Aggregation, Fusion, and Leakage of Liposomes Induced by Peptides

Biological membranes are heterogeneous systems. Their functions are closely related to the lipid lateral segregation in the presence of membrane proteins. In this work, we designed two peptides, amphiphilic cationic peptides K₃L₈K₃ and nonamphiphilic peptides K₂₀, and studied their interactions with binary liposomes in different phases (<i>L</i>_α, <i>L</i>_β′, and <i>L</i>_α/<i>L</i>_β′). As mimics of membrane proteins, both K₃L₈K₃ and K₂₀ can cause the liposomes to aggregate, fuse, or leak. These processes were closely related to the phases of liposomes. For the liposomes in <i>L</i>_α phase, heavy aggregation, fusion, and leakage were observed in the presence of either K₂₀ or K₃L₈K₃. For the liposomes in <i>L</i>_β′ phase, neither K₃L₈K₃ nor K₂₀ can induce fusion or leakage. For the liposomes in <i>L</i>_α/<i>L</i>_β′ phase, K₃L₈K₃ caused the liposomes to aggregate, fuse, and leak, while K₂₀ only led to aggregation. The kinetics of aggregation, fusion, and leakage in each phase were recorded, and they were related to the lipid demixing in the presence of the peptide. Our work not only gained insight into the effect of the lipid demixing on the interactions between peptide and membrane, but also helped in developing drug delivery vehicles with liposomes as the platform

LLS studies on plasmid DNA (A: size distribution at 30°, B: angular dependence of excess scattered intensity) and calf thymus DNA (A': size distribution at 30°, B': angular dependence of excess scattered intensity).

<p>C = 1.6×10⁻⁵ g/ml.</p

Thermal denature curve of 21bp DNA fragment in 95% DMF.

<p>C = 20 µg/mL.</p

LLS results of plasmid DNA and calf thymus DNA in TE buffer and in 95%DMF.

<p>LLS results of plasmid DNA and calf thymus DNA in TE buffer and in 95%DMF.</p

Agarose gel electrophoresis of DNA samples.

<p>(A) Plasmid DNA: M_W marker (lane 1), control DNA (lane 2), control DNA cut with <i>Eco</i>RI, which linearized the plasmid but would not alter the size (lane 3), control DNA cut with <i>Pst</i>I showing 2 fragments with different lengths (lane 4), DNA treated with DMF and cut with <i>Eco</i>RI (lane 5) or <i>Pst</i>I (lane 6); (B) Calf thymus DNA: M_W marker (lane 1), control DNA (lane 2), DNA treated with water (lane 3), DNA treated with DMF (lane 4).</p

DMF-content dependence of zeta potential measurements of calf thymus DNA and plasmid DNA.

<p>DMF-content dependence of zeta potential measurements of calf thymus DNA and plasmid DNA.</p

TEM measurements of (A) calf thymus and (B) plasmid DNA air dried from 95% DMF.

<p>TEM measurements of (A) calf thymus and (B) plasmid DNA air dried from 95% DMF.</p

Thermal denature curves of calf thymus and plasmid DNA.

<p>Plasmid DNA: hollow symbols; calf thymus DNA: solid symbols. C = 16 µg/mL.</p

Temperature effect on hydrodynamic radius of plasmid DNA in 95% DMF at 30°.

<p>The inset shows the temperature dependence of R_h,app at zero angle.</p

Assembly and Reassembly of Polyelectrolyte Complex Formed by Poly(ethylene glycol)-<i>block</i>-poly(glutamate sodium) and S₅R₄ Peptide

The structure and stability of polyelectrolyte complex are controlled not only by electrostatic interaction but also by hydrogen bonding and hydrophobic interaction if they are present. The complexes formed by such multiple interactions should exhibit different responses to the environmental changes, such as ionic strength and pH. In this work, we designed a positively charged peptide S₅R₄, which can interact with poly­(ethylene glycol)-<i>block</i>-poly­(glutamate sodium) (PEG₁₁₄-PGlu₆₄) via electrostatic interaction, hydrogen bonding, and hydrophobic interaction. In deionized water at pH 7.1, the complexes formed by PEG₁₁₄-PGlu₆₄ and S₅R₄ assemble into wormlike micelles, spheres, and even hierarchical “wool balls”, depending on mixing ratio. However, a distinct dissociation–reassembly process is observed when 30 mM NaCl is added to screen the electrostatic interaction. The spheres transform into loose clusters after reassembly. This process is caused by the switch of driving force from electrostatic interaction to hydrogen bonding. Similarly, when the driving force is switched from electrostatic interaction to hydrophobic interaction by increasing solution pH to above 8.7, the original structure quickly dissociates and reassembles into dense aggregates. The rich structures formed by polyelectrolyte complexes and their drastic and sensitive responses to environmental changes are helpful to understand the working mechanism of biomolecules regulated by pH or ion strength