Methyl-CpG-binding protein 2 (MeCP2) is an essential chromatin-binding protein whose mutations cause Rett syndrome (RTT), a severe neurological disorder that primarily affects young females. The canonical view of MeCP2 as a DNA methylation-dependent transcriptional repressor has proven insufficient to describe its dynamic interaction with chromatin and multifaceted roles in genome organization and gene expression. Here we used single-molecule correlative force and fluorescence microscopy to directly visualize the dynamics of wild-type and RTT-causing mutant MeCP2 on DNA. We discovered that MeCP2 exhibits distinct one-dimensional diffusion kinetics when bound to unmethylated versus CpG methylated DNA, enabling methylation-specific activities such as co-repressor recruitment. We further found that, on chromatinized DNA, MeCP2 preferentially localizes to nucleosomes and stabilizes them from mechanical perturbation. Our results reveal the multimodal behavior of MeCP2 on chromatin that underlies its DNA methylation- and nucleosome-dependent functions and provide a biophysical framework for dissecting the molecular pathology of RTT mutations.

甲基-CpG 结合蛋白 2 （MeCP2） 是一种必需的染色质结合蛋白，其突变会导致雷特综合征 （RTT），这是一种主要影响年轻女性的严重神经系统疾病。将 MeCP2 视为 DNA 甲基化依赖性转录抑制因子的经典观点已被证明不足以描述其与染色质的动态相互作用以及在基因组组织和基因表达中的多方面作用。在这里，我们使用单分子相关力和荧光显微镜直接可视化 DNA 上野生型和 RTT 诱导突变体 MeCP2 的动力学。我们发现，与 CpG 甲基化 DNA 结合时，MeCP2 表现出不同的一维扩散动力学，从而能够进行甲基化特异性活动，例如共阻遏蛋白募集。我们进一步发现，在染色质化的 DNA 上，MeCP2 优先定位于核小体并稳定它们免受机械扰动。我们的结果揭示了 MeCP2 对染色质的多模式行为，这是其 DNA 甲基化和核小体依赖性功能的基础，并为剖析 RTT 突变的分子病理学提供了生物物理框架。