Structure of aspartoacylase, the brain enzyme impaired in Canavan disease
Structure of aspartoacylase, the brain enzyme impaired in Canavan disease
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DOI：
10.1073/pnas.0607817104
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发表时间：
2007-01-09
影响因子：
11.1
通讯作者：
Phillips, George N., Jr.
中科院分区：
文献类型：
--
作者：
Bitto, Eduard;Bingman, Craig A.;Phillips, George N., Jr.
在脊椎动物的大脑中，天冬氨酸氨基转移酶催化N-乙酰-L-天冬氨酸的水解制得天冬氨酸和乙酸乙酯。这一活动的缺乏会导致脑白质海绵状变性，是影响幼儿的致命进行性脑白质营养不良加那文病的确定原因。我们给出了分别细化到2.8埃和1.8埃分辨率的重组人和大鼠天冬氨酸氨基转移酶的晶体结构。结果表明，天冬氨酸氨基转移酶的N-末端结构域具有与羧基肽酶A相关的锌依赖水解酶相似的蛋白质折叠结构。天冬氨酸氨基转移酶的催化部位与羧基肽酶的催化部位在结构上非常相似，尽管它们之间的序列相似性只有10-13%。大约100个天冬氨酸酰基酶的C-末端残基形成一个球状结构域，它带有一个包裹在N-末端结构域周围的双链β-折叠接头。N-末端结构域和C-末端结构域的界面形成了通向活性中心的长通道。C-末端结构域以阻止活性部位中多肽的有效结合的方式定位。结构表明，残基158-164可能发生构象变化，导致通道入口打开和部分关闭。我们假设天冬氨酸酰基酶的催化机理与羧基肽酶的催化机理非常相似。我们确定了参与锌配位的残基，并提出了哪些残基可能参与底物结合和催化。这些结构还提供了一个必要的结构框架，以了解许多人类天冬氨酸氨基转移酶错义突变的有害影响。
Aspartoacylase catalyzes hydrolysis of N-acetyl-L-aspartate to aspartate and acetate in the vertebrate brain. Deficiency in this activity leads to spongiform degeneration of the white matter of the brain and is the established cause of Canavan disease, a fatal progressive leukodystrophy affecting young children. We present crystal structures of recombinant human and rat aspartoacylase refined to 2.8- and 1.8-angstrom resolution, respectively. The structures revealed that the N-terminal domain of aspartoacylase adopts a protein fold similar to that of zinc-dependent hydrolases related to carboxypepticlases A. The catalytic site of aspartoacylase shows close structural similarity to those of carboxypeptidases despite only 10-13% sequence identity between these proteins. About 100 C-terminal residues of aspartoacylase form a globular domain with a two-stranded beta-sheet linker that wraps around the N-terminal domain. The long channel leading to the active site is formed by the interface of the N- and C-terminal domains. The C-terminal domain is positioned in a way that prevents productive binding of polypetides in the active site. The structures revealed that residues 158-164 may undergo a conformational change that results in opening and partial closing of the channel entrance. We hypothesize that the catalytic mechanism of aspartoacylase is closely analogous to that of carboxypepticlases. We identify residues involved in zinc coordination, and propose which residues may be involved in substrate binding and catalysis. The structures also provide a structural framework necessary for understanding the deleterious effects of many missense mutations of human aspartoacylase.