From the Department of Biotechnology, Indian Institute of Technology Hyderabad, Kandi, Telangana State 502285, India.
From the Department of Biotechnology, Indian Institute of Technology Hyderabad, Kandi, Telangana State 502285, India
J Biol Chem. 2017 Nov 17;292(46):18732-18746. doi: 10.1074/jbc.M117.796235. Epub 2017 Sep 18.
GAC repeat expansion from five to seven in the exonic region of the gene for cartilage oligomeric matrix protein (COMP) leads to pseudoachondroplasia, a skeletal abnormality. However, the molecular mechanism by which GAC expansions in the gene lead to skeletal dysplasias is poorly understood. Here we used molecular dynamics simulations, which indicate that an A … A mismatch in a d(GAC)·d(GAC) duplex induces negative supercoiling, leading to a local B-to-Z DNA transition. This transition facilitates the binding of d(GAC)·d(GAC) with the Zα-binding domain of human adenosine deaminase acting on RNA 1 (ADAR1, hZα), as confirmed by CD, NMR, and microscale thermophoresis studies. The CD results indicated that hZα recognizes the zigzag backbone of d(GAC)·d(GAC) at the B-Z junction and subsequently converts it into Z-DNA via the so-called passive mechanism. Molecular dynamics simulations carried out for the modeled hZα-d(GAC)d(GAC) complex confirmed the retention of previously reported important interactions between the two molecules. These findings suggest that hZα binding with the GAC hairpin stem in can lead to a non-genetic, RNA editing-mediated substitution in COMP that may then play a crucial role in the development of pseudoachondroplasia.
GAC 重复扩展从五个到七个在软骨寡聚基质蛋白（COMP）基因的外显子区域导致假性软骨发育不全，这是一种骨骼异常。然而，GAC 在基因中扩展导致骨骼发育不良的分子机制还知之甚少。在这里，我们使用分子动力学模拟，表明在 d(GAC)·d(GAC)双链体中的一个 A…A 错配诱导负超螺旋，导致局部 B 到 Z DNA 转变。这种转变促进了 d(GAC)·d(GAC)与人类腺苷脱氨酶作用于 RNA 1（ADAR1，hZα）的 Zα 结合域的结合，这一点通过 CD、NMR 和微尺度热泳研究得到了证实。CD 结果表明，hZα在 B-Z 连接处识别 d(GAC)·d(GAC)的锯齿状骨架，随后通过所谓的被动机制将其转化为 Z-DNA。对建模的 hZα-d(GAC)d(GAC) 复合物进行的分子动力学模拟证实了两个分子之间保留了先前报道的重要相互作用。这些发现表明，hZα与 中的 GAC 发夹茎结合可能导致 COMP 中的非遗传、RNA 编辑介导的取代，这可能在假性软骨发育不全的发展中发挥关键作用。
