Reversible sequestration of active site cysteines in a 2Fe-2S-bridged dimer provides a mechanism for glutaredoxin 2 regulation in human mitochondria
Reversible sequestration of active site cysteines in a 2Fe-2S-bridged dimer provides a mechanism for glutaredoxin 2 regulation in human mitochondria
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DOI：
10.1074/jbc.m608179200
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发表时间：
2007-02-02
影响因子：
4.8
通讯作者：
Oppermann, Udo
中科院分区：
文献类型：
--
作者：
Johansson, Catrine;Kavanagh, Kathryn L.;Oppermann, Udo
人线粒体谷氧还蛋白2(GLRX2)控制细胞内氧化还原平衡和细胞凋亡，处于酶活性单体和静止二聚体的动态平衡状态。人GLRX2的单体和二聚体的晶体结构都显示出明显的谷胱甘肽结合模式，并显示出2Fe-2S桥联的二聚体。铁-硫簇通过N-末端活性中心半胱氨酸、半胱氨酸-37和还原型谷胱甘肽进行配位。这些结构表明，高GSH/GSSG比值可以通过形成2Fe-2S桥联的二聚体来锁定N端的活性部位半胱氨酸，或者通过非共价结合和阻断单体中的活性部位来抑制该酶。允许GLRX2而不是其他谷氧还蛋白形成含铁硫二聚体的性质可能是由于活性中心基序中的脯氨酸到丝氨酸的取代，使得主链在这一区域具有更大的灵活性，并提供了与稳定的谷胱甘肽的极性相互作用。这似乎是铁-硫簇的一种新用途，其中簇的结合通过隔离活性位点残基来使蛋白质失活，并且通过亚细胞氧化还原状态的改变而失去簇产生催化活性蛋白质。在氧化条件下，二聚体很容易分离成无铁的活性单体，为氧化应激下谷氧还蛋白的激活提供了结构上的解释。
Human mitochondrial glutaredoxin 2 (GLRX2), which controls intracellular redox balance and apoptosis, exists in a dynamic equilibrium of enzymatically active monomers and quiescent dimers. Crystal structures of both monomeric and dimeric forms of human GLRX2 reveal a distinct glutathione binding mode and show a 2Fe-2S-bridged dimer. The iron-sulfur cluster is coordinated through the N-terminal active site cysteine, Cys-37, and reduced glutathione. The structures indicate that the enzyme can be inhibited by a high GSH/GSSG ratio either by forming a 2Fe-2S-bridged dimer that locks away the N-terminal active site cysteine or by binding non-covalently and blocking the active site as seen in the monomer. The properties that permit GLRX2, and not other glutaredoxins, to form an iron-sulfur-containing dimer are likely due to the proline-to-serine substitution in the active site motif, allowing the main chain more flexibility in this area and providing polar interaction with the stabilizing glutathione. This appears to be a novel use of an iron-sulfur cluster in which binding of the cluster inactivates the protein by sequestering active site residues and where loss of the cluster through changes in subcellular redox status creates a catalytically active protein. Under oxidizing conditions, the dimers would readily separate into iron-free active monomers, providing a structural explanation for glutaredoxin activation under oxidative stress.