1992 Fiscal Year Final Research Report Summary
Structural studies on relationship between the flexibility of loop and the function of enzyme
| Project/Area Number |
03680048
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
結晶学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
HATA Yasuo Kyoto University, Institute for Chemical Research, Associate professor, 化学研究所, 助教授 (10127277)
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| Project Period (FY) |
1991 – 1992
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| Keywords | flexible loop / fluctuation of loop / structure analysis / ATP / glutathione synthetase |
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| Research Abstract |
X-ray analysis of glutathione synthetase from Escherichia coli B which catalyzes the synthesis of glutathione from gamma-L-Glu-L-Cys and Gly in the presence of ATP and magnesium ion revealed that Ile226-Gly241 of the enzyme had an flexible loop structure which was unvisible in the electron density map. It was expected that this loop may exist near the substrate binding sites and play an important role in the enzymatic reaction. Then, structural studies on the role of the flexible loop in the reaction were carried out using specific cleavage of the loop by arginylendopeptidase, mutational analysis and chemical modification. It turned out that the flexible loop is essential to the substrate binding as well as the enzyme reaction. The high-energy bonds in ATP and acylphosphate intermediate are quite sensitive against nucleophilic attack. If a water molecule reacts with ATP instead of a proper reactant, ATP ishydrolyzed by the water and then the enzymatic reaction does not proceed properly toward the preferable product. The flexible loop may protect the intermediate or the enzyme-substrate complex from undesirable reactions which may take place through interaction of the intermediate or the complexes with water. When the substrates bind to the enzyme, the flexible loop seems to protect the substrates from any attack of water by changing its conformation to wrape their binding sites. The function of the loop in glutathione synthetase seems to be similar to that in triosephosphate isomerase. Detailed information on the reaction mechanism of the enzyme will be obtained by time-resolved Laue experiments using synchrotron radiation.
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