A novel ferredoxin-dependent glutamate synthase from the hydrogen-oxidizing chemoautotrophic bacterium Hydrogenobacter thermophilus TK-6
A novel ferredoxin-dependent glutamate synthase from the hydrogen-oxidizing chemoautotrophic bacterium Hydrogenobacter thermophilus TK-6
复制标题
DOI：
10.1128/jb.01360-06
复制
发表时间：
2007-04-01
影响因子：
3.2
通讯作者：
Igarashi, Yasuo
中科院分区：
文献类型：
--
作者：
Kameya, Masafumi;Ikeda, Takeshi;Igarashi, Yasuo
谷氨酸脱氢酶根据其对电子供体的特异性进行分类。铁氧还蛋白依赖的谷氨酸脱氢酶仅在植物和蓝藻中发现，而许多细菌都有NADPH依赖的谷氨酸脱氢酶。在这项研究中，嗜热氢杆菌，氢氧化化能自养细菌，被证明具有铁氧还蛋白依赖的谷氨酸合酶像那些光养生物。据我们所知，这是第一次在非光合生物中观察到铁氧还蛋白依赖的谷氨酸合酶。从H.嗜热菌是一个单体的168 kDa的多肽同源的铁氧还蛋白依赖性谷氨酸脱氢酶从光养生物。与已知的铁氧还蛋白依赖性谷氨酸脱氢酶相比，H。嗜热菌谷氨酸合酶表现出转氨酶活性。此外，该谷氨酸合酶不与含有[2Fe-2S]簇的植物型铁氧还蛋白（来自该细菌的Fd 3）反应，但与含有[4Fe-4S]簇的细菌铁氧还蛋白（来自该细菌的Fd 1和Fd 2）反应。有趣的是，H.嗜热菌谷氨酸合酶被还原性三羧酸循环（该生物体的中心碳代谢途径）中的一些有机酸激活。这种类型的激活还没有任何其他谷氨酸脱氢酶的报道，这种性质可能使控制氮同化的碳代谢。
Glutamate synthases are classified according to their specificities for electron donors. Ferredoxin-dependent glutamate synthases had been found only in plants and cyanobacteria, whereas many bacteria have NADPH-dependent glutamate synthases. In this study, Hydrogenobacter thermophilus, a hydrogen-oxidizing chemoautotrophic bacterium, was shown to possess a ferredoxin-dependent glutamate synthase like those of phototrophs. This is the first observation, to our knowledge, of a ferredoxin-dependent glutamate synthase in a nonphotosynthetic organism. The purified enzyme from H. thermophilus was shown to be a monomer of a 168-kDa polypeptide homologous to ferredoxin-dependent glutamate synthases from phototrophs. In contrast to known ferredoxin-dependent glutamate synthases, the H. thermophilus glutamate synthase exhibited glutaminase activity. Furthermore, this glutamate synthase did not react with a plant-type ferredoxin (Fd3 from this bacterium) containing a [2Fe-2S] cluster but did react with bacterial ferredoxins (Fd1 and Fd2 from this bacterium) containing [4Fe-4S] clusters. Interestingly, the H. thermophilus glutamate synthase was activated by some of the organic acids in the reductive tricarboxylic acid cycle, the central carbon metabolic pathway of this organism. This type of activation has not been reported for any other glutamate synthases, and this property may enable the control of nitrogen assimilation by carbon metabolism.