Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529, ROC.
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529, ROC; Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan 11529, ROC; Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu, Taiwan 30013, ROC.
Structure. 2017 Mar 7;25(3):469-481. doi: 10.1016/j.str.2017.01.012. Epub 2017 Feb 23.
CshA is a dimeric DEAD-box helicase that cooperates with ribonucleases for mRNA turnover. The molecular mechanism for how a dimeric DEAD-box helicase aids in RNA decay remains unknown. Here, we report the crystal structure and small-angle X-ray scattering solution structure of the CshA from Geobacillus stearothermophilus. In contrast to typical monomeric DEAD-box helicases, CshA is exclusively a dimeric protein with the RecA-like domains of each protomer forming a V-shaped structure. We show that the C-terminal domains protruding outward from the tip of the V-shaped structure is critical for mediating strong RNA binding and is crucial for efficient RNA-dependent ATP hydrolysis. We also show that RNA remains bound with CshA during ATP hydrolysis cycles and thus bulk RNAs could be unwound and degraded in a processive manner through cooperation between exoribonucleases and CshA. A dimeric helicase is hence preserved in RNA-degrading machinery for efficient RNA turnover in prokaryotes and eukaryotes.
CshA 是一种二聚体 DEAD 盒解旋酶，与核糖核酸酶一起参与 mRNA 周转。二聚体 DEAD 盒解旋酶如何帮助 RNA 降解的分子机制尚不清楚。在这里，我们报告了来自嗜热脂肪芽孢杆菌的 CshA 的晶体结构和小角度 X 射线散射溶液结构。与典型的单体 DEAD 盒解旋酶不同，CshA 仅为二聚体蛋白，每个单体的 RecA 样结构域形成 V 形结构。我们表明，从 V 形结构尖端向外突出的 C 端结构域对于介导强 RNA 结合至关重要，对于有效进行 RNA 依赖性 ATP 水解至关重要。我们还表明，在 ATP 水解循环过程中 RNA 仍与 CshA 结合，因此通过外切核糖核酸酶和 CshA 之间的合作，可以以连续的方式解开和降解大量 RNA。因此，在原核生物和真核生物中，二聚体解旋酶在 RNA 降解机制中得以保留，以实现高效的 RNA 周转。
