Elucidating Fragile X Syndrome by Investigating FMRP Molecular Function

脆性X综合征（FXS）是智力障碍的最常见遗传原因， 孤独症的单基因病因患有这种疾病的个体，约4000名男孩中有1名，约7000名女孩中有1名， 有一系列的症状，包括语言和发育迟缓，侵略性，过度兴奋， 固执这种疾病是三联核苷酸重复扩增和表观遗传沉默的结果， FMR 1基因。Fmr 1敲除（KO）小鼠显示出与该综合征相关的病理生理学， 作为治疗开发的模型。许多早期治疗集中在下游的失调事件， FMRP的活性，但很少集中在FMRP功能本身的分子机制。FMRP结合特异性 它主要通过与编码区的相互作用来完成。这一观察加上 它通常抑制翻译的事实导致了这样的假设，即它通常会使核糖体停滞或减慢 易位，从而减少多肽延伸。几项研究表明，FMRP确实会停滞 核糖体上的特定mRNA。新出现的证据表明，FMRP结合核糖体，但分子 平移失速的机制仍然是一个谜。高分辨率的结构分析可能表明 在与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， 首先鉴定mRNA中被FMRP停滞的核糖体结合的区域，然后使用这样的RNA区域， 形成FMRP停滞的核糖体复合物用于冷冻-EM结构测定。FMRP-核糖体接触 点不仅表明核糖体停滞的分子机制，而且表明潜在的 可以模拟FMRP功能以减轻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.