Conformational flexibility in DNA duplexes containing single G.G mismatches

Area of Science:

• Molecular Biology
• Biophysics
• Structural Biology

Background:

• Purine-purine mismatches, specifically Guanine-Guanine (G.G), can adopt diverse configurations in DNA duplexes.
• Previous studies suggested G.G mismatches form G(anti).G(syn) pairs or weakly hydrogen-bonded G(anti).G(anti) pairs.
• Detailed structural analysis of these mismatches is challenging due to spectral overlap and exchange processes.

Purpose of the Study:

• To characterize the conformations of DNA duplexes containing single G.G mismatches using Nuclear Magnetic Resonance (NMR).
• To investigate the dynamic behavior and conformational states of mismatched Guanine residues in solution.

Main Methods:

• NMR spectroscopy was employed to analyze four DNA duplexes with single G.G mismatches.
• Nuclear Overhauser Effect (NOE) experiments and coupling constant analysis were used to determine conformations.
• Rotating frame T1 measurements were utilized to determine the rate of conformational transitions.

Main Results:

• All four duplexes exhibited evidence of conformational exchange at the G.G mismatch site.
• NMR data indicated that mismatched Guanine residues adopt syn conformations.
• Analysis suggested an equimolar mixture of G(syn).G(anti) and G(anti).G(syn) states in self-complementary duplexes.
• The rate constant for syn/anti transition in a non-self-complementary undecamer was determined to be approximately 14,000 s⁻¹ at 303 K.

Conclusions:

• G.G mismatches in DNA duplexes exist in a dynamic equilibrium between syn and anti conformations.
• The study provides insights into the structural flexibility and conformational dynamics of mismatched DNA bases.
• The overall DNA duplexes maintain the B-form structure despite the presence of G.G mismatches.