Elucidating Fragile X Syndrome by Investigating FMRP Molecular Function

脆性X综合征(FXS)是导致智能障碍的最常见和最普遍的遗传性原因 导致自闭症的单基因。患有这种疾病的人，每4000名男孩中有1名，每7000名女孩中有1名在场 有一系列症状，包括言语和发育迟缓，攻击性，过度兴奋，以及 坚持不懈。这种疾病是三重核苷酸重复扩增和表观遗传沉默的结果 FMR1基因。FMR1基因敲除(KO)小鼠表现出与该综合征相关的病理生理，因此 作为治疗发展的典范。许多早期治疗关注于DYS调节的事件下游 FMRP的活性，但很少集中在FMRP功能本身的分子机制上。FMRP绑定特定的 主要通过与编码区的相互作用来实现。这一观察结果加上 它通常会抑制翻译，这一事实导致了一种假设，即它通常会使核糖体停滞或减慢 移位，从而减少多肽的伸长。几项研究现在表明，FMRP确实停滞不前 核糖体位于特定的mRNA上。新的证据表明，FMRP与核糖体结合，但分子 翻译失速的机制仍然是一个谜。高分辨率结构分析可能指示区域 与FMRP相关的核糖体上，可能导致小分子或其他 可用于治疗FXS的替代品。考虑到这一长期目标，我们提出了两个具体目标 首先确定mRNA中与FMRP停滞的核糖体结合的区域，然后使用这些RNA区域来 形成FMRP停滞的核糖体复合体，用于冷冻-EM结构测定。FMRP-核糖体接触 点数不仅表明了核糖体停滞的分子机制，而且还暗示了潜在的 可以模仿FMRP功能以缓解FXS的治疗方法。

Fragile X Syndrome (FXS) is the most common inherited cause of intellectual impairment and most prevalent single gene cause of autism. Individuals afflicted with the disorder, 1 in ~4000 boys and 1 in ~7000 girls, present with a range of symptoms including speech and developmental delays, aggression, hyper-excitability, and perseveration. The disorder is the result of a triplet nucleotide repeat expansion and epigenetic silencing of the gene FMR1. Fmr1 knockout (KO) mice display pathophysiologies associated with the syndrome and thus serve as a model for therapeutic development. Many inchoate therapies focus on dys-regulated events downstream of FMRP activity, but few are concentrated on molecular mechanisms of FMRP function itself. FMRP binds specific mRNAs in the brain and does so primarily through interactions with coding regions. This observation plus the fact that it generally inhibits translation has led to the hypothesis that it normally stalls or slows ribosome translocation, thereby reducing polypeptide elongation. Several studies have now shown that indeed FMRP stalls ribosomes on specific mRNAs. Emerging evidence suggests that FMRP binds the ribosome, but the molecular mechanism of translational stalling remains an enigma. High-resolution structural analysis might indicate regions on the ribosome that are associated with FMRP, possibly leading to the development of small-molecule or other replacements that can be used to treat FXS. With that long-term goal in mind, we propose two specific aims to first identify regions in mRNA that are bound by FMRP-stalled ribosomes, and then to use such RNA regions to form FMRP-stalled ribosome complexes for cryo-EM structure determination. The FMRP-ribosome contact points would not only indicate a molecular mechanism of ribosome stalling, but would suggest potential therapeutic approaches that could mimic FMRP function to mitigate FXS.