Substrate specificity and structure of human aminoadipate aminotransferase/kynurenine aminotransferase II.
Substrate specificity and structure of human aminoadipate aminotransferase/kynurenine aminotransferase II.
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DOI：
10.1042/bsr20080085
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发表时间：
2008-08
影响因子：
4
通讯作者：
Li J
中科院分区：
文献类型：
--
作者：
Han Q;Cai T;Tagle DA;Robinson H;Li J
KAT（犬尿氨酸转氨酶）II是脑内催化犬尿氨酸转氨化成KYNA（犬尿氨酸酸）的主要酶。KYNA是唯一已知的n -甲基-d-天冬氨酸受体内源性拮抗剂。该酶还能催化氨基己二酸转化为α-氧己二酸；因此它最初被命名为AADAT（氨基己二酸转氨酶）。作为一种内毒素，氨基己二酸影响谷氨酸能神经传递的各种成分，并杀死脑内的初级星形胶质细胞。文献中有许多关于该酶的生化和功能特征的研究，但尚未对KAT II进行系统评估，以解决其底物特征和动力学性质。本研究探讨了人类KAT II/AADAT的生化和结构特征。人KAT II的底物筛选表明，该酶具有非常广泛的底物特异性，能够催化24种测试氨基酸中的16种转氨作用，并且可以利用所有16种测试的α-氧酸作为氨基受体。人KAT II的动力学分析表明其对单个氨基供体和受体的催化效率，提供了其首选底物亲和力的信息。对α-氧戊二酸人KAT II配合物的结构分析显示，n端残基15-33的构象发生了变化，能够适应不同的底物大小，这为其广泛的底物特异性提供了结构基础。
KAT (kynurenine aminotransferase) II is a primary enzyme in the brain for catalysing the transamination of kynurenine to KYNA (kynurenic acid). KYNA is the only known endogenous antagonist of the N-methyl-d-aspartate receptor. The enzyme also catalyses the transamination of aminoadipate to α-oxoadipate; therefore it was initially named AADAT (aminoadipate aminotransferase). As an endotoxin, aminoadipate influences various elements of glutamatergic neurotransmission and kills primary astrocytes in the brain. A number of studies dealing with the biochemical and functional characteristics of this enzyme exist in the literature, but a systematic assessment of KAT II addressing its substrate profile and kinetic properties has not been performed. The present study examines the biochemical and structural characterization of a human KAT II/AADAT. Substrate screening of human KAT II revealed that the enzyme has a very broad substrate specificity, is capable of catalysing the transamination of 16 out of 24 tested amino acids and could utilize all 16 tested α-oxo acids as amino-group acceptors. Kinetic analysis of human KAT II demonstrated its catalytic efficiency for individual amino-group donors and acceptors, providing information as to its preferred substrate affinity. Structural analysis of the human KAT II complex with α-oxoglutaric acid revealed a conformational change of an N-terminal fraction, residues 15-33, that is able to adapt to different substrate sizes, which provides a structural basis for its broad substrate specificity.