A 'retro-inverso' PNA: structural implications for DNA and RNA binding

Area of Science:

• Chemical Biology
• Oligonucleotide Chemistry
• Biotechnology

Background:

• Peptide nucleic acids (PNAs) are DNA mimics with potential therapeutic applications.
• Modifications to the PNA backbone can alter hybridization properties and stability.
• Understanding backbone modifications is crucial for designing effective PNA-based agents.

Purpose of the Study:

• To synthesize and characterize retro-inverso peptide nucleic acid (PNA) monomers.
• To investigate the impact of retro-inverso modifications on PNA hybridization with DNA and RNA.
• To elucidate the conformational and energetic effects of backbone inversions in PNA.

Main Methods:

• Synthesis of retro-inverso thymine (T*) and adenine PNA monomers.
• Incorporation of T* monomers into PNA oligomers.
• Hybridization studies with complementary DNA and RNA oligonucleotides.
• Thermal denaturation (Tm) analysis.
• Molecular dynamics simulations.

Main Results:

• A homo retro-inverso T*8 PNA did not hybridize to complementary nucleic acids.
• A single T* unit in a PNA 15-mer destabilized hybridization by approximately 8°C.
• The T* backbone modification resulted in a -7°C effect with DNA and -4.5°C with RNA.
• T* units maintained sequence discrimination comparable to standard PNA.
• Molecular dynamics revealed unfavorable backbone conformation and electrostatic clashes.

Conclusions:

• Retro-inverso PNA backbone modifications introduce significant, unpredictable changes in hybridization properties.
• The T* modification destabilizes PNA-oligonucleotide complexes but preserves sequence recognition.
• Conformational constraints within the retro-inverso backbone impact PNA's DNA-mimicking capabilities.