Proton-Coupled Electron Transfer with Biomimetic Models of the [2Fe-2S] Rieske Cl

描述(申请人提供)：铁硫团簇被认为是典型的电子转移辅助因素，但在一些系统中有越来越多的证据表明，这种团簇经历了质子耦合电子转移(PCET)。例如，在线粒体中，几个[2Fe-2S]簇介导PCET反应，包括参与ATP合成的Rieske簇和帮助调节这一过程的mitoNEET簇。这两个集群都促进了PCET，这里建议进行模型研究，以发展对这些过程的详细了解。作为Bc1复合体Q循环的一部分，Rieske簇参与了对苯二酚的氧化还原循环，这一过程需要严格的调控，以避免形成最终导致氧化应激和组织损伤的半喹酮中间体。MitoNEET蛋白已被确定为用于治疗2型糖尿病的噻唑烷二酮(TZD)家族药物的靶点，该蛋白是SRWHQWLDO WDUJHW IRU$O]KHLPHU6V 3DUNLQVRQ6V DQG VWURNH GUXJV了解这些和相关的簇如何介导PCET是理解其生物学功能的关键，并可能为新的治疗奠定基础。由于生物系统的复杂性，这种理解最好是用特征良好的模型系统来发展。拟议的实验研究的目标是：i)制备和研究作为Rieske和MitoNEET团簇模型的合成[2Fe-2S]团簇的PCET反应性，以及ii)确定影响PCET进出[Fe-S]团簇的速率和机制的因素。仿生的[2Fe-2S]团簇将在生物相关的氧化态FeIII/III和FeII/III以及质子化和去质子化状态下制备。这些同系物将通过各种技术进行彻底表征，包括核磁共振、IR、EPR和UV-Vis光谱、SQUID磁测量和X射线结晶学。还将测量这些团簇的热化学性质--它们的氧化还原电位和pKa值1。然后将进行PCET和ET反应的动力学和机理研究，重点是与生物相关的反应。结合所有这些不同的测量将导致对这种团簇的PCET反应性的详细描述，例如，包括两个铁中心之间的磁耦合程度如何影响PCET。然后将这些体系与其他不含咪唑或咪唑配体的模型[Fe-S]体系进行比较。这些同系物的质子化很可能发生在硫原子上，这有助于理解质子化的位置如何影响[Fe-S]团簇的PCET。总而言之，这些研究将提供[Fe-S]团簇上PCET的基本描述，这些研究的结果可能为上述疾病提供见解。此外，这些结果将指导未来以[Fe-S]团簇为特征的酶的机制建议，并将促进我们对硫和多金属位置上的PCET的理解，这两种位置都普遍存在于生物系统中。 与公共健康相关：拟议的研究将提供仿生[2Fe-2S]团簇中质子耦合电子转移(PCET)反应的基本描述。几种含有[2FE-2S]簇的蛋白质介导PCET，簇中的故障与许多疾病有关，包括线粒体肌病和Wolfram综合征2。此外，其中一些蛋白质是KHLPHU6V 3DUNLQVRQ6V中风和2型糖尿病治疗的潜在靶点。

DESCRIPTION (provided by applicant): Iron sulfur clusters are viewed as the prototypical electron transfer cofactors, but there is increasing evidence in a number of systems that such clusters undergo proton-coupled electron transfer (PCET). In the mitochondria, for instance, several [2Fe-2S] clusters mediate PCET reactions, including Rieske clusters, which are involved with ATP synthesis, and mitoNEET clusters, which help regulate this process. Both of these clusters facilitate PCET, and proposed here are model studies to develop a detailed understanding of such processes. As part of the Q-cycle of the bc1 complex, Rieske clusters are involved in the redox cycling of quinones, a process that requires tight regulation to avoid formation of semiquinone intermediates which ultimately leads to oxidative stress and tissue damage. The mitoNEET protein has been identified as the target of the thiazolidinedione (TZD) family of drugs, which are used to treat type 2 diabetes, and this protein is a SRWHQWLDO WDUJHW IRU $O]KHLPHU6V 3DUNLQVRQ6V DQG VWURNH GUXJV Knowledge of how these and related clusters mediate PCET is key to understanding their biological function and could lay the foundation for new treatments. Owing to the complexity of the biological systems, this understanding is best developed with well- characterized model systems. The goals of the proposed experimental studies are: i) to prepare and study the PCET reactivity of synthetic [2Fe-2S] clusters that are models for Rieske and mitoNEET clusters, and ii) to establish factors that affect the rate and mechanism of PCET to/from [Fe-S] clusters. Biomimetic [2Fe-2S] clusters will be prepared in both biologically relevant oxidation states, FeIII/III and FeII/III, and in both their protonated and deprotonated states. These congeners will be thoroughly characterized by a variety of techniques, including NMR, IR, EPR, and UV-vis spectroscopy, SQUID magnetometry, and x-ray crystallography. The thermochemical properties of these clusters - their redox potentials and pKa values 1 will also be measured. Kinetic and mechanistic studies of PCET and ET reactions will then be undertaken, with an emphasis on biologically relevant reactions. Combining all these various measurements will lead to a detailed description of the PCET reactivity of such clusters, including, for example, how the extent of magnetic coupling between the two iron centers affects PCET. These systems will then be compared with other model [Fe-S] systems that do not contain an imidazole or imidazolate ligand. Protonation of these congeners will likely occur at the sulfur, providing an understanding of how the site of protonation affects PCET at [Fe-S] clusters. Collectively, these studies will provide a fundamental description of PCET at [Fe-S] clusters, and the results of these studies may provide insights to the above-mentioned diseases. Additionally, these results will guide future mechanistic proposals for enzymes that feature [Fe-S] clusters, and will further our understanding of PCET at sulfur and at multi-metallic sites, both of which are prevalent in biological systems. PUBLIC HEALTH RELEVANCE: The proposed research will provide a fundamental description of the proton-coupled electron transfer (PCET) reactions at biomimetic [2Fe-2S] clusters. Several proteins that incorporate [2Fe-2S] clusters mediate PCET, and malfunctions in the clusters have been associated with numerous diseases including mitochondrial myopathies and Wolfram Syndrome 2. Moreover, some of these proteins are potential targets for $O]KHLPHU6V 3DUNLQVRQ6V stroke, and type 2 diabetes therapeutics.