Chromatin compaction by human MeCP2 - Assembly of novel secondary chromatin structures in the absence of DNA methylation
Chromatin compaction by human MeCP2 - Assembly of novel secondary chromatin structures in the absence of DNA methylation
复制标题
DOI：
10.1074/jbc.m305308200
复制
发表时间：
2003-08-22
影响因子：
4.8
通讯作者：
Hansen, JC
中科院分区：
文献类型：
--
作者：
Georgel, PT;Horowitz-Scherer, RA;Hansen, JC
甲基化CpG结合蛋白2（MeCP2）是一种转录抑制因子，它包含一个N端甲基化DNA结合结构域、一个中央转录调控结构域以及一个功能未知的C端结构域。虽然当前的MeCP2功能模型提出组蛋白去乙酰化酶在基因组特定甲基化区域的局部募集，但尚不清楚MeCP2是否需要DNA甲基化才能与染色质结合，以及在没有其他蛋白质的情况下MeCP2的结合是否会影响染色质结构。为了解决这些问题，我们对MeCP2与生化定义的核小体阵列之间形成的复合物进行了表征。在接近1个MeCP2/核小体的摩尔比时，未甲基化的核小体阵列既形成了广泛浓缩的椭球形颗粒，也形成了寡聚的超结构。此外，与所有其他已知的染色质浓缩蛋白明显不同的是，MeCP2介导的染色质压缩在没有一价或二价阳离子的情况下也能发生。对特定错义及无义MeCP2突变体的分析表明，染色质浓缩能力存在于该蛋白除甲基化DNA结合结构域之外的区域。这些数据表明，MeCP2能组装不依赖于DNA修饰的新型二级染色质结构，并提示MeCP2使染色质沉默的能力可能部分与其对大规模染色质组织的影响有关。
MeCP2 is a transcriptional repressor that contains an N-terminal methylated DNA-binding domain, a central transcription regulation domain, and a C-terminal domain of unknown function. Whereas current models of MeCP2 function evoke localized recruitment of histone deacetylases to specific methylated regions of the genome, it is unclear whether MeCP2 requires DNA methylation to bind to chromatin or whether MeCP2 binding influences chromatin structure in the absence of other proteins. To address these issues, we have characterized the complexes formed between MeCP2 and biochemically defined nucleosomal arrays. At molar ratios near 1 MeCP2/nucleosome, unmethylated nucleosomal arrays formed both extensively condensed ellipsoidal particles and oligomeric suprastructures. Furthermore, MeCP2-mediated chromatin compaction occurred in the absence of monovalent or divalent cations, in distinct contrast to all other known chromatin-condensing proteins. Analysis of specific missense and nonsense MeCP2 mutants indicated that the ability to condense chromatin resides in region(s) of the protein other than the methylated DNA-binding domain. These data demonstrate that MeCP2 assembles novel secondary chromatin structures independent of DNA modification and suggest that the ability of MeCP2 to silence chromatin may be related in part to its effects on large-scale chromatin organization.