Destabilization of i-Motif by Submolar Concentrations of a Monovalent Cation
- Authors
- Kim, Sung Eun; Lee, Il-Buem; Hyeon, Changbong; Hong, Seok-Cheol
- Issue Date
- 8-5월-2014
- Publisher
- AMER CHEMICAL SOC
- Citation
- JOURNAL OF PHYSICAL CHEMISTRY B, v.118, no.18, pp.4753 - 4760
- Indexed
- SCIE
SCOPUS
- Journal Title
- JOURNAL OF PHYSICAL CHEMISTRY B
- Volume
- 118
- Number
- 18
- Start Page
- 4753
- End Page
- 4760
- URI
- https://scholar.korea.ac.kr/handle/2021.sw.korea/98526
- DOI
- 10.1021/jp500120d
- ISSN
- 1520-6106
- Abstract
- Counterions are crucial for self-assembly of nucleic acids. Submolar monovalent cations are generally deemed to stabilize various types of base pairs in nucleic acids such as Watson-Crick and Hoogsteen base pairs via screening of electrostatic repulsion. Besides monovalent cations, acidic pH is required for i-motif formation because protons facilitate pairing between cytosines. Here we report that Li+ ions destabilize i-motif, whereas other monovalent cations, Na+ and K+, have the usual stabilizing effect. The thermodynamics data alone, however, cannot reveal which mechanism, enhanced unfolding or suppressed folding or both, is responsible for the Li+-induced destabilization. To gain further insight, we examined the kinetics of i-motif. To deal with slow kinetics of i-motif, we developed a method dubbed HaRP to construct a long FRET time trace to observe a sufficient number of transitions. Our kinetics analysis shows clearly that Li+ ions promote unfolding of i-motif but do not hinder its folding, lending strong support for our hypothesis on the origin of this unusual effect of Li+. Although the subangstrom size of Li+ ions allows them to infiltrate the space between cytosines in competition with protons, they cannot adequately fulfill the role of protons in mediating the hydrogen bonding of cytosine pairs.
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