Four-stranded DNA structure stabilized by a novel G:C:A:T tetrad.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Oligonucleotides can form complex three-dimensional structures beyond the canonical double helix.
• DNA quadruplexes, involving non-canonical base pairing, are crucial in various biological processes.
• Understanding novel DNA architectures is key to deciphering DNA-DNA interactions and functions.

Purpose of the Study:

• To determine the solution structure of the cyclic oligonucleotide d.
• To investigate the self-association behavior of this oligonucleotide under specific conditions.
• To characterize the novel four-stranded DNA architecture formed by the dimer.

Main Methods:

• Two-dimensional Nuclear Magnetic Resonance (2D NMR) spectroscopy for structural determination.
• Restrained molecular dynamics simulations to refine the structure.
• Analysis of base-pairing and ion coordination within the complex.

Main Results:

• The cyclic oligonucleotide d self-associates to form a symmetric dimer.
• A novel G:C:A:T tetrad, stabilized by a Na(+) cation, was identified.
• The dimer adopts a four-stranded structure with minor groove alignment of Watson-Crick base pairs.
• This represents the first observation of this specific G:C:A:T tetrad in an oligonucleotide structure.

Conclusions:

• The discovery of the G:C:A:T tetrad expands the known repertoire of DNA four-stranded architectures.
• The observed structure shares similarities with other quadruplexes, suggesting a general motif for DNA-DNA recognition.
• This finding has implications for understanding sequence-specific DNA interactions and potential therapeutic targets.