Nishikawa T, Nagadoi A, Yoshimura S, Aimoto S, Nishimura Y
Graduate School of Integrated Science, Yokohama City University, Japan.
Structure. 1998 Aug 15;6(8):1057-65. doi: 10.1016/s0969-2126(98)00106-3.
Mammalian telomeres consist of long tandem arrays of the double-stranded TTAGGG sequence motif packaged by a telomere repeat binding factor, TRF1. The DNA-binding domain of TRF1 shows sequence homology to each of three tandem repeats of the DNA-binding domain of the transcriptional activator c-Myb. The isolated c-Myb-like domain of human TRF1 (hTRF1) binds specifically to telomeric DNA as a monomer, in a similar manner to that of homeodomains. So far, the only three-dimensional structure of a telomeric protein to be determined is that of a yeast telomeric protein, Rap 1p. The DNA-binding domain of Rap 1p contains two subdomains that are structurally closely related to c-Myb repeats. We set out to determine the solution structure of the DNA-binding domain of hTRF1 in order to establish its mode of DNA binding.
The solution structure of the DNA-binding domain of hTRF1 has been determined and shown to comprise three helices. The architecture of the three helices is very similar to that of each Rap 1p subdomain and also to that of each c-Myb repeat. The second and third helix form a helix-turn-helix (HTH) variant. The length of the third helix of hTRF1 is similar to that of the second subdomain of Rap 1p.
The hTRF1 DNA-binding domain is likely to bind to DNA in a similar manner to that of the second subdomain of Rap 1p. On the basis of the Rap 1p-DNA complex, a model of the hTRF1 DNA-binding domain in complex with human telomeric DNA was constructed. In addition to DNA recognition by the HTH variant, a flexible N-terminal arm of hTRF1 is likely to interact with DNA.
哺乳动物端粒由双链 TTAGGG 序列基序的长串联阵列组成，这些序列由端粒重复结合因子 TRF1 包装。TRF1 的 DNA 结合结构域与转录激活因子 c-Myb 的 DNA 结合结构域的三个串联重复序列中的每一个都显示出序列同源性。人 TRF1（hTRF1）分离出的 c-Myb 样结构域以单体形式特异性结合端粒 DNA，其方式与同源结构域相似。到目前为止，唯一已确定三维结构的端粒蛋白是酵母端粒蛋白 Rap 1p。Rap 1p 的 DNA 结合结构域包含两个亚结构域，它们在结构上与 c-Myb 重复序列密切相关。我们着手确定 hTRF1 的 DNA 结合结构域的溶液结构，以建立其 DNA 结合模式。
已确定 hTRF1 的 DNA 结合结构域的溶液结构，显示其由三个螺旋组成。这三个螺旋的结构与每个 Rap 1p 亚结构域以及每个 c-Myb 重复序列的结构非常相似。第二和第三个螺旋形成一种螺旋-转角-螺旋（HTH）变体。hTRF1 第三个螺旋的长度与 Rap 1p 第二个亚结构域的长度相似。
hTRF1 的 DNA 结合结构域可能以与 Rap 1p 第二个亚结构域相似的方式结合 DNA。基于 Rap 1p-DNA 复合物，构建了 hTRF1 的 DNA 结合结构域与人类端粒 DNA 复合物的模型。除了通过 HTH 变体识别 DNA 外，hTRF1 的柔性 N 末端臂可能与 DNA 相互作用。
