Darnell Jennifer C, Fraser Claire E, Mostovetsky Olga, Darnell Robert B
Laboratory of Molecular Neuro-oncology, The Rockefeller University, New York, NY 10065, USA.
Hum Mol Genet. 2009 Sep 1;18(17):3164-77. doi: 10.1093/hmg/ddp255. Epub 2009 Jun 1.
Fragile X mental retardation is caused by loss-of-function of a single gene encoding FMRP, an RNA-binding protein that harbors three canonical RNA-binding domains, two KH-type and one RGG box. Two autosomal paralogs of FMRP, FXR1P and FXR2P, are similar to FMRP in their overall structure, including the presence of putative RNA-binding domains, but to what extent they provide functional redundancy with FMRP is unclear. Although FMRP has been characterized as a polyribosome-associated regulator of translation, less is known about the functions of FXR1P and FXR2P. For example, FMRP binds intramolecular G-quadruplex and kissing complex RNA (kcRNA) ligands via the RGG box and KH2 domain, respectively, although the RNA ligands of FXR1P and FXR2P are unknown. Here we demonstrate that FXR1P and FXR2P KH2 domains bind kcRNA ligands with the same affinity as the FMRP KH2 domain although other KH domains do not. RNA ligand recognition by this family is highly conserved, as the KH2 domain of the single Drosophila ortholog, dFMRP, also binds kcRNA. kcRNA was able to displace FXR1P and FXR2P from polyribosomes as it does for FMRP, and this displacement was FMRP-independent. This suggests that all three family members recognize the same binding site on RNA mediating their polyribosome association, and that they may be functionally redundant with regard to this aspect of translational control. In contrast, FMRP is unique in its ability to recognize G-quadruplexes, suggesting the FMRP RGG domain may play a non-redundant role in the pathophysiology of the disease.
脆性X智力障碍是由编码FMRP的单个基因功能丧失引起的，FMRP是一种RNA结合蛋白，含有三个典型的RNA结合结构域，两个KH型和一个RGG框。FMRP的两个常染色体旁系同源物FXR1P和FXR2P在整体结构上与FMRP相似，包括存在假定的RNA结合结构域，但它们在多大程度上与FMRP提供功能冗余尚不清楚。尽管FMRP已被表征为多核糖体相关的翻译调节因子，但对FXR1P和FXR2P的功能了解较少。例如，FMRP分别通过RGG框和KH2结构域结合分子内G-四链体和亲吻复合体RNA（kcRNA）配体，尽管FXR1P和FXR2P的RNA配体尚不清楚。在这里，我们证明FXR1P和FXR2P的KH2结构域与FMRP的KH2结构域以相同的亲和力结合kcRNA配体，尽管其他KH结构域不结合。该家族对RNA配体的识别高度保守，因为果蝇单个直系同源物dFMRP的KH2结构域也结合kcRNA。kcRNA能够像对FMRP一样将FXR1P和FXR2P从多核糖体上置换下来，并且这种置换不依赖于FMRP。这表明所有三个家族成员都识别RNA上介导其多核糖体结合的相同结合位点，并且它们在翻译控制的这一方面可能具有功能冗余。相比之下，FMRP在识别G-四链体的能力方面是独特的，这表明FMRP的RGG结构域可能在该疾病的病理生理学中发挥非冗余作用。
