A novel bifunctional N-acetylglutamate synthase-kinase from Xanthomonas campestris that is closely related to mammalian N-acetylglutamate synthase.
A novel bifunctional N-acetylglutamate synthase-kinase from Xanthomonas campestris that is closely related to mammalian N-acetylglutamate synthase.
复制标题
来自Xanthomonas campestris的新型双功能N-乙酰谷氨酸合酶 - 与哺乳动物N-乙酰谷氨酸合酶密切相关。
DOI：
10.1186/1471-2091-8-4
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发表时间：
2007-04-10
期刊：
影响因子：
--
通讯作者：
Caldovic, Ljubica
中科院分区：
文献类型：
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作者：
Qu, Qiuhao;Morizono, Hiroki;Shi, Dashuang;Tuchman, Mendel;Caldovic, Ljubica
在微生物和植物中，精氨酸生物合成的前两个反应由N-乙酰谷氨酸合酶（NAGS）和N-乙酰谷氨酸激酶（NAGK）催化。在哺乳动物中，NAGS是尿素循环的第一个酶氨甲酰磷酸合成酶I的重要激活剂，与其它尿素循环酶不同，哺乳动物的NAGS基因差异很大，是最后一个被发现的尿素循环基因。E. coliNAGS和真菌NAGK表明细菌和真核NAGS以及真菌NAGK是由编码祖先NAGK（argB）和乙酰转移酶的基因融合产生的。然而，哺乳动物NAGS不再保留任何NAGK催化活性。我们确定了一种新的双功能N-乙酰谷氨酸合酶和激酶（NAGS-K）的黄单胞菌目的γ-变形菌，似乎类似于这种假设的原始融合蛋白。系统发育分析表明，黄单胞菌NAGS-K与哺乳动物NAGS的亲缘关系较近。我们克隆了野疫黄单胞菌NAGS-K基因，并对重组蛋白进行了鉴定。哺乳动物NAGS及其细菌同系物对底物乙酰辅酶A和谷氨酸以及它们的变构调节剂精氨酸具有相似的亲和力。黄单胞菌NAGS-K与哺乳动物NAGS的亲缘关系较近，生化性质相似，提示我们已经鉴定出与哺乳动物NAGS的细菌前体有较近的亲缘关系。campestris可以作为哺乳动物NAGS结构、生化和生物物理研究的良好模型。
In microorganisms and plants, the first two reactions of arginine biosynthesis are catalyzed by N-acetylglutamate synthase (NAGS) and N-acetylglutamate kinase (NAGK). In mammals, NAGS produces an essential activator of carbamylphosphate synthetase I, the first enzyme of the urea cycle, and no functional NAGK homolog has been found. Unlike the other urea cycle enzymes, whose bacterial counterparts could be readily identified by their sequence conservation with arginine biosynthetic enzymes, mammalian NAGS gene was very divergent, making it the last urea cycle gene to be discovered. Limited sequence similarity between E. coli NAGS and fungal NAGK suggests that bacterial and eukaryotic NAGS, and fungal NAGK arose from the fusion of genes encoding an ancestral NAGK (argB) and an acetyltransferase. However, mammalian NAGS no longer retains any NAGK catalytic activity. We identified a novel bifunctional N-acetylglutamate synthase and kinase (NAGS-K) in the Xanthomonadales order of gamma-proteobacteria that appears to resemble this postulated primordial fusion protein. Phylogenetic analysis indicated that xanthomonad NAGS-K is more closely related to mammalian NAGS than to other bacterial NAGS. We cloned the NAGS-K gene from Xanthomonas campestis, and characterized the recombinant NAGS-K protein. Mammalian NAGS and its bacterial homolog have similar affinities for substrates acetyl coenzyme A and glutamate as well as for their allosteric regulator arginine. The close phylogenetic relationship and similar biochemical properties of xanthomonad NAGS-K and mammalian NAGS suggest that we have identified a close relative to the bacterial antecedent of mammalian NAGS and that the enzyme from X. campestris could become a good model for mammalian NAGS in structural, biochemical and biophysical studies.