Structure-function relations in Rieske-type proteins

铁硫蛋白在自然界中无处不在，并出现在大多数代谢途径中，对决定其物理化学性质的参数的理解是生物化学的核心问题。其中最有趣的是具有两个半胱氨酸和两个组氨酸的铁配位的2Fe-2S簇。其中包括bc1（及其相关）复合物中的Rieske铁硫蛋白（ISP），以及本项目拟研究的几种Rieske型细菌蛋白，包括Sulfolobus sp.菌株7的古细菌硫氧还蛋白（SDX）和S. solfaricus的Rieske型铁氧还蛋白（ARF）。这些蛋白质的一个显著特征是氧化还原电位的广泛变化，从-100到300 mV，由2Fe-2S簇显示，尽管它们的连接相似。最近的晶体学结构表明，在这一范围的两个极端，蛋白质簇结合域的配体取向相似。这意味着每个特定簇的氧化还原电位和原生水解性质是由蛋白质环境的其他独特特征控制的。为了了解蛋白质的功能，必须在原子水平上确定影响这些参数的因素。我们建议利用先进的磁共振技术来研究上述三种rieske型簇的蛋白质环境，重点是利用二维ESEEM来探索顺磁中心与邻近核自旋之间的相互作用。我们将对数据进行分析，以提供结构信息，并将其与ISP和萘- 1,2-双加氧酶的晶体结构进行比较。光谱结果将为精确测定组氨酸和半胱氨酸配体的配位、氢键和非配位氮的存在以及溶剂的可及性提供约束。通过对由分子工程产生的突变菌株进行类似的实验，我们预计我们将能够识别控制簇的氧化还原和原解特性的蛋白质环境的局部特征，它们在反应机制中的作用，以及在不同菌株中产生功能修饰的变化。这些结果将回答有关rieske型蛋白氧化还原电位控制的结构因素的一些基本问题，并为其他氧化还原蛋白的类似问题提供见解。

Iron-sulfur proteins are ubiquitous in nature and occur in most metabolic pathways, and an understanding of the parameters determining their physico-chemical properties is a central problem of biochemistry. Among the most interesting are the 2Fe-2S clusters that have as a common feature the liganding of the irons by two cysteines and two histidines. These include the Rieske iron-sulfur protein (ISP) of the bc1 (and related) complexes, and several Rieske-type bacterial proteins, including the archaeal sulredoxin (SDX) of Sulfolobus sp. Strain 7 and Rieske-type ferredoxin (ARF) from S. solfaricus to be investigated in this project. A remarkable feature of these proteins is the wide variation in redox potentials, from -100 to 300 mV, exhibited by the 2Fe-2S clusters, despite their similar ligation. Recent crystallographic structures show a similar orientation of ligands in the cluster binding domain in proteins at both extremes of this range. This implies that the redox potentials and protolytic properties of each particular cluster are controlled by other unique features of the protein environment. To understand how the proteins function, the factors influencing these parameters must be determined at the atomic level for each protein. We propose to investigate the protein environment of the three Rieske-type clusters above by using advanced magnetic resonance techniques, with an emphasis on 2-D ESEEM to explore the interaction between the paramagnetic centers and nuclear spins in the neighborhood. We will analyze the data so as to provide structural information, and compared this with the crystallographic structured of ISP, and of naphthalene- 1,2-dioxygenase. The spectroscopic results will provide constraints to allow precise determination of the cluster environment including coordination of histidine and cysteine ligands, presence of hydrogen bonds and non-coordinated nitrogens, and accessibility of solvent. By performing similar experiments with mutant strains generated by molecular engineering, we anticipate that we will be able to identify the local features of the protein environment that control the redox and protolytic properties of the clusters, their role in reaction mechanisms, and the changes that produce functional modification in different strains. The results will answer some fundamental questions about structural factors controlling the redox potentials of Rieske-type proteins, and provide insights to similar questions in other redox proteins.