Department of Biochemistry, Ludwig-Maximilians-Universität München, Munich, Germany.
Gene Center, Ludwig-Maximilians-Universität München, Munich, Germany.
Nat Struct Mol Biol. 2018 Sep;25(9):823-832. doi: 10.1038/s41594-018-0115-8. Epub 2018 Sep 3.
Nuclear actin (N-actin) and actin-related proteins (Arps) are critical components of several chromatin modulating complexes, including the chromatin remodeler INO80, but their function is largely elusive. Here, we report the crystal structure of the 180-kDa Arp8 module of Saccharomyces cerevisiae INO80 and establish its role in recognition of extranucleosomal linker DNA. Arp8 engages N-actin in a manner distinct from that of other actin-fold proteins and thereby specifies recruitment of the Arp4-N-actin heterodimer to a segmented scaffold of the helicase-SANT-associated (HSA) domain of Ino80. The helical HSA domain spans over 120 Å and provides an extended binding platform for extranucleosomal entry DNA that is required for nucleosome sliding and genome-wide nucleosome positioning. Together with the recent cryo-electron microscopy structure of INO80-nucleosome complex, our findings suggest an allosteric mechanism by which INO80 senses 40-bp linker DNA to conduct highly processive chromatin remodeling.
核肌动蛋白（N-actin）和肌动蛋白相关蛋白（Arps）是几种染色质调节复合物的关键组成部分，包括染色质重塑酶 INO80，但它们的功能在很大程度上尚不清楚。在这里，我们报告了酿酒酵母 INO80 的 180kDa Arp8 模块的晶体结构，并确定了其在识别额外核小体连接 DNA 中的作用。Arp8 以与其他肌动蛋白折叠蛋白不同的方式与 N-actin 结合，从而特异性地将 Arp4-N-actin 异二聚体招募到 Ino80 的螺旋酶-SANT 相关（HSA）结构域的分段支架上。螺旋 HSA 结构域跨越超过 120Å，并为额外核小体进入 DNA 提供了一个扩展的结合平台，这对于核小体滑动和全基因组核小体定位是必需的。结合最近的 INO80-核小体复合物的冷冻电子显微镜结构，我们的发现表明了一种变构机制，INO80 通过该机制感知 40bp 的连接 DNA 来进行高度连续的染色质重塑。
