2005 Fiscal Year Final Research Report Summary
Structure and function of PLP-dependent enzyme and its homolog involved in higher brain functions
| Project/Area Number |
16370053
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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 |
Structural biochemistry
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| Research Institution | Osaka City University |
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Principal Investigator |
HIROTSU Ken Osaka city University, Graduate School of Science, Professor, 大学院・理学研究科, 特任教授 (10047269)
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| Co-Investigator(Kenkyū-buntansha) |
MIYAHARA Ikuko Osaka city University, Graduate School of Science, lecturer, 大学院・理学研究科, 講師 (40271176)
ESAKI Nobuyoshi Kyoto University, Institute for Chemical Research, Professor, 化学研究所, 教授 (50135597)
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| Project Period (FY) |
2004 – 2005
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| Keywords | branched chain aminotransferase / gabapenchin / neuroactive drug / D-serine / serine racemase / NMDA acceptor / PLP-dependent enzyme / X-ray structure |
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| Research Abstract |
The branched chain aminotransferases reversibly catalyzes transamination of the essential branched chain amino acids to α-ketoglutarate to form the respective branched chain α-keto acid and glutamate. The cytosolic isozyme is predominant in the nervous system and is inhibited by gabapentin. 1.3 mM gabapentin can completely inhibit the binding of leucine to cytosolic isozyme whereas 65.4 mM gabapentin is required to inhibit leucine binding to mitochondrial isozyme. This study presents the first three-dimensional structure of human cytosolic isozyme complexed with the neuroactive drug gabapentin. Structural analysis shows that the bulky gabapentin is enclosed in the active-site cavity by the shift of a flexible loop that enlarges the active-site cavity. The specificity of gabapentin for cytosolic isozyme is ascribed at least in part to the location of the interdomain loop and the relative orientation between the small and large domain which is different from these relationships in the mi
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tochondrial isozyme.
D-serine is an endogenous coagonist for NMDA receptor and is involved in excitatory neurotransmission in the brain. The mammalian PLP-dependent serine racemase, which is localized at protoplasmic astrocytes, catalyzes the racemization of L-Ser to yield D-Ser. The reaction is strongly stimulated by Mg・ATP in vivo. Three-dimensional structures of the mammalian enzyme homolog from Schizosaccharomyces pombe have been determined. The binding of ATP analog alter the relative orientation of the subunits without changing the subunit conformation. The cofactor is connected to the ATP analog through a complicated hydrogen bonding network. Unexpectedly, the closed form presents the unique ‘cofactor-D-alanine-Lys-57' covalent bond structure at the active site, indicating that the covalent bond structure functions as an active center. The computer graphics models of the L-Ser and D-Ser complex clarified the substrate recognition mechanism and gave an insight into the catalytic mechanism of both reactions. Less
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