Qiu Yupeng, Niu Hengyao, Vukovic Lela, Sung Patrick, Myong Sua
Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA.
Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, PO Box 208024, New Haven, CT 06520, USA.
Structure. 2015 Jun 2;23(6):1018-27. doi: 10.1016/j.str.2015.04.006. Epub 2015 May 21.
Trinucleotide repeat (TNR) expansion is the root cause for many known congenital neurological and muscular disorders in human including Huntington's disease, fragile X syndrome, and Friedreich's ataxia. The stable secondary hairpin structures formed by TNR may trigger fork stalling during replication, causing DNA polymerase slippage and TNR expansion. Srs2 and Sgs1 are two helicases in yeast that resolve TNR hairpins during DNA replication and prevent genome expansion. Using single-molecule fluorescence, we investigated the unwinding mechanism by which Srs2 and Sgs1 resolves TNR hairpin and compared it with unwinding of duplex DNA. While Sgs1 unwinds both structures indiscriminately, Srs2 displays repetitive unfolding of TNR hairpin without fully unwinding it. Such activity of Srs2 shows dependence on the folding strength and the total length of TNR hairpin. Our results reveal a disparate molecular mechanism of Srs2 and Sgs1 that may contribute differently to efficient resolving of the TNR hairpin.
三核苷酸重复序列(TNR)扩增是人类许多已知先天性神经和肌肉疾病的根本原因,包括亨廷顿舞蹈症、脆性X综合征和弗里德赖希共济失调。TNR形成的稳定二级发夹结构可能在复制过程中引发叉停滞,导致DNA聚合酶滑动和TNR扩增。Srs2和Sgs1是酵母中的两种解旋酶,它们在DNA复制过程中解开TNR发夹并防止基因组扩增。利用单分子荧光技术,我们研究了Srs2和Sgs1解开TNR发夹的机制,并将其与双链DNA的解旋进行了比较。虽然Sgs1不加区分地解开这两种结构,但Srs2对TNR发夹进行重复展开而不完全解开它。Srs2的这种活性显示出对TNR发夹折叠强度和总长度的依赖性。我们的结果揭示了Srs2和Sgs1不同的分子机制,它们可能对有效解开TNR发夹有不同的贡献。