Unusual characteristics of the DNA binding domain of epigenetic regulatory protein MeCP2 determine its binding specificity.
Unusual characteristics of the DNA binding domain of epigenetic regulatory protein MeCP2 determine its binding specificity.
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DOI：
10.1021/bi500424z
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发表时间：
2014-06-03
期刊：
影响因子：
2.9
通讯作者：
Brenowitz M
中科院分区：
文献类型：
--
作者：
Khrapunov S;Warren C;Cheng H;Berko ER;Greally JM;Brenowitz M
蛋白MeCP 2通过结合染色质上的甲基-CpG（mCpG）位点介导表观遗传调控。MeCP 2由六个结构域组成，其中一个是甲基结合结构域（MBD），结合双链体DNA中的mCpG位点。我们表明，生理或更高的盐浓度或非特异性的竞争对手DNA的存在下的溶液条件是必要的MBD区分mCpG CpG CpG具有高特异性。在这些溶液条件下，mCpG的特异性超过CpG>100倍。相比之下，MBD不区分羟甲基-CpG与CpG。MBD在位点特异性DNA结合蛋白中是不寻常的，因为（i）特异性不是由对特异性位点的增强的亲和力赋予的，而是由其对通用DNA的亲和力的抑制赋予的，（ii）其与mCpG的特异性结合是高度静电的，以及（iii）其在DNA结合时吸收并置换单价阳离子。MBD对单链DNA显示出异常高的亲和力，与修饰或序列无关。此外，MBD通过非协同结合途径在DNA上形成离散的二聚体。因为第二单体的亲和力比非特异性结合的亲和力大1个数量级，所以MBD二聚体是独特的分子复合物。这些结果的意义的背景下，神经元的功能和发展和MeCP 2相关的发育障碍，如Rett综合征进行了讨论。
The protein MeCP2 mediates epigenetic regulation by binding methyl-CpG (mCpG) sites on chromatin. MeCP2 consists of six domains of which one, the methyl binding domain (MBD), binds mCpG sites in duplex DNA. We show that solution conditions with physiological or greater salt concentrations or the presence of nonspecific competitor DNA is necessary for the MBD to discriminate mCpG from CpG with high specificity. The specificity for mCpG over CpG is >100-fold under these solution conditions. In contrast, the MBD does not discriminate hydroxymethyl-CpG from CpG. The MBD is unusual among site-specific DNA binding proteins in that (i) specificity is not conferred by the enhanced affinity for the specific site but rather by suppression of its affinity for generic DNA, (ii) its specific binding to mCpG is highly electrostatic, and (iii) it takes up as well as displaces monovalent cations upon DNA binding. The MBD displays an unusually high affinity for single-stranded DNA independent of modification or sequence. In addition, the MBD forms a discrete dimer on DNA via a noncooperative binding pathway. Because the affinity of the second monomer is 1 order of magnitude greater than that of nonspecific binding, the MBD dimer is a unique molecular complex. The significance of these results in the context of neuronal function and development and MeCP2-related developmental disorders such as Rett syndrome is discussed.
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