From the MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
From the MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
J Biol Chem. 2018 Jun 15;293(24):9210-9222. doi: 10.1074/jbc.RA118.002291. Epub 2018 Apr 25.
Mmi1 is an essential RNA-binding protein in the fission yeast that eliminates meiotic transcripts during normal vegetative growth. Mmi1 contains a YTH domain that binds specific RNA sequences, targeting mRNAs for degradation. The YTH domain of Mmi1 uses a noncanonical RNA-binding surface that includes contacts outside the conserved fold. Here, we report that an N-terminal extension that is proximal to the YTH domain enhances RNA binding. Using X-ray crystallography, NMR, and biophysical methods, we show that this low-complexity region becomes more ordered upon RNA binding. This enhances the affinity of the interaction of the Mmi1 YTH domain with specific RNAs by reducing the dissociation rate of the Mmi1-RNA complex. We propose that the low-complexity region influences RNA binding indirectly by reducing dynamic motions of the RNA-binding groove and stabilizing a conformation of the YTH domain that binds to RNA with high affinity. Taken together, our work reveals how a low-complexity region proximal to a conserved folded domain can adopt an ordered structure to aid nucleic acid binding.
Mmi1 是裂殖酵母中一种必需的 RNA 结合蛋白，它在正常的营养生长过程中消除减数分裂转录本。Mmi1 含有一个 YTH 结构域，该结构域可以结合特定的 RNA 序列，从而靶向 mRNAs 进行降解。Mmi1 的 YTH 结构域使用非典型的 RNA 结合表面，包括保守折叠之外的接触。在这里，我们报告说，靠近 YTH 结构域的 N 端延伸增强了 RNA 结合。我们使用 X 射线晶体学、NMR 和生物物理方法表明，该低复杂度区域在 RNA 结合时变得更加有序。这通过降低 Mmi1-RNA 复合物的解离速率，增强了 Mmi1 YTH 结构域与特定 RNA 相互作用的亲和力。我们提出，低复杂度区域通过降低 RNA 结合槽的动态运动并稳定与 RNA 高亲和力结合的 YTH 结构域的构象，间接地影响 RNA 结合。总之，我们的工作揭示了靠近保守折叠结构域的低复杂度区域如何采用有序结构来辅助核酸结合。
