Fenalti Gustavo, Law Ruby H P, Buckle Ashley M, Langendorf Christopher, Tuck Kellie, Rosado Carlos J, Faux Noel G, Mahmood Khalid, Hampe Christiane S, Banga J Paul, Wilce Matthew, Schmidberger Jason, Rossjohn Jamie, El-Kabbani Ossama, Pike Robert N, Smith A Ian, Mackay Ian R, Rowley Merrill J, Whisstock James C
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Melbourne, VIC 3800, Australia.
Nat Struct Mol Biol. 2007 Apr;14(4):280-6. doi: 10.1038/nsmb1228. Epub 2007 Mar 25.
Gamma-aminobutyric acid (GABA) is synthesized by two isoforms of the pyridoxal 5'-phosphate-dependent enzyme glutamic acid decarboxylase (GAD65 and GAD67). GAD67 is constitutively active and is responsible for basal GABA production. In contrast, GAD65, an autoantigen in type I diabetes, is transiently activated in response to the demand for extra GABA in neurotransmission, and cycles between an active holo form and an inactive apo form. We have determined the crystal structures of N-terminal truncations of both GAD isoforms. The structure of GAD67 shows a tethered loop covering the active site, providing a catalytic environment that sustains GABA production. In contrast, the same catalytic loop is inherently mobile in GAD65. Kinetic studies suggest that mobility in the catalytic loop promotes a side reaction that results in cofactor release and GAD65 autoinactivation. These data reveal the molecular basis for regulation of GABA homeostasis.
γ-氨基丁酸（GABA）由依赖磷酸吡哆醛的谷氨酸脱羧酶的两种同工型（GAD65和GAD67）合成。GAD67组成性激活，负责基础GABA的产生。相比之下，GAD65是I型糖尿病中的自身抗原，在神经传递中对额外GABA的需求响应下被短暂激活，并在活性全酶形式和无活性脱辅基形式之间循环。我们已经确定了两种GAD同工型N端截短体的晶体结构。GAD67的结构显示一个覆盖活性位点的拴系环，提供了维持GABA产生的催化环境。相比之下，相同的催化环在GAD65中固有地可移动。动力学研究表明，催化环中的移动性促进了导致辅因子释放和GAD65自失活的副反应。这些数据揭示了GABA稳态调节的分子基础。
