Cytochrome c polymerization by successive domain swapping at the C-terminal helix
Cytochrome c polymerization by successive domain swapping at the C-terminal helix
复制标题
DOI：
10.1073/pnas.1001839107
复制
发表时间：
2010-07-20
影响因子：
11.1
通讯作者：
Higuchi, Yoshiki
中科院分区：
文献类型：
--
作者：
Hirota, Shun;Hattori, Yoko;Higuchi, Yoshiki
细胞色素c（cyt c）是一种稳定的蛋白质，以单体状态作为细胞色素c氧化酶的电子供体。当细胞凋亡早期线粒体外膜发生透化时，它也会释放到细胞质中。近半个世纪来，人们已经知道细胞色素c形成聚合物，但聚合机理仍然不清楚。我们发现，细胞色素C形成聚合物的连续域交换，其中的C-末端螺旋从其原来的位置在单体和蛋氨酸血红素协调扰动显着。在二聚体和三聚体细胞色素c的晶体结构中，C-末端螺旋被其他细胞色素c分子的相应结构域取代，Met 80从血红素中解离。基于小角X射线散射测量，二聚体、三聚体和四聚体细胞色素c的溶液结构是线性的，其中通过加入PEG和（NH 4）（2）HPO 4，三聚体线性结构向环状结构转变。高阶寡聚体（类似于40 mer）的吸收光谱和圆二色性光谱与二聚体和三聚体的相似，而与单体的不同。对于二聚体、三聚体和四聚体细胞色素c，估计寡聚体解离成单体的Δ H约为每个原聚体单元-20 kcal/mol，其中Met-血红素配位似乎对Δ H有很大贡献。本研究结果表明，细胞色素c聚合发生连续的结构域交换，这可能是一个共同的机制，蛋白质聚合。
Cytochrome c (cyt c) is a stable protein that functions in a monomeric state as an electron donor for cytochrome c oxidase. It is also released to the cytosol when permeabilization of the mitochondrial outer membrane occurs at the early stage of apoptosis. For nearly half a century, it has been known that cyt c forms polymers, but the polymerization mechanism remains unknown. We found that cyt c forms polymers by successive domain swapping, where the C-terminal helix is displaced from its original position in the monomer and Met-heme coordination is perturbed significantly. In the crystal structures of dimeric and trimeric cyt c, the C-terminal helices are replaced by the corresponding domain of other cyt c molecules and Met80 is dissociated from the heme. The solution structures of dimeric, trimeric, and tetrameric cyt c were linear based on small-angle X-ray scattering measurements, where the trimeric linear structure shifted toward the cyclic structure by addition of PEG and (NH4)(2)HPO4. The absorption and CD spectra of high-order oligomers (similar to 40 mer) were similar to those of dimericandtrimeric cyt c but different from those of monomeric cyt c. For dimeric, trimeric, and tetrameric cyt c, the Delta H of the oligomer dissociation to monomers was estimated to be about -20 kcal/mol per protomer unit, where Met-heme coordination appears to contribute largely to Delta H. The present results suggest that cyt c polymerization occurs by successive domain swapping, which may be a common mechanism of protein polymerization.