Bioengineering Department, University of Illinois, Urbana, IL 61801, USA.
Structure. 2012 Nov 7;20(11):1872-80. doi: 10.1016/j.str.2012.08.018. Epub 2012 Sep 13.
Human telomeres possess a single-stranded DNA (ssDNA) overhang of TTAGGG repeats, which can self-fold into a G-quadruplex structure. POT1 binds specifically to the telomeric overhang and partners with TPP1 to regulate telomere lengthening and capping, although the mechanism remains elusive. Here, we show that POT1 binds stably to folded telomeric G-quadruplex DNA in a sequential manner, one oligonucleotide/oligosaccharide binding fold at a time. POT1 binds from 3' to 5', thereby unfolding the G-quadruplex in a stepwise manner. In contrast, the POT1-TPP1 complex induces a continuous folding and unfolding of the G-quadruplex. We demonstrate that POT1-TPP1 slides back and forth on telomeric DNA and also on a mutant telomeric DNA to which POT1 cannot bind alone. The sliding motion is specific to POT1-TPP1, as POT1 and ssDNA binding protein gp32 cannot recapitulate this activity. Our results reveal fundamental molecular steps and dynamics involved in telomere structure regulation.
端粒含有单链 DNA（ssDNA）突出的 TTAGGG 重复序列，它可以自我折叠成 G-四链体结构。POT1 特异性结合端粒突出，并与 TPP1 合作调节端粒延长和加帽，尽管其机制尚不清楚。在这里，我们显示 POT1 以顺序方式稳定地结合折叠的端粒 G-四链体 DNA，一次一个寡核苷酸/寡糖结合折叠。POT1 从 3' 到 5' 结合，从而逐步展开 G-四链体。相比之下，POT1-TPP1 复合物诱导 G-四链体的连续折叠和展开。我们证明 POT1-TPP1 在端粒 DNA 上以及 POT1 单独不能结合的突变型端粒 DNA 上前后滑动。滑动运动是 POT1-TPP1 特有的，因为 POT1 和 ssDNA 结合蛋白 gp32 不能重现这种活性。我们的结果揭示了参与端粒结构调节的基本分子步骤和动力学。
