Understanding the Interaction of Polymeric Polypeptides with Liposomes

The study of polymeric polypeptides and their interaction with liposomes presents fascinating insights into membrane biophysics. One notable observation is how negatively charged lipids can shift the local pH towards more acidic conditions, promoting the protonation of carboxyl groups in polymers. This shift increases the hydrophobicity of the polymers, enhancing their ability to penetrate phospholipid membranes. This intricate mechanism is crucial for applications in drug delivery and membrane technology.

Research conducted by Ferenc Hudecz et al. has highlighted the significant effects of polymeric polypeptides on phospholipid bilayers, particularly those composed of DPPC (Dipalmitoylphosphatidylcholine) and varying amounts of PG (Phosphatidylglycerol). The degree of interaction varies with the composition of the liposome, with polycationic polypeptides such as OAK and polylysine showing pronounced effects on the polarization of the bilayer. These interactions are influenced by temperature, which plays a critical role in the phase transition behaviors of the liposomes.

As temperature increases, the presence of PG in the bilayer leads to enhanced fluidity, and this is reflected in the changes observed in polarization values. For instance, bilayers with 5% PG exhibit a notable decrease in polarization at elevated temperatures, indicative of a crystalline phase transition. Conversely, polylysine demonstrates a consistent increase in polarization across the tested temperature range, suggesting its strong interaction with the bilayer.

Interestingly, the influence of various polypeptides on the fluidity of the bilayer varies significantly. While polylysine exhibits a rigorous effect, others like AK, SAK, and EAK show either no influence or only a moderate impact. Additionally, the presence of a higher proportion of negatively charged lipids enhances the interaction with polymeric polypeptides, potentially due to changes in the viscosity of the bilayer.

The behavior of these polypeptides at the air/water interface further underscores their complex interactions with phospholipid membranes. The stability and penetration kinetics of these polymers depend on their charge and structural properties. Notably, the hierarchical effectiveness of different polypeptides can be ranked as SAK > AK > EAK > Ac-EAK > OAK > polylysine, revealing the nuanced roles these molecules play in bilayer dynamics.

Through ongoing research, the understanding of polymeric polypeptides' interactions with liposomes continues to evolve, shedding light on their potential uses in biomedicine and material sciences. This knowledge paves the way for innovations in targeted drug delivery systems, where manipulation of membrane interactions is paramount.