cys to ferric heme in Irr and IRP2. By reduction of the heme iron, however, the absorption spectra of heme-bound Irr and IRP2 were drastically changed and the resultant spectra were quite different from ferrous P450cam, which were rather similar to bis-His ligated hemoproteins like cytochrome b_5. The spectral similarity to His-ligated hemoprotein was more evident in the CO adducts of heme-bound Irr and IRP2. The resonance Raman measurements. clearly showed the Fe-His stretching modes in ferrous heme bound lrr and IRP2 and the Fe-C and FeC-O stretching modes in the CO adducts, confirming that axial Cys is replaced with His by reduction of the heme iron. Considering that molecular oxygen can bind to ferrous heme, not ferric heme, the His ligated species in these proteins would be active species to generate reactive oxygen species, which leads to the oxidative modification of the peptide and protein degradation.
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