Structural insight into maintenance methylation by mouse DNA methyltransferase 1 (Dnmt1)
Structural insight into maintenance methylation by mouse DNA methyltransferase 1 (Dnmt1)
复制标题
DOI：
10.1073/pnas.1019629108
复制
发表时间：
2011-05-31
影响因子：
11.1
通讯作者：
Tajima, Shoji
中科院分区：
文献类型：
--
作者：
Takeshita, Kohei;Suetake, Isao;Tajima, Shoji
DNA 中胞嘧啶的甲基化通过可遗传的基因沉默在发育中发挥着至关重要的作用。 DNA 甲基转移酶 Dnmt1 通过优先甲基化基因组中的半甲基化 CpG 位点，负责将甲基化模式传播到下一代。然而，Dnmt1 如何维持甲基化模式尚不完全清楚。在这里，我们报道了小鼠Dnmt1大片段（291-1620）及其与辅因子S-腺苷-L-蛋氨酸及其产物S-腺苷-L-同型半胱氨酸的复合物的晶体结构。值得注意的是，在没有 DNA 的情况下，负责将 Dnmt1 定位到复制焦点的 N 端结构域被插入到 DNA 结合袋中，表明必须除去该结构域才能发生甲基化。在与 S-腺苷-L-甲硫氨酸结合后，催化半胱氨酸残基经历构象转变至催化活性位置。为了识别半甲基化 DNA，Dnmt1 预计将利用悬垂在假定的 DNA 结合口袋上方的目标识别结构域。考虑到最近报道的 Dnmt1 较短片段结构，即 CXXC 基序将自身定位在催化口袋中并防止异常的从头甲基化，我们认为维持甲基化是一个伴随着结构变化的多步骤过程。
Methylation of cytosine in DNA plays a crucial role in development through inheritable gene silencing. The DNA methyltransferase Dnmt1 is responsible for the propagation of methylation patterns to the next generation via its preferential methylation of hemimethylated CpG sites in the genome; however, how Dnmt1 maintains methylation patterns is not fully understood. Here we report the crystal structure of the large fragment (291-1620) of mouse Dnmt1 and its complexes with cofactor S-adenosyl-L-methionine and its product S-adenosyl-L-homocystein. Notably, in the absence of DNA, the N-terminal domain responsible for targeting Dnmt1 to replication foci is inserted into the DNA-binding pocket, indicating that this domain must be removed for methylation to occur. Upon binding of S-adenosyl-L-methionine, the catalytic cysteine residue undergoes a conformation transition to a catalytically competent position. For the recognition of hemimethylated DNA, Dnmt1 is expected to utilize a target recognition domain that overhangs the putative DNA-binding pocket. Taking into considerations the recent report of a shorter fragment structure of Dnmt1 that the CXXC motif positions itself in the catalytic pocket and prevents aberrant de novo methylation, we propose that maintenance methylation is a multistep process accompanied by structural changes.