Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL) Heidelberg, 69117 Heidelberg, Germany.
Biomedical Center and Center for Integrated Protein Science, Ludwig-Maximilians-University, 82152 Martinsried, Germany.
Nucleic Acids Res. 2019 May 7;47(8):4319-4333. doi: 10.1093/nar/gkz125.
Maleless (MLE) is an evolutionary conserved member of the DExH family of helicases in Drosophila. Besides its function in RNA editing and presumably siRNA processing, MLE is best known for its role in remodelling non-coding roX RNA in the context of X chromosome dosage compensation in male flies. MLE and its human orthologue, DHX9 contain two tandem double-stranded RNA binding domains (dsRBDs) located at the N-terminal region. The two dsRBDs are essential for localization of MLE at the X-territory and it is presumed that this involves binding roX secondary structures. However, for dsRBD1 roX RNA binding has so far not been described. Here, we determined the solution NMR structure of dsRBD1 and dsRBD2 of MLE in tandem and investigated its role in double-stranded RNA (dsRNA) binding. Our NMR and SAXS data show that both dsRBDs act as independent structural modules in solution and are canonical, non-sequence-specific dsRBDs featuring non-canonical KKxAXK RNA binding motifs. NMR titrations combined with filter binding experiments and isothermal titration calorimetry (ITC) document the contribution of dsRBD1 to dsRNA binding in vitro. Curiously, dsRBD1 mutants in which dsRNA binding in vitro is strongly compromised do not affect roX2 RNA binding and MLE localization in cells. These data suggest alternative functions for dsRBD1 in vivo.
MLE 是果蝇 DExH 家族解旋酶中进化保守的成员。除了在 RNA 编辑和推测的 siRNA 加工中的功能外,MLE 最著名的作用是在雄性果蝇的 X 染色体剂量补偿中重塑非编码 roX RNA。MLE 和其人类同源物 DHX9 包含两个串联的双链 RNA 结合结构域(dsRBD)位于 N 端区域。这两个 dsRBD 对于 MLE 在 X 区的定位是必不可少的,据推测这涉及到 roX 二级结构的结合。然而,到目前为止,还没有描述 dsRBD1 与 roX RNA 的结合。在这里,我们确定了 MLE 的串联 dsRBD1 和 dsRBD2 的溶液 NMR 结构,并研究了其在双链 RNA(dsRNA)结合中的作用。我们的 NMR 和 SAXS 数据表明,两个 dsRBD 都作为独立的结构模块在溶液中起作用,是规范的、非序列特异性的 dsRBD,具有非典型的 KKxAXK RNA 结合基序。NMR 滴定实验结合过滤结合实验和等温滴定量热法(ITC)记录了 dsRBD1 在体外对 dsRNA 结合的贡献。奇怪的是,dsRBD1 突变体在体外强烈削弱 dsRNA 结合的突变体不影响 roX2 RNA 结合和 MLE 在细胞中的定位。这些数据表明 dsRBD1 在体内具有替代功能。