Structural competition involving G-quadruplex DNA and its complement.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Repetitive DNA sequences can form various structures like G-quadruplexes, I-motifs, and Watson-Crick duplexes.
• The competitive mechanisms governing the formation of these DNA structures are not fully understood.

Purpose of the Study:

• To investigate the influence of sequence context, cation species, and pH on DNA duplex formation.
• To elucidate the competitive mechanism between G-quadruplex, I-motif, and Watson-Crick duplex formation.

Main Methods:

• Isothermal Titration Calorimetry (ITC)
• Differential Scanning Calorimetry (DSC)
• Polyacrylamide Gel Electrophoresis (PAGE)
• Circular Dichroism (CD) spectroscopy
• UV-Vis spectroscopy
• CD stopped-flow kinetic studies

Main Results:

• Watson-Crick duplex formation was confirmed for complementary G-rich and C-rich DNA strands.
• Duplex formation showed a significantly higher binding constant (5.28 x 10^7 M^-1) in 10 mM Mg(2+) at pH 7.0 compared to 100 mM Na(+) at pH 5.5.
• The rate of duplex formation was approximately 10 times faster at pH 7.0 (8.06 x 10^-3 s^-1) than at pH 5.5, with dissociation of single-stranded structures identified as the rate-limiting step.
• Observed rates increased with temperature, supporting the rate-limiting step conclusion.

Conclusions:

• pH plays a critical role in modulating the structural competition between G-quadruplex, I-motif, and Watson-Crick duplexes.
• The findings suggest that I-motif structures may have a biological regulatory function.
• Understanding these structural dynamics is crucial for comprehending DNA sequence behavior and potential biological roles.