2005 Fiscal Year Final Research Report Summary
Elucidation of reaction mechanism based on the three-dimensional structures of heme oygenase reaction intermediates
| Project/Area Number |
16570095
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural biochemistry
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| Research Institution | Osaka University |
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Principal Investigator |
FUKUYAMA Keiichi Osaka University, Graduate School of Sciences, Professor, 大学院・理学研究科, 教授 (80032283)
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| Project Period (FY) |
2004 – 2005
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| Keywords | heme oxygenase / three-dimensional structure / X-ray analysis / photosynthetic pigments / ferredoxin |
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| Research Abstract |
Heme oxygenase (HO) is an essential enzyme in heme catabolism ; HO catalyzes heme cleavage at the α-position of heme using O_2 and reducing equivalents to produce biliverdin IXα,CO, and iron. In each of three sequential steps HO uses O_2 and in its second step CO is produced. Thus, HO should strictly discriminate O_2 and CO. We crystallographically pursued the behavier of CO photodissociated by laser from CO-heme-HO and clearly identified the site in HO which traps hydrophobic small molecules. This result reveals the molecular mechanism of escaping from product (CO) inhibition.
HO is indispensable for photosynthetic organisms. Red algae and cyanobacteria have phycobilisome containing bilin pigments which transfers photo-energy to photosystem II with high efficiency. These pigments are synthesyzed from biliverdin IXα by ferredoxin dependent bilin reductases. We determined the crystal structures of two HO isoforms from Synechocystis sp.PCC 6803 (Syn HO-1 and Syn HO-2). Syn heme-HO-1 had a fold similar to other HOs but the positively charged area on its surface was narrow. This feature may reflect the small size of the electron-transfer partner of ferredoxin. The structures of oxidized and reduced Syn heme-HO-2 and NO-heme-HO-2 demonstrated that NO was coordinated to the heme iron in bent form directing to α-meso carbon and that Syn heme-HO-2 forms a dimer. Gel chromatography suggested that it dimerize upon heme binding.
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Research Products
(13 results)
