Adén Jörgen, Wallgren Marcus, Storm Patrik, Weise Christoph F, Christiansen Alexander, Schröder Wolfgang P, Funk Christiane, Wolf-Watz Magnus
Department of Chemistry, Umea University, Umea, Sweden.
Biochim Biophys Acta. 2011 Dec;1814(12):1880-90. doi: 10.1016/j.bbapap.2011.07.011. Epub 2011 Jul 21.
Peroxiredoxin Q (PrxQ) isolated from Arabidopsis thaliana belongs to a family of redox enzymes called peroxiredoxins, which are thioredoxin- or glutaredoxin-dependent peroxidases acting to reduce peroxides and in particular hydrogen peroxide. PrxQ cycles between an active reduced state and an inactive oxidized state during its catalytic cycle. The catalytic mechanism involves a nucleophilic attack of the catalytic cysteine on hydrogen peroxide to generate a sulfonic acid intermediate with a concerted release of a water molecule. This intermediate is subsequently relaxed by the reaction of a second cysteine, denoted the resolving cysteine, generating an intramolecular disulfide bond and release of a second water molecule. PrxQ is recycled to the active state by a thioredoxin-dependent reduction. Previous structural studies of PrxQ homologues have provided the structural basis for the switch between reduced and oxidized conformations. Here, we have performed a detailed study of the activity, structure and dynamics of PrxQ in both the oxidized and reduced states. Reliable and experimentally validated structural models of PrxQ in both oxidation states were generated using homology based modeling. Analysis of NMR spin relaxation rates shows that PrxQ is monomeric in both oxidized and reduced states. As evident from R(2) relaxation rates the reduced form of PrxQ undergoes unprecedented dynamics on the slow μs-ms timescale. The ground state of this conformational dynamics is likely the stably folded reduced state as implied by circular dichroism spectroscopy. We speculate that the extensive dynamics is intimately related to the catalytic function of PrxQ.
从拟南芥中分离出的过氧化物酶Q（PrxQ）属于一类名为过氧化物酶的氧化还原酶家族，它们是依赖硫氧还蛋白或谷氧还蛋白的过氧化物酶，作用是还原过氧化物，尤其是过氧化氢。PrxQ在其催化循环中在活性还原态和非活性氧化态之间循环。催化机制涉及催化半胱氨酸对过氧化氢的亲核攻击，以生成磺酸中间体并协同释放一个水分子。随后，第二个半胱氨酸（称为解离半胱氨酸）的反应使该中间体松弛，生成分子内二硫键并释放第二个水分子。PrxQ通过硫氧还蛋白依赖性还原循环回到活性状态。先前对PrxQ同源物的结构研究为还原态和氧化态构象之间的转换提供了结构基础。在这里，我们对氧化态和还原态的PrxQ的活性、结构和动力学进行了详细研究。使用基于同源性的建模生成了氧化态和还原态PrxQ的可靠且经过实验验证的结构模型。核磁共振自旋弛豫率分析表明，PrxQ在氧化态和还原态均为单体。从R(2)弛豫率可以明显看出，还原态的PrxQ在慢微秒-毫秒时间尺度上经历了前所未有的动力学变化。圆二色光谱表明，这种构象动力学的基态可能是稳定折叠的还原态。我们推测这种广泛的动力学与PrxQ的催化功能密切相关。
