Crystal structure of CO-bound cytochrome c oxidase determined by serial femtosecond X-ray crystallography at room temperature
Crystal structure of CO-bound cytochrome c oxidase determined by serial femtosecond X-ray crystallography at room temperature
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DOI：
10.1073/pnas.1705628114
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发表时间：
2017-07-25
影响因子：
11.1
通讯作者：
Rousseau, Denis L.
中科院分区：
文献类型：
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作者：
Ishigami, Izumi;Zatsepin, Nadia A.;Rousseau, Denis L.
细胞色素c氧化酶（CcO）是电子传递链中的末端酶，通过利用氧还原为水所产生的自由能使质子跨线粒体内膜易位。已经提出了几种氧化还原耦合质子易位机制，但它们缺乏确认，部分原因是由于强烈的同步辐射引起的辐射损伤伪影而缺乏可靠的结构信息。在这里，我们报告的室温，中性pH值（6.8），在一氧化碳（CO）结合态的牛CcO（bCcO）的无损伤结构，在2.3埃的分辨率，通过连续飞秒X射线晶体学（SFX）与X射线自由电子激光获得。作为比较，从在同步加速器光源处收集的数据获得了分辨率为1.95埃的等效结构。在SFX结构中，CO与血红素a（3）铁原子配位，具有类似于142度的弯曲Fe-C-O角。相比之下，在同步加速器结构中，Fe-CO键断裂; CO重新定位到Cu-B附近的新位置，这反过来又向血红素a（3）铁移动了大约0.38埃。结构比较显示，配体与SFX结构中的血红素a（3）铁结合与变构结构转变相关，涉及血红素a和a（3）之间的螺旋-X的部分解旋，从而在两个血红素基团之间建立通信连接，为随后的氧化还原化学过程中的质子易位奠定基础。
Cytochrome c oxidase (CcO), the terminal enzyme in the electron transfer chain, translocates protons across the inner mitochondrial membrane by harnessing the free energy generated by the reduction of oxygen to water. Several redox-coupled proton translocation mechanisms have been proposed, but they lack confirmation, in part from the absence of reliable structural information due to radiation damage artifacts caused by the intense synchrotron radiation. Here we report the room temperature, neutral pH (6.8), damage-free structure of bovine CcO (bCcO) in the carbon monoxide (CO)-bound state at a resolution of 2.3 angstrom, obtained by serial femtosecond X-ray crystallography (SFX) with an X-ray free electron laser. As a comparison, an equivalent structure was obtained at a resolution of 1.95 angstrom, from data collected at a synchrotron light source. In the SFX structure, the CO is coordinated to the heme a(3) iron atom, with a bent Fe-C-O angle of similar to 142 degrees. In contrast, in the synchrotron structure, the Fe-CO bond is cleaved; CO relocates to a new site near Cu-B, which, in turn, moves closer to the heme a(3) iron by similar to 0.38 angstrom. Structural comparison reveals that ligand binding to the heme a(3) iron in the SFX structure is associated with an allosteric structural transition, involving partial unwinding of the helix-X between heme a and a(3), thereby establishing a communication linkage between the two heme groups, setting the stage for proton translocation during the ensuing redox chemistry.