Protein radicals in O2 reduction by Cytochrome Oxidase

描述（由申请人提供）：将研究金属酶细胞色素c氧化酶的作用机制。细胞色素氧化酶通过在双核血红素a3/CuB活性位点催化氧还原成水来维持电子流通过呼吸酶级联。细胞色素氧化酶利用在此过程中释放的能量，并利用它进行质子的跨膜泵送，从而直接有助于化学渗透质子梯度的建立。细胞色素氧化酶最近加入了一类新的金属自由基酶，其独特的组氨酸-酪氨酸交联位点被氧化成自由基。作为配体的CuB的自由基网站的结构位置强烈表明其在分子氧还原和质子泵的作用。由于活性位点的结构，自由基物种既没有直接观察到，也没有使用传统的光谱技术进行表征。我们打算克服这一限制，使用两个新的和独特的仪器，桥接三个光谱域-电子吸收，红外振动和电子顺磁-从而显着提高分辨率和灵敏度。我们最近的研究结果表明，芳香族自由基可以检测和其特征在于，即使在大的蛋白质的紫外吸收。使用新的方法，我们将调查的关键模型自由基，即酪氨酸，色氨酸，组氨酸和模型的组氨酸-酪氨酸网站，重点是他们的紫外吸收和振动特性。研究结果将应用于细胞色素氧化酶中难识别自由基的检测。质子化状态的自由基网站在催化循环的关键阶段将特别调查，因为质子在能量守恒的细胞色素氧化酶中发挥的核心作用。本提案中描述的技术和预期结果将直接适用于广泛的医学相关酶。应用紫外光谱法进行自由基检测将为快速增长的金属自由基酶家族中瞬态自由基的早期检测和动力学研究提供一种简单易行的工具。

DESCRIPTION (provided by applicant): The mechanism by which metalloenzyme cytochrome c oxidase operates will be studied. Cytochrome oxidase sustains electron flow through a cascade of respiratory enzymes in mitochondrion by catalyzing reduction of oxygen into water at the binuclear heme a3/CuB active site. Cytochrome oxidase harnesses the energy released in this process and utilizes it for transmembrane pumping of protons thus directly contributing to the buildup of chemiosmotic proton gradient. Cytochrome oxidase recently joined a new class of metalloradical enzymes.The unique histidine-tyrosine cross-linked site is oxidized to a radical. Structural position of the radical site as a ligand to CuB strongly suggests its role in both the dioxygen reduction and proton pumping. Due to the structure of the active site, radical species have neither been directly observed nor characterized using traditional spectroscopic techniques. We intend to overcome this limitation by using two new and unique instruments, which bridge three spectroscopic domains - electronic absorption, infra-red vibrational and electron paramagnetic - thus dramatically improving resolution and sensitivity. Our recent results show that aromatic radicals can be detected and characterized by their UV absorption even in large proteins. Using new methodology we will investigate key models radicals, namely tyrosine, tryptophan, histidine and the model for histidine-tyrosine site, with the emphasis on their UV absorption and vibrational properties. The results will be applied to detection of elusive radicals in cytochrome oxidase. Protonation states of radical sites at critical stages of the catalytic cycle will be particularly investigated because of the central role protons play in energy conservation by cytochrome oxidase. The techniques described in this proposal and anticipated results will be directly applicable for a broad range of medically relevant enzymes. Application of UV spectroscopy for radical detection will provide a simple and accessible tool for an early detection and kinetic studies of transient radicals in the rapidly growing family of metalloradical enzymes.