| Project/Area Number |
09680619
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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 |
Functional biochemistry
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| Research Institution | Osaka University |
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Principal Investigator |
KURAMITSU Seiki Osaka University, Graduate School of Science Professor, 大学院・理学研究科, 教授 (60153368)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1998: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1997: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Keywords | Thermus thermophilus / aminotransferase / transferase / X-ray crystallography / lysine / substrate recognition mechanism / arginine / 蛋白質工学 / 酸性基質 / 変異型酵素 / カルボキシル基 / 基質結合部位 / X線結晶解析 / 疎水性基質 |
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| Research Abstract |
It has been believed that an enzyme is quite specific for its substrate.But aminotransferases are quite unique enzymes which can bind quite different binds of substrate.
These enzymes have two different types of binding pockets for acidic and hydrophobic substrates. (Catalytic residue is identical for each substrates.) Acidic substrate binds rigid region (Kawaguchi et al.(1997) J.Biochem.122, 55-63) and hydrophobic substrate binds flexible region (Kawaguchi and Kuramitsu, (1998) J.Biol. Chem. 273, 18353-18364).
The three-dimensional structure of aspartate aminotransferase from extreme thermophile, Thermus thermophilus HB8 have been determined by X-ray crystallography.In view of the X-ray crystallographic structure of T.thermophilus AspAT, K1O9V mutant was prepared.Replacing K109 with Val resulted in loss of activity toward acidic substrates, but increased that toward the neutral substrate, alanine, considerably.These results indicate that K109 is a major determinant of the acidic substrate specificity of T.thermophilus AspATs. Kinetic analysis of the interactions with neutral substrates indicated that T.thermophilus AspAT is subject to less steric hindrance and its substrate-binding pocket has a more flexible conformation than E.coli AspAT.A flexible active site in the rigid T.thermophilus AspAT molecule may explain its high activity even at room temperature.
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