Characterization of a unique [FeS] cluster in the electron transfer chain of the oxygen tolerant [NiFe] hydrogenase from Aquifex aeolicus
Characterization of a unique [FeS] cluster in the electron transfer chain of the oxygen tolerant [NiFe] hydrogenase from Aquifex aeolicus
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DOI：
10.1073/pnas.1100610108
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发表时间：
2011-04-12
影响因子：
11.1
通讯作者：
Lubitz, Wolfgang
中科院分区：
文献类型：
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作者：
Pandelia, Maria-Eirini;Nitschke, Wolfgang;Lubitz, Wolfgang
铁-硫团簇是一种多功能的电子转移辅助因子，广泛存在于氢酶等金属酶中。在Aquifex aeolicus的耐氧氢酶I中，这种电子“线”形成了连接到双血红素Cytb的中继器，后者是将O(2)还原为水的呼吸途径的组成部分。与氧敏感氢酶的氨基酸序列比较表明，三个铁-硫簇的结合基序是保守的，其性质和性质迄今尚不清楚。电子顺磁共振谱显示了复杂的信号，揭示了有趣的特征和自旋耦合模式；通过氧化还原滴定，鉴定出三个铁硫团簇处于其通常的氧化还原状态，一个[3Fe4S]和两个[4Fe4S]，但也发现了一个独特的高电势(HP)状态。根据~(57)Fe穆斯堡尔谱，我们认为这种HP型是由于[NiFe]位附近的[4Fe4S]中心处于超氧化状态。该簇的独特环境以剩余的半胱氨酸配位为特征，能够调节氧化还原电位，使其符合[4Fe4S](3+)状态。这实际上是生物[4Fe4S]中心的第一个例子，它在非常小的电势范围内在3+，2+和1+氧化状态之间进行生理切换。我们认为，(1+/2+)氧化还原对服务于经典的电子转移反应，而过氧化步骤与对抗氧化应激的氧化还原开关有关。
Iron-sulfur clusters are versatile electron transfer cofactors, ubiquitous in metalloenzymes such as hydrogenases. In the oxygen-tolerant Hydrogenase I from Aquifex aeolicus such electron "wires" form a relay to a diheme cytb, an integral part of a respiration pathway for the reduction of O(2) to water. Amino acid sequence comparison with oxygen-sensitive hydrogenases showed conserved binding motifs for three iron-sulfur clusters, the nature and properties of which were unknown so far. Electron paramagnetic resonance spectra exhibited complex signals that disclose interesting features and spin-coupling patterns; by redox titrations three iron-sulfur clusters were identified in their usual redox states, a [3Fe4S] and two [4Fe4S], but also a unique high-potential (HP) state was found. On the basis of (57)Fe Mossbauer spectroscopy we attribute this HP form to a superoxidized state of the [4Fe4S] center proximal to the [NiFe] site. The unique environment of this cluster, characterized by a surplus cysteine coordination, is able to tune the redox potentials and make it compliant with the [4Fe4S](3+) state. It is actually the first example of a biological [4Fe4S] center that physiologically switches between 3+, 2+, and 1+ oxidation states within a very small potential range. We suggest that the (1+ /2+) redox couple serves the classical electron transfer reaction, whereas the superoxidation step is associated with a redox switch against oxidative stress.