Homodimeric MyoD preferentially binds tetraplex structures of regulatory sequences of muscle-specific genes
Homodimeric MyoD preferentially binds tetraplex structures of regulatory sequences of muscle-specific genes
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DOI：
10.1074/jbc.m500820200
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发表时间：
2005-07-22
影响因子：
4.8
通讯作者：
Fry, M
中科院分区：
文献类型：
--
作者：
Etzioni, S;Yafe, A;Fry, M
通过碱性螺旋-环-螺旋蛋白MyoD和E12或E47的异二聚体与肌肉特异性基因的启动子或增强子区域中的共有E盒序列d（CANNTG）结合来激活肌原性转录。MyoD的同源二聚体与E盒的结合不太紧密，是效率较低的转录激活剂。我们实验室的最新结果（Yafe，A.，Etzioni，S.，Weisman-Shomer，P.，Fry，M.（2005）Nucleic Acids Res.33，2887-2900）表明，几种肌肉特异性基因的调节序列含有不成比例的高含量的鸟嘌呤簇，其容易形成发夹和平行链的单分子和双分子四链体结构。在这里，我们已经表明，全长重组MyoD的同源二聚体形成复合物与肌肉特异性调控序列的双分子四链体结构，但不与它们的双链，发夹，或单分子四链体形式。MyoD-四链体DNA复合物的解离常数Kd低18.7-39.9倍，反映了同源二聚体MyoD与双分子四链体DNA结构的优先结合超过E-box DNA。相反，MyoD-E47异二聚体与E-box形成更紧密的复合物，如其相对于具有双分子四链体DNA结构的复合物低6.8-19.0倍的K-d所示。类似地，MyoD的60个氨基酸的碱性螺旋-环-螺旋结构域的同源二聚体比全长MyoD的同源二聚体更有效地结合E盒，而四链体DNA的效率较低。可能是MyoD同二聚体与四链体DNA结构的有利结合降低了它们激活肌肉特异性基因转录的能力，而MyoD-E47异二聚体的形成及其与E-box DNA的优先结合增强了转录。
Myogenic transcription is activated by the binding of heterodimers of the basic helix-loop-helix proteins MyoD and E12 or E47 to a consensus E-box sequence, d(CANNTG), in promoter or enhancer regions of muscle-specific genes. Homodimers of MyoD bind E-box less tightly and are less efficient activators of transcription. Recent results from our laboratory (Yafe, A., Etzioni, S., Weisman-Shomer, P., and Fry, M. ( 2005) Nucleic Acids Res. 33, 2887-2900) indicate that regulatory sequences of several muscle-specific genes contain a disproportionate high content of guanine clusters that readily form hairpin and parallel-stranded unimolecular and bimolecular tetraplex structures. Here we have shown that homodimers of full-length recombinant MyoD formed complexes with bimolecular tetraplex structures of muscle-specific regulatory sequences but not with their double-stranded, hairpin, or unimolecular tetraplex forms. Preferential binding of homodimeric MyoD to bimolecular tetraplex DNA structures over E-box DNA was reflected by the 18.7-39.9-fold lower dissociation constants, K-d, of the MyoD-tetraplex DNA complexes. Conversely, MyoD-E47 heterodimers formed tighter complexes with E-box as indicated by their 6.8-19.0-fold lower K-d relative to complexes with bimolecular tetraplex DNA structures. Similarly, homodimers of the 60-amino acid basic helix-loop-helix domain of MyoD bound E-box more efficiently and tetraplex DNA less efficiently than homodimers of full-length MyoD. It might be that the favored binding of MyoD homodimers to tetraplex DNA structures lowers their ability to activate muscle-specific gene transcription, whereas the formation of MyoD-E47 heterodimers and their preferential binding to E-box DNA enhance transcription.