Triplex-Forming Peptide Nucleic Acids with Extended Backbones.

Area of Science:

• Biochemistry
• Molecular Biology
• Chemical Biology

Background:

• Peptide nucleic acid (PNA) forms triple helices with double-stranded RNA (dsRNA), stabilized by hydrogen bonds between PNA backbone amides and RNA phosphate oxygens.
• This interaction is facilitated by a specific spacing (∼5.7 Å) between PNA backbone amides and RNA phosphate groups, characteristic of A-form dsRNA.

Purpose of the Study:

• To investigate if extending the PNA backbone by one -CH₂- group could alter binding affinity for double-stranded DNA (dsDNA) and dsRNA.
• To test the hypothesis that a modified PNA backbone (closer to 7 Å spacing) would selectively stabilize PNA-DNA triplexes over PNA-RNA triplexes.

Main Methods:

• Synthesis of PNA analogues with extended pseudopeptide backbones at three different positions.
• Isothermal titration calorimetry (ITC) to measure binding affinities of modified PNAs to matched dsDNA and dsRNA.

Main Results:

• Contrary to the hypothesis, extending the PNA backbone at any position significantly reduced triplex stability for both dsDNA and dsRNA.
• The modifications negatively impacted the binding affinity, indicating a loss of stability in the PNA-nucleic acid triplexes.

Conclusions:

• The study suggests that PNAs possess an inherent preference for binding A-form nucleic acids, such as dsRNA.
• The original six-atom PNA backbone structure is highly optimized for binding A-form nucleic acids, and modifications disrupt this favorable interaction.