Telomeres are protein-DNA elements that are located at the ends of linear eukaryotic chromosomes. In concert with various telomere-binding proteins, they play an essential role in genome stability. We determined the structure of the DNA-binding domain of NgTRF1, a double-stranded telomere-binding protein of tobacco, using multidimensional NMR spectroscopy and X-ray crystallography. The DNA-binding domain of NgTRF1 contained the Myb-like domain and C-terminal Myb-extension that is characteristic of plant double-stranded telomere-binding proteins. It encompassed amino acids 561-681 (NgTRF1561-681), and was composed of 4 α-helices. We also determined the structure of NgTRF1561-681 bound to plant telomeric DNA. We identified several amino acid residues that interacted directly with DNA, and confirmed their role in the binding of NgTRF1 to telomere using site-directed mutagenesis. Based on a structural comparison of the DNA-binding domains of NgTRF1 and human TRF1 (hTRF1), NgTRF1 has both common and unique DNA-binding properties. Interaction of Myb-like domain with telomeric sequences is almost identical in NgTRF1561-681 with the DNA-binding domain of hTRF1. The interaction of Arg-638 with the telomeric DNA, which is unique in NgTRF1561-681, may provide the structural explanation for the specificity of NgTRF1 to the plant telomere sequences, (TTTAGGG)n.
Bibliographical noteFunding Information:
We thank Dr Sun-Sin Cha and Ghyung Hwa Kim for assistance at beamline 6B and 4MX of Pohang Light Source. This work was supported in part by grant from the Korea Research Foundation by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2007-314-C00274 to H.S.C.), the Korea Science and Engineering Foundation Grantz (No R112000078010010 to H.S.C.), the NRL program of MOST NRDP (M1-0203-00-0020 to W.L.), the Korea Science and Engineering Foundation (KOSEF) through the Protein Network Research Center at Yonsei University (R112000078010010), the Plant Diversity Research Center (21st Century Frontier Research Program funded by the Ministry of Science and Technology of the Korean government to W.T.K.) and the Plant Metabolism Research Center at Kyung Hee University (Science Research Center Project No. R11-2000-081 from the Korea Science and Engineering Foundation to W.T.K.). This work was also supported by the Basic Science Research Program (C.C.) from the Ministry of Science and Technology of the Republic of Korea and by the NMR Research Program (Y.H.J.) from the Korea Basic Science Institute. S.-G.K., H.B., J.-S B., W.H. and H.P. were recipients of Brain Korea 21 postdoctoral or graduate student scholarship. Funding to pay the Open Access publication charges for this article was provided by the Protein Network Research Center at Yonsei University.
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