Bole Medhavi, Menon Lakshmi, Mihailescu Mihaela-Rita
Department of Chemistry & Biochemistry, Duquesne University, Pittsburgh, PA 15282, USA.
Mol Biosyst. 2008 Dec;4(12):1212-9. doi: 10.1039/b812537f. Epub 2008 Oct 27.
Fragile X syndrome, the most common form of inherited mental retardation is caused by the expansion of a CGG trinucleotide repeat in the fragile X mental retardation 1 (fmr1) gene. The abnormal expansion of the CGG repeat causes hypermethylation and subsequent silencing of the fmr1 gene, resulting in the loss of the fragile X mental retardation protein (FMRP). FMRP has been shown to use its arginine-glycine-glycine rich region (RGG box) to bind to messenger RNAs that form G quadruplex structures. Several studies reported that the G quadruplex RNA recognition alone is not sufficient for FMRP RGG box binding and that an additional stem and/or a G quadruplex-stem junction region may also be important in recognition. In this study we have used biophysical methods such as fluorescence, UV, CD and NMR spectroscopy to demonstrate that the recognition of the RNA G quadruplex structure per se, in the absence of a stem region, is sufficient for the FMRP high affinity and specific binding. These findings indicate that the presence of a stem structure in some of the FMRP G quadruplex forming mRNAs is not a requirement for protein recognition as previously believed, but rather for the proper formation of the correct RNA G quadruplex structure recognized by FMRP.
脆性X综合征是遗传性智力障碍最常见的形式，由脆性X智力障碍1（fmr1）基因中的CGG三核苷酸重复序列扩增引起。CGG重复序列的异常扩增导致fmr1基因的高甲基化及随后的沉默，导致脆性X智力障碍蛋白（FMRP）缺失。已证明FMRP利用其富含精氨酸-甘氨酸-甘氨酸的区域（RGG框）与形成G-四链体结构的信使RNA结合。多项研究报告称，仅G-四链体RNA识别不足以实现FMRP RGG框结合，额外的茎和/或G-四链体-茎连接区域在识别中可能也很重要。在本研究中，我们使用了荧光、紫外、圆二色和核磁共振光谱等生物物理方法来证明，在没有茎区域的情况下，对RNA G-四链体结构本身的识别足以实现FMRP的高亲和力和特异性结合。这些发现表明，在一些形成FMRP G-四链体的mRNA中，茎结构的存在并非如先前认为的那样是蛋白质识别的必要条件，而是为了正确形成被FMRP识别的正确RNA G-四链体结构。
