The crystal structure of a reduced [NiFeSe] hydrogenase provides an image of the activated catalytic center
The crystal structure of a reduced [NiFeSe] hydrogenase provides an image of the activated catalytic center
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DOI：
10.1016/s0969-2126(99)80072-0
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发表时间：
1999-05-01
期刊：
影响因子：
--
通讯作者：
Fontecilla-Camps, JC
中科院分区：
文献类型：
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作者：
Garcin, E;Vernede, X;Fontecilla-Camps, JC
背景：[NiFeSe]氢化酶是催化h - 2H(+)+2e（-）反应的金属酶。它们通常是异二聚体，在它们的小亚基中含有三个铁硫簇，在它们的大亚基中含有一个含镍铁的活性位点，其中包括一个硒代半胱氨酸（SeCys）配体。结果：我们在这里报道了在2.15埃分辨率下，从杆状脱硫菌中提取的质周[NiFeSe]氢化酶的还原活性形式的x射线结构。氧化后制备的脱硫弧菌和还原后的杆状霉加氢酶的活性位点比较表明，还原后的酶的镍-铁距离比氧化后的酶短0.4埃。此外，在制备的D. gigas酶中检测到的假定的氧配体在D. baculatum氢化酶中不存在。我们还观察到活性位点镍硒半胱氨酸配体和相邻的Glu18残基的温度因子都高于平均水平，这表明这两个部分都参与了活性位点和分子表面之间的质子转移。[NiFeSe]和[NiFe]氢化酶之间的其他区别是存在第三个[4Fe4S]簇取代在D. gigas酶中发现的[3Fe4S]簇，并且在两个[NiFe]氢化酶的大亚基的C端已经描述了一个假定的铁中心取代镁离子。结论：氢分子的异裂可能是由镍中心和硒代半胱氨酸残基介导的。除了修饰酶的催化性能外，硒配体还可以保护镍原子不被氧化。我们得出结论，假定的氧配体是非活性的“未准备”[NiFe]氢化酶的标志。
Background: [NiFeSe] hydrogenases are metalloenzymes that catalyze the reaction H-2 2H(+)+2e(-). They are generally heterodimeric, contain three iron-sulfur clusters in their small subunit and a nickel-iron-containing active site in their large subunit that includes a selenocysteine (SeCys) ligand.Results: We report here the X-ray structure at 2.15 Angstrom resolution of the periplasmic [NiFeSe] hydrogenase from Desulfomicrobium baculatum in its reduced, active form. A comparison of active sites of the oxidized, as-prepared, Desulfovibrio gigas and the reduced D. baculatum hydrogenases shows that in the reduced enzyme the nickel-iron distance is 0.4 Angstrom shorter than in the oxidized enzyme. In addition, the putative oxo ligand, detected in the as prepared D. gigas enzyme, is absent from the D. baculatum hydrogenase. We also observe higher-than-average temperature factors for both the active site nickel-selenocystein ligand and the neighboring Glu18 residue, suggesting that both these moieties are involved in proton transfer between the active site and the molecular surface. Other differences between [NiFeSe] and [NiFe] hydrogenases are the presence of a third [4Fe4S] cluster replacing the [3Fe4S] cluster found in the D. gigas enzyme, and a putative iron center that substitutes the magnesium ion that has already been described at the C terminus of the large subunit of two [Nife] hydrogenases.Conclusions: The heterolytic cleavage of molecular hydrogen seems to be mediated by the nickel center and the selenocysteine residue. Beside modifying the catalytic properties of the enzyme, the selenium ligand might protect the nickel atom from oxidation. We conclude that the putative oxo ligand is a signature of inactive 'unready' [NiFe] hydrogenases.