Stress-induced acidification may contribute to formation of unusual structures in C9orf72-repeats |
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Authors: | Bita Zamiri Mila Mirceta Rashid Abu-Ghazalah Marc S Wold Christopher E Pearson Robert B Macgregor |
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Institution: | 1. Graduate Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario M5S 3M2, Canada;2. Program of Genetics & Genome Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada;3. Program of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A1, Canada;4. W. Booth School of Engineering Technology Practice and Technology, McMaster University, Hamilton, Ontario L8S 0A3, Canada;5. Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA |
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Abstract: | BackgroundExpansion of the C9orf72 hexanucleotide repeat (GGGGCC)n·(GGCCCC)n is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Both strands of the C9orf72 repeat have been shown to form unusual DNA and RNA structures that are thought to be involved in mutagenesis and/or pathogenesis. We previously showed that the C-rich DNA strands from the C9orf72 repeat can form four-stranded quadruplexes at neutral pH. The cytosine residues become protonated under slightly acidic pH (pH?4.5–6.2), facilitating the formation of intercalated i-motif structures.MethodsUsing CD spectroscopy, UV melting, and gel electrophoresis, we demonstrate a pH-induced structural transition of the C-rich DNA strand of the C9orf72 repeat at pHs reported to exist in living cells under stress, including during neurodegeneration and cancer.ResultsWe show that the repeats with lengths of 4, 6, and 8?units, form intercalated quadruplex i-motifs at low pH (pH?<?5) and monomolecular hairpins and monomolecular quadruplexes under neutral-basic conditions (pH?≥?8). Furthermore, we show that the human replication protein A (RPA) binds to the G-rich and C-rich DNA strands under acidic conditions, suggesting that it can bind to i-motif structures.ConclusionsIn the proper sequence context, i-motif structures can form at pH values found in some cells in vivo.General significanceDNA conformational plasticity exists over broad range of solution conditions. |
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Keywords: | c9orf72 G-Quadruplex I-motif Circular dichroism spectroscopy DNA structure Protein-DNA interactions |
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