Oligonucleotide-Peptide Complexes: Phase Control by Hybridization.

Area of Science:

• Polymer Science
• Biophysical Chemistry
• Molecular Biology

Background:

• Counterion release drives phase separation in oppositely charged polymer mixtures, a critical unsolved problem.
• Nucleic acids, highly charged polyanions, condense via basic proteins in cells (chromatin) and form membraneless organelles.
• Electrostatic interactions are key for assembling nanoparticles for therapeutic nucleic acid delivery.

Purpose of the Study:

• To investigate the phase behavior of complexes formed between oligonucleotides and cationic peptides.
• To understand how nucleic acid structure and charge density influence complex formation and phase separation.
• To explore the potential of these complexes for responsive therapeutic and sensing applications.

Main Methods:

• Complexation experiments with oligonucleotides (RNA, methylphosphonate backbones) and cationic peptides.
• Varying polymer lengths, concentrations, and structures.
• Investigating the effect of salt concentration on complex phase.

Main Results:

• The hybridization state of nucleic acids controls the phase of the complexes: double-stranded forms solid precipitates, single-stranded forms liquid coacervates.
• Lower charge density of single-stranded oligonucleotides contributes to liquid coacervate formation.
• Salt addition transforms precipitates into coacervates, and coacervate-bound oligonucleotides retain hybridization competence.

Conclusions:

• Nucleic acid hybridization state is a critical determinant of complex phase behavior.
• Oligonucleotide complexes can transition between solid and liquid phases in response to environmental stimuli like salt concentration.
• These findings suggest potential for creating environmentally responsive complexes and nanoparticles for advanced applications.