Structure and dynamics of peptide-polynucleotide complexes

Area of Science:

• Molecular Biology
• Biophysics
• Biochemistry

Background:

• Understanding the binding dynamics of peptides to nucleic acids is crucial for molecular biology.
• LysTrpLys, a peptide containing tryptophan, interacts with DNA and RNA, but the precise mechanism and structural implications are not fully understood.

Purpose of the Study:

• To elucidate the binding mechanism and dynamics of LysTrpLys with double-helical DNA and single-stranded poly(A).
• To investigate the structural and dynamic consequences of tryptophan indole residue insertion into nucleic acids.

Main Methods:

• Chemical relaxation measurements using fluorescence detection after electric field pulses.
• Rotational diffusion analysis via electric dichroism.
• Global fitting analysis of experimental data to a two-step reaction model.
• Comparison with other Lys-X-Lys peptides (LysTyrLys, LysLeuLys, LysGlyLys).

Main Results:

• LysTrpLys binding follows a two-step mechanism: a diffusion-controlled bimolecular reaction followed by a slow intramolecular insertion of indole residues.
• The insertion rate is dependent on nucleic acid type, chain length, and ionic strength.
• Insertion into DNA does not significantly increase helix length, suggesting partial insertion, and differs dynamically and structurally from intercalation.

Conclusions:

• The binding of LysTrpLys to DNA and RNA involves a distinct insertion mechanism, not intercalation.
• The structural impact of indole insertion on DNA is minimal, indicating a unique mode of interaction.
• These findings provide insights into peptide-nucleic acid interactions and the behavior of aromatic residues within nucleic acid structures.