1997 Fiscal Year Final Research Report Summary
Molecular Mechanism of Stereospecific Enzyme Reactions
| Project/Area Number |
07456049
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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 |
応用微生物学・応用生物化学
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| Research Institution | Nara Institute of Science and Technology |
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Principal Investigator |
HASHIMOTO Takashi NAIST,Biological Sciences, Associate Professor, バイオサイエンス研究科, 助教授 (80180826)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAJIMA Keiji NAIST,Biological Sciences, Research Associate, バイオサイエンス研究科, 助手 (80273853)
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| Project Period (FY) |
1995 – 1997
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| Keywords | stereospecificity / crystal structure / reductase / tropinone / alkaloid |
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| Research Abstract |
A pair of tropinone reductase (TRs) share 64% identical amino acid residues, and belong to the short-chain dehydrogenase/reductase family. In the synthesis of tropane alkaloids in several medicinal plants, the TRs reduce a carbonyl group of an alkaloid intermediate, tropinone, to hydroxy groups having different diastereomeric configurations. To clarify the structural basis for their different reaction stereospecificities, we determined the crystal structures of the two enzymes at 2.4- and 2.3-* resolutions. The overall folding of the two enzymes was almost identical. The conservation was not confined within the core domains which are conserved within the protein family, but also extended outside the core domain where each family member has its characteristic structure. The binding sites for the cofactor and the potitions of the active site residues were well conserved between the two TRs. The substrate binding site was composed mostly of hydrophobic amino acids in both TRs, but the presence of different charged residues conferred different electrostatic environments on the two enzymes. A modeling study indicated that these charged residues play a major role in controlling the binding orientation of tropinone within the substrate-binding site, thereby determining the stereospecificity of the reaction product. The results obtained raised the possibility that in certain cases novel stereospecificities can be acquired in emzymes by changing a few amino acid residues within substrate-binding sites.
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