title: Structural basis for the Smad5 MH1 domain to recognize different DNA sequences.
abstract: Smad proteins are important intracellular mediators of TGF-β signalling, which transmit signals directly from cell surface receptors to the nucleus. The MH1 domain of Smad plays a key role in DNA recognition. Two types of DNA sequence were identified as Smad binding motifs: the Smad binding element (SBE) and the GC-rich sequence. Here we report the first crystal structure of the Smad5 MH1 domain in complex with the GC-rich sequence. Compared with the Smad5-MH1/SBE complex structure, the Smad5 MH1 domain contacts the GC-rich site with the same β-hairpin, but the detailed interaction modes are different. Conserved β-hairpin residues make base specific contacts with the minimal GC-rich site, 5'-GGC-3'. The assembly of Smad5-MH1 on the GC-rich DNA also results in distinct DNA conformational changes. Moreover, the crystal structure of Smad5-MH1 in complex with a composite DNA sequence demonstrates that the MH1 domain is targeted to each binding site (GC-rich or SBE) with modular binding modes, and the length of the DNA spacer affects the MH1 assembly. In conclusion, our work provides the structural basis for the recognition and binding specificity of the Smad MH1 domain with the DNA targets.
authors: MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Nan
authors: N
authors: Chai
authors: Department of Otolaryngology Head and Neck Surgery, Institute of Otolaryngology, Chinese PLA General Hospital, Beijing 100853, China.
authors: Wan-Xin
authors: WX
authors: Li
authors: MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Jue
authors: J
authors: Wang
authors: MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors: Zhi-Xin
authors: ZX
authors: Wang
authors: Department of Otolaryngology Head and Neck Surgery, Institute of Otolaryngology, Chinese PLA General Hospital, Beijing 100853, China yangsm301@263.net.
authors: Shi-Ming
authors: SM
authors: Yang
authors: MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing 100084, China jiaweiwu@mail.tsinghua.edu.cn.
authors: Jia-Wei
authors: JW
authors: Wu
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D020862:GC Rich Sequence; D055029:Inverted Repeat Sequences; D051379:Mice; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051900:Smad3 Protein / Q000378:metabolism; D051902:Smad5 Protein / Q000737:chemistry* / Q000378:metabolism
chemical_list: C497790:SMAD3 protein, human; D051900:Smad3 Protein; D051902:Smad5 Protein; C497798:Smad5 protein, mouse; D004247:DNA