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Structural Basis for the Identification of an i-Motif Tetraplex Core with a Parallel-Duplex Junction as a Structural Motif in CCG Triplet Repeats

By Yi-Wen Chen, Cyong-Ru Jhan, Stephen Neidle and Ming-Hon Hou


CCG triplet repeats can fold into tetraplex structures, which are associated with the expansion of (CCG)n trinucleotide sequences in certain neurological diseases. These structures are stabilized by intertwining i-motifs. However, the structural basis for tetraplex i-motif formation in CCG triplet repeats remains largely unknown. We report the first crystal structure of a CCG-repeat sequence, which shows that two dT(CCG)3 A strands can associate to form a tetraplex structure with an i-motif core containing four C:C(+) pairs flanked by two G:G homopurine base pairs as a structural motif. The tetraplex core is attached to a short parallel-stranded duplex. Each hairpin itself contains a central CCG loop in which the nucleotides are flipped out and stabilized by stacking interactions. The helical twists between adjacent cytosine residues of this structure in the i-motif core have an average value of 30°, which is greater than those previously reported for i-motif structures

Topics: DNA structures, X-ray diffraction, i-motifs, neurological disease, tetraplex structures, Crystallography, X-Ray, DNA, Models, Molecular, Nucleic Acid Conformation, Trinucleotide Repeats
Year: 2015
DOI identifier: 10.1002/anie.201405637
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