Leschziner Andres E, Saha Anjanabha, Wittmeyer Jacqueline, Zhang Yongli, Bustamante Carlos, Cairns Bradley R, Nogales Eva
Department of Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2007 Mar 20;104(12):4913-8. doi: 10.1073/pnas.0700706104. Epub 2007 Mar 13.
Chromatin remodeling complexes (remodelers) are large, multisubunit macromolecular assemblies that use ATP hydrolysis to alter the structure and positioning of nucleosomes. The mechanisms proposed for remodeler action on nucleosomes are diverse, and require structural evaluation and insights. Previous reconstructions of remodelers using electron microscopy revealed interesting features, but also significant discrepancies, prompting new approaches. Here, we use the orthogonal tilt reconstruction method, which is well suited for heterogeneous samples, to provide a reconstruction of the yeast RSC (remodel the structure of chromatin) complex. Two interesting features are revealed: first, we observe a deep central cavity within RSC, displaying a remarkable surface complementarity for the nucleosome. Second, we are able to visualize two distinct RSC conformers, revealing a major conformational change in a large protein "arm," which may shift to further envelop the nucleosome. We present a model of the RSC-nucleosome complex that rationalizes the single molecule results obtained by using optical tweezers and also discuss the mechanistic implications of our structures.
染色质重塑复合物（重塑因子）是大型多亚基大分子组装体，利用ATP水解来改变核小体的结构和定位。针对重塑因子作用于核小体所提出的机制多种多样，需要进行结构评估和深入了解。此前利用电子显微镜对重塑因子进行的重建揭示了有趣的特征，但也存在显著差异，这促使人们采用新的方法。在这里，我们使用非常适合异质样品的正交倾斜重建方法，来对酵母RSC（重塑染色质结构）复合物进行重建。揭示了两个有趣的特征：第一，我们在RSC中观察到一个深的中央腔，它对核小体表现出显著的表面互补性。第二，我们能够可视化两种不同的RSC构象，揭示了一个大的蛋白质“臂”中的主要构象变化，该“臂”可能会进一步移动以包裹核小体。我们提出了一个RSC-核小体复合物模型，该模型使通过光镊获得的单分子结果合理化，并讨论了我们结构的机制意义。
