1+1 = 3: a fusion of 2 enzymes in the methionine salvage pathway of Tetrahymena thermophila creates a trifunctional enzyme that catalyzes 3 steps in the pathway.
1+1 = 3: a fusion of 2 enzymes in the methionine salvage pathway of Tetrahymena thermophila creates a trifunctional enzyme that catalyzes 3 steps in the pathway.
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DOI：
10.1371/journal.pgen.1000701
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发表时间：
2009-10
期刊：
影响因子：
4.5
通讯作者：
Cavalcanti AR
中科院分区：
文献类型：
--
作者：
Salim HM;Negritto MC;Cavalcanti AR
甲硫氨酸补救途径负责从其衍生物甲硫腺苷再生甲硫氨酸。甲硫氨酸途径的全套酶先前已在细菌中描述。尽管其重要性，该途径仅在一种真核生物酵母中得到充分描述。在这里，我们使用计算的方法来确定在另一种真核生物，嗜热四膜虫甲硫氨酸补救途径的酶。在这种生物体中，该途径具有两个融合基因，MTNAK和MTNBD。每一种融合都涉及两种不同的基因，它们的产物在其他生物体中催化该途径的两个不同的单一步骤。其中一种融合蛋白mtnBD是由催化途径中的非连续步骤的酶mtnB和mtnD形成的。有趣的是，编码该途径中的中间酶mtnC的基因在四膜虫的基因组中缺失。我们在酵母中使用互补测试来表明，来自四膜虫的mtnB和mtnD的融合能够在一个步骤中完成酵母在三个步骤中所做的事情，因为它可以拯救mtnB，mtnC或mtnD的酵母敲除。融合基因已被证明是非常有用的帮助系统发育重建和基因的功能表征。我们的研究结果突出了融合蛋白的另一个特征，即这些蛋白质可以作为生化捷径，使生物体完全绕过生化途径中的步骤。由两个或多个其他基因的完整序列组成的融合基因是进化的极好标记。此外，融合基因通常由具有相关功能的基因组成，这使得当它们的一个组分的功能已知时，它们可用于推断功能。我们在真核生物嗜热四膜虫中检测到一个融合基因，虽然它只由两个基因组成，但似乎在这个生物体中执行三个基因的功能。为了证明这是事实，我们在三种不同的酵母菌株中表达了四膜虫融合基因，每种酵母菌株都缺乏这三种基因中的一种。四膜虫基因能够拯救所有酵母菌株的表型，证明它可以在酵母中执行三个基因的功能。我们的研究结果突出了融合基因的另一个重要的生化特征：它们可以作为生物捷径，允许两种酶的单一融合在功能上取代三种独立的酶。
The methionine salvage pathway is responsible for regenerating methionine from its derivative, methylthioadenosine. The complete set of enzymes of the methionine pathway has been previously described in bacteria. Despite its importance, the pathway has only been fully described in one eukaryotic organism, yeast. Here we use a computational approach to identify the enzymes of the methionine salvage pathway in another eukaryote, Tetrahymena thermophila. In this organism, the pathway has two fused genes, MTNAK and MTNBD. Each of these fusions involves two different genes whose products catalyze two different single steps of the pathway in other organisms. One of the fusion proteins, mtnBD, is formed by enzymes that catalyze non-consecutive steps in the pathway, mtnB and mtnD. Interestingly the gene that codes for the intervening enzyme in the pathway, mtnC, is missing from the genome of Tetrahymena. We used complementation tests in yeast to show that the fusion of mtnB and mtnD from Tetrahymena is able to do in one step what yeast does in three, since it can rescue yeast knockouts of mtnB, mtnC, or mtnD. Fusion genes have proved to be very useful in aiding phylogenetic reconstructions and in the functional characterization of genes. Our results highlight another characteristic of fusion proteins, namely that these proteins can serve as biochemical shortcuts, allowing organisms to completely bypass steps in biochemical pathways. Fusion genes, composed of the complete sequence of two or more other genes, are excellent markers of evolution. In addition, fused genes are usually composed of genes with related functions, which makes them useful in inferring function when the function of one of their components is known. We detected a fusion gene in the eukaryotic organism Tetrahymena thermophila that, although composed of only two genes, seems to perform the function of three genes in this organism. To show that this is the case, we expressed the Tetrahymena fused gene in three different yeast strains, each lacking one of these three genes. The Tetrahymena gene was able to rescue the phenotype of all yeast strains, proving that it can perform the functions of the three genes in yeast. Our results highlight another important biochemical characteristic of fusion genes: they can serve as biological shortcuts, allowing a single fusion of two enzymes to functionally replace three independent enzymes.
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影响因子：
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