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Brain serine racemase contains pyridoxal phosphate as a prosthetic group and is known to become activated by divalent cations such as Ca 2+ and Mg2+ , as well as by ATP and ADP. In vivo, brain serine racemase is also activated by a multi-PSD-95⁄discs large⁄ZO-1 (PDZ) domain glutamate receptor interacting protein (GRIP) that is usually coupled to the GluR2⁄3 subunits of the a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid Ca 2+ channel. | ỊFEBS Journal Insights into the activation of brain serine racemase by the multi-PDZ domain glutamate receptor interacting protein divalent cations and ATP Florian Baumgart1 Jose M. Mancheno2 and Ignacio Rodriguez-Crespo1 1 Departamento de Bioquimica y Biologia Molecular Facultad de Ciencias Quimicas Universidad Complutense de Madrid Spain 2 Grupo de Cristalografia Macromolecular y Biologia Estructural Instituto Rocasolano CSIC Madrid Spain Keywords calcium activation D-serine GRIP PDZ domain serine racemase Correspondence I. Rodriguez-Crespo Departamento de Bioquimica y Biologia Molecular Facultad de Ciencias Quimicas Universidad Complutense 28040 Madrid Spain Fax 34 91 394 4159 Tel 34 91 394 4137 E-mail nacho@bbm1.ucm.es Received 7 June 2007 revised 6 July 2007 accepted 11 July 2007 doi 10.1111 j.1742-4658.2007.05986.x Brain serine racemase contains pyridoxal phosphate as a prosthetic group and is known to become activated by divalent cations such as Ca2 and Mg2 as well as by ATP and ADP. In vivo brain serine racemase is also activated by a multi-PSD-95 discs large ZO-1 PDZ domain glutamate receptor interacting protein GRIP that is usually coupled to the GluR2 3 subunits of the a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid Ca2 channel. In the present study we analysed the mechanisms by which serine racemase becomes activated by GRIP divalent cations and ATP. We show that binding of PDZ6 of GRIP to serine racemase does not result in increased D-serine production. However full-length GRIP does augment significantly enzymatic activity. We expressed various GRIP shorter constructs to map down the regions within GRIP that are necessary for serine racemase activation. We observed that whereas recombinant proteins containing PDZ4-PDZ5-PDZ6 are unable to activate serine racemase other constructs containing PDZ4-PDZ5-PDZ6-GAP2-PDZ7 significantly augment its activity. Hence activation of serine racemase by GRIP is not a direct consequence of the translocation .
