Design of amphiphilic oligopeptides as models for fine tuning peptide assembly with plasmid DNA.

We discuss the design of novel amphiphilic oligopeptides with hydrophobic and cationic amino acids to serve as models to understand peptide-DNA assembly. Biophysical and thermodynamic characterization of interaction of these amphiphilic peptides with plasmid DNA is presented. Peptides with at least +4 charges favor stable complex formation. Surface potential is dependent on the type of hydrophobic amino acid for a certain charge. Thermodynamically it is a spontaneous interaction between most of the peptides and plasmid DNA. Lys(7) and Tyr peptides with +4/+5 charges indicate cooperative binding with pDNA without saturation of interaction while Val(2)-Gly-Lys(4), Val-Gly-Lys(5), and Phe-Gly-Lys(5) lead to saturation of interaction indicating condensed pDNA within the range of N/Ps studied. We show that the biophysical properties of DNA-peptide complexes could be modulated by design and the peptides presented here could be used as building blocks for creating DNA-peptide complexes for various biomedical applications, mainly nucleic acid delivery.

Influence of N-terminal hydrophobicity of cationic peptides on thermodynamics of their interaction with plasmid DNA.

There is a need to understand the thermodynamics of interaction of cationic peptides with DNA to design better peptide based non-viral gene delivery vectors. The main aim of this study was to understand the influence of N-terminal hydrophobicity of cationic amphiphilic peptides on thermodynamics of interaction with plasmid DNA. The model peptides used were TATPTD and TATPTDs modified at the N-terminal with hydrophobic amino acids. The thermodynamic binding data from isothermal titration calorimetry were compared with ethidium bromide analysis and ultrafiltration to correlate the binding parameters with the structural features of the various peptides used. It was observed that peptides having a smaller hydrophobic domain at the N-terminal have good DNA condensing ability compared with the ones with a longer hydrophobic domain. Calorimetry of peptides that reached saturation binding indicated that enthalpy and entropy are favorable for the interaction. Moreover, the interaction of these peptides with DNA appears to be predominantly electrostatic.

The effect of the structure of small cationic peptides on the characteristics of peptide-DNA complexes.

A series of transcriptional activator (TAT)-protein transduction domains (PTDs) modified with hydrophobic amino acids were used as model cationic amphiphilic peptides to study the effect of hydrophobicity on interaction of such peptides with plasmid DNA. The peptide-DNA complexes were analyzed by dynamic light scattering and gel electrophoresis to determine their size and electrokinetic properties at various +/- charge ratios. Peptides in solution were found to have a tendency to aggregate and the hydrodynamic size of the aggregates depends on the structure of peptide. Peptides with smaller hydrophobic residues at the N-terminal formed smaller complexes with DNA compared to the ones with larger hydrophobic tails. DNA complexes having peptides with more than one hydrophobic moiety at the N-terminal had a tendency to aggregate. Among the peptides having single hydrophobic amino acid at the N-terminal, DNA complexes of Tyr-TAT and Phe-TAT were found to be stable in solution. The size of the hydrophobic domain and the type of hydrophobic amino acid at the N-terminal of cationic amphiphilic peptides play an important role not only in the complex formation but also in stabilizing the system. The studies presented here indicate that there is a potential for strategic development of these peptides into potential non-viral gene delivery vectors.