Anosova Irina, Melnik Svitlana, Tripsianes Konstantinos, Kateb Fatiha, Grummt Ingrid, Sattler Michael
Institute of Structural Biology, Helmholtz Zentrum München, Neuherberg D-85764, Germany Biomolecular NMR and Center for Integrated Protein Science Munich (CIPSM), Department Chemie, Technische Universität München, Garching D-85747, Germany.
Division of Molecular Biology of the Cell II, DKFZ-ZMBH Alliance, German Cancer Research Center, Heidelberg D-69120, Germany.
Nucleic Acids Res. 2015 May 26;43(10):5208-20. doi: 10.1093/nar/gkv365. Epub 2015 Apr 27.
The chromatin remodeling complex NoRC, comprising the subunits SNF2h and TIP5/BAZ2A, mediates heterochromatin formation at major clusters of repetitive elements, including rRNA genes, centromeres and telomeres. Association with chromatin requires the interaction of the TAM (TIP5/ARBP/MBD) domain of TIP5 with noncoding RNA, which targets NoRC to specific genomic loci. Here, we show that the NMR structure of the TAM domain of TIP5 resembles the fold of the MBD domain, found in methyl-CpG binding proteins. However, the TAM domain exhibits an extended MBD fold with unique C-terminal extensions that constitute a novel surface for RNA binding. Mutation of critical amino acids within this surface abolishes RNA binding in vitro and in vivo. Our results explain the distinct binding specificities of TAM and MBD domains to RNA and methylated DNA, respectively, and reveal structural features for the interaction of NoRC with non-coding RNA.
染色质重塑复合物NoRC由亚基SNF2h和TIP5/BAZ2A组成，介导包括rRNA基因、着丝粒和端粒在内的主要重复元件簇处的异染色质形成。与染色质的结合需要TIP5的TAM（TIP5/ARBP/MBD）结构域与非编码RNA相互作用，该非编码RNA将NoRC靶向特定的基因组位点。在这里，我们表明TIP5的TAM结构域的NMR结构类似于在甲基-CpG结合蛋白中发现的MBD结构域的折叠。然而，TAM结构域表现出扩展的MBD折叠，具有独特的C末端延伸，构成了一个新的RNA结合表面。该表面内关键氨基酸的突变在体外和体内消除了RNA结合。我们的结果分别解释了TAM和MBD结构域对RNA和甲基化DNA的不同结合特异性，并揭示了NoRC与非编码RNA相互作用的结构特征。
