Chen Dong-Hua, Song Jiu-Li, Chuang David T, Chiu Wah, Ludtke Steven J
National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Structure. 2006 Nov;14(11):1711-22. doi: 10.1016/j.str.2006.09.010.
Electron cryomicroscopy reveals an unprecedented conformation of the single-ring mutant of GroEL (SR398) bound to GroES in the presence of Mg-ATP. This conformation exhibits a considerable expansion of the folding cavity, with approximately 80% more volume than the X-ray structure of the equivalent cis cavity in the GroEL-GroES-(ADP)(7) complex. This expanded conformation can encapsulate an 86 kDa heterodimeric (alphabeta) assembly intermediate of mitochondrial branched-chain alpha-ketoacid dehydrogenase, the largest substrate ever observed to be cis encapsulated. The SR398-GroES-Mg-ATP complex is found to exist as a mixture of standard and expanded conformations, regardless of the absence or presence of the substrate. However, the presence of even a small substrate causes a pronounced bias toward the expanded conformation. Encapsulation of the large assembly intermediate is supported by a series of electron cryomicroscopy studies as well as the protection of both alpha and beta subunits of the substrate from tryptic digestion.
电子冷冻显微镜揭示了在Mg-ATP存在下，与GroES结合的GroEL单环突变体（SR398）的一种前所未有的构象。这种构象显示出折叠腔有相当大的扩张，其体积比GroEL-GroES-(ADP)(7)复合物中同等顺式腔的X射线结构大约多80%。这种扩张的构象可以包裹线粒体支链α-酮酸脱氢酶的一个86 kDa异二聚体（αβ）组装中间体，这是迄今观察到的被顺式包裹的最大底物。发现SR398-GroES-Mg-ATP复合物以标准构象和扩张构象的混合物形式存在，无论底物是否存在。然而，即使存在少量底物也会导致明显偏向于扩张构象。一系列电子冷冻显微镜研究以及底物的α和β亚基免受胰蛋白酶消化的保护，都支持了大型组装中间体的包裹。
