Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
EMBO J. 2011 Jun 1;30(11):2167-76. doi: 10.1038/emboj.2011.127. Epub 2011 Apr 26.
The p53 tumour suppressor gene, the most frequently mutated gene in human cancer, encodes a transcription factor that contains sequence-specific DNA binding and homo-tetramerization domains. Interestingly, the affinities of p53 for specific and non-specific DNA sites differ by only one order of magnitude, making it hard to understand how this protein recognizes its specific DNA targets in vivo. We describe here the structure of a p53 polypeptide containing both the DNA binding and oligomerization domains in complex with DNA. The structure reveals that sequence-specific DNA binding proceeds via an induced fit mechanism that involves a conformational switch in loop L1 of the p53 DNA binding domain. Analysis of loop L1 mutants demonstrated that the conformational switch allows DNA binding off-rates to be regulated independently of affinities. These results may explain the universal prevalence of conformational switching in sequence-specific DNA binding proteins and suggest that proteins like p53 rely more on differences in binding off-rates, than on differences in affinities, to recognize their specific DNA sites.
p53 肿瘤抑制基因是人类癌症中最常发生突变的基因，它编码一种转录因子，含有序列特异性 DNA 结合和同源四聚体化结构域。有趣的是，p53 与特定和非特定 DNA 位点的亲和力仅相差一个数量级，这使得很难理解该蛋白如何在体内识别其特定的 DNA 靶标。我们在这里描述了一个包含 DNA 结合和寡聚化结构域的 p53 多肽与 DNA 形成复合物的结构。该结构揭示了序列特异性 DNA 结合是通过诱导契合机制进行的，该机制涉及 p53 DNA 结合结构域中环 L1 的构象转换。对环 L1 突变体的分析表明，构象转换允许 DNA 结合的离解速率独立于亲和力进行调节。这些结果可能解释了序列特异性 DNA 结合蛋白中普遍存在的构象转换，并表明像 p53 这样的蛋白更多地依赖于结合离解速率的差异，而不是亲和力的差异，来识别其特定的 DNA 位点。
