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Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes
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Slow G-Quadruplex Conformation Rearrangement and Accessibility Change Induced by Potassium in Human Telomeric

Arianna N Lacen1, Andrew Symasek1, Alan Gunter1

  • 1Department of Chemistry, University of Alabama at Birmingham, 901 14th Street South, Birmingham, Alabama 35294, United States.

The Journal of Physical Chemistry. B
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Potassium ions (K+) stabilize G-quadruplexes (G4s) in telomeric DNA, reducing their dynamics and accessibility to complementary strands. This conformational change impacts telomeric overhang interactions in cellular environments.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • Guanine-rich telomeric DNA sequences can fold into G-quadruplex structures (G4s).
  • G4 formation influences the accessibility of single-stranded telomeric overhangs, critical for telomere maintenance.
  • Cations like sodium (Na+) and potassium (K+) are known to affect G4 stability and conformation.

Purpose of the Study:

  • To investigate the impact of Na+ and K+ on G-quadruplex folding and accessibility.
  • To understand the dynamics of cation exchange and its effect on G4 conformation and stability.
  • To elucidate the implications of these findings for telomeric overhang interactions in cellular contexts.

Main Methods:

  • Differential Scanning Calorimetry (DSC) to assess thermal stability.
  • Circular Dichroism (CD) spectroscopy to monitor structural changes.
  • Single-molecule Förster Resonance Energy Transfer (smFRET) to study conformational dynamics and strand binding accessibility.

Main Results:

  • G4s formed in K+ solutions exhibit lower conformational dynamics and higher thermal stability compared to those in Na+ solutions.
  • Na+ and K+ ions are shown to be exchangeable within the G4 structure.
  • Exposure to high K+ concentrations induces a slow conformational rearrangement in G4s, rendering them resistant to unfolding by complementary strands.

Conclusions:

  • K+ ions significantly stabilize telomeric G-quadruplexes, altering their conformational dynamics and accessibility.
  • The observed slow rearrangement in high K+ environments suggests a time-dependent change in G4 accessibility.
  • These findings provide critical insights into how G4 accessibility is modulated by cations, influencing telomeric overhang interactions with proteins and telomerase.