Chua Gabriella N L, Watters John W, Olinares Paul Dominic B, Luo Joshua A, Chait Brian T, Liu Shixin
Laboratory of Nanoscale Biophysics and Biochemistry, The Rockefeller University, New York, NY, USA.
Tri-Institutional PhD Program in Chemical Biology, New York, NY, USA.
bioRxiv. 2023 Jun 5:2023.06.02.543478. doi: 10.1101/2023.06.02.543478.
Methyl-CpG-binding protein 2 (MeCP2) is an essential chromatin-binding protein whose mutations cause Rett syndrome (RTT), a leading cause of monogenic intellectual disabilities in females. Despite its significant biomedical relevance, the mechanism by which MeCP2 navigates the chromatin epigenetic landscape to regulate chromatin structure and gene expression remains unclear. Here, we used correlative single-molecule fluorescence and force microscopy to directly visualize the distribution and dynamics of MeCP2 on a variety of DNA and chromatin substrates. We found that MeCP2 exhibits differential diffusion dynamics when bound to unmethylated and methylated bare DNA. Moreover, we discovered that MeCP2 preferentially binds nucleosomes within the context of chromatinized DNA and stabilizes them from mechanical perturbation. The distinct behaviors of MeCP2 at bare DNA and nucleosomes also specify its ability to recruit TBLR1, a core component of the NCoR1/2 co-repressor complex. We further examined several RTT mutations and found that they disrupt different aspects of the MeCP2-chromatin interaction, rationalizing the heterogeneous nature of the disease. Our work reveals the biophysical basis for MeCP2's methylation-dependent activities and suggests a nucleosome-centric model for its genomic distribution and gene repressive functions. These insights provide a framework for delineating the multifaceted functions of MeCP2 and aid in our understanding of the molecular mechanisms of RTT.
甲基-CpG结合蛋白2（MeCP2）是一种重要的染色质结合蛋白，其突变会导致雷特综合征（RTT），这是女性单基因智力残疾的主要原因。尽管其具有重要的生物医学相关性，但MeCP2在染色质表观遗传景观中调控染色质结构和基因表达的机制仍不清楚。在这里，我们使用相关单分子荧光和力显微镜直接观察MeCP2在各种DNA和染色质底物上的分布和动态。我们发现，当与未甲基化和甲基化的裸DNA结合时，MeCP2表现出不同的扩散动力学。此外，我们发现MeCP2在染色质化DNA的背景下优先结合核小体，并使其免受机械扰动的影响。MeCP2在裸DNA和核小体上的不同行为也决定了其招募TBLR1的能力，TBLR1是NCoR1/2共抑制复合物的核心成分。我们进一步研究了几种RTT突变，发现它们破坏了MeCP2-染色质相互作用的不同方面，从而解释了该疾病的异质性。我们的工作揭示了MeCP2甲基化依赖性活动的生物物理基础，并提出了一个以核小体为中心的模型来解释其基因组分布和基因抑制功能。这些见解为描绘MeCP2的多方面功能提供了一个框架，并有助于我们理解RTT的分子机制。
