RanGTP 激活 Importin-9 释放组蛋白 H2A-H2B 的分子基础。
Molecular basis of RanGTP-activated release of Histones H2A-H2B from Importin-9.
机构信息
Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson 75080, USA.
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75390, USA.
出版信息
Structure. 2023 Aug 3;31(8):903-911.e3. doi: 10.1016/j.str.2023.06.001. Epub 2023 Jun 27.
Imp9 is the primary importin for shuttling H2A-H2B from the cytoplasm to the nucleus. It employs an unusual mechanism where the binding of RanGTP is insufficient to release H2A-H2B. The resulting stable RanGTP·Imp9·H2A-H2B complex gains nucleosome assembly activity with H2A-H2B able to be deposited into an assembling nucleosome in vitro. Using hydrogen-deuterium exchange coupled with mass spectrometry (HDX), we show that Imp9 stabilizes H2A-H2B beyond the direct-binding site, like other histone chaperones. HDX also shows that binding of RanGTP releases H2A-H2B contacts at Imp9 HEAT repeats 4-5, but not 18-19. DNA- and histone-binding surfaces of H2A-H2B are exposed in the ternary complex, facilitating nucleosome assembly. We also reveal that RanGTP has a weaker affinity for Imp9 when H2A-H2B is bound. Imp9 thus provides a connection between the nuclear import of H2A-H2B and its deposition into chromatin.
Imp9 是将 H2A-H2B 从细胞质转运到细胞核的主要导入蛋白。它采用了一种不寻常的机制，其中 RanGTP 的结合不足以释放 H2A-H2B。由此产生的稳定的 RanGTP·Imp9·H2A-H2B 复合物具有核小体组装活性，H2A-H2B 能够在体外被沉积到正在组装的核小体中。我们使用氢氘交换结合质谱（HDX）表明，Imp9 稳定 H2A-H2B 的能力超过了直接结合位点，就像其他组蛋白伴侣一样。HDX 还表明，RanGTP 的结合会释放 Imp9 的 HEAT 重复 4-5 处的 H2A-H2B 接触，但不会释放 18-19 处的接触。H2A-H2B 的 DNA 和组蛋白结合表面在三元复合物中暴露出来，促进核小体组装。我们还揭示了当 H2A-H2B 结合时，RanGTP 与 Imp9 的亲和力较弱。因此，Imp9 为 H2A-H2B 的核输入与其在染色质中的沉积之间提供了联系。
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