Integration of Surface-Active, Periodically Sequenced Peptides into Lipid-Based Microbubbles

Abstract

The development of microbubbles toward functional, "theranostic" particles requires the incorporation of constituents with high binding specificity and therapeutic efficacy. Integrating peptides or proteins into the shell of lipid-based microbubbles can provide a means to access both receptor-ligand interactions and therapeutic properties. Simultaneously, peptides or proteins can define the characteristic monolayer mechanics of lipid bubbles and eliminate the need for post-bubble generation modification. The ability to engineer peptide sequences de novo that effectively partition into the bubble monolayer remains parametrically daunting. This work contributes to this effort using two simple amphipathic helical peptides that examine the role of local electrostatics and secondary structure. The two periodically sequenced peptides both have three positive charges, but peptide "K-2.5" spaces those charges 2.5 amino acids apart, while peptide "K-6.0" spaces the charges six amino acids apart. Size populations were determined for bubbles containing each peptide species using light scattering, and a quantitative method was developed to clearly define the fraction of peptides binding onto the microbubble monolayer. The impact of both the initial peptide concentration and the zwitterionic:anionic lipid ratio on peptide binding was also evaluated. Our results indicate that the lipid ratio affected only K-6.0 binding, which appears to be an outcome of the greater ensemble average α-helical population of the K-6.0. These findings provide further insights into the role of charge separation on peptide secondary structure, establishing a simple design metric for peptide binding onto microbubble systems.

Adsorption of rationally designed “surf-tides” to a liquid-crystal interface

“…20 Briefly, both model molecules were designed to examine the role of charge distribution along the peptide backbone on both secondary structure and surface activity. 20 Briefly, both model molecules were designed to examine the role of charge distribution along the peptide backbone on both secondary structure and surface activity.…”

“…20 Upon folding, the hydrophobic face contains both alanine and leucine residues, neither of which contains linear acyl chains of significant length. 20 Upon folding, the hydrophobic face contains both alanine and leucine residues, neither of which contains linear acyl chains of significant length.…”

“…The design of the two rationally designed peptides used in these experiments was discussed in detail previously. 20 Briefly, both model molecules were designed to examine the role of charge distribution along the peptide backbone on both secondary structure and surface activity. Our design methodology follows two well-cited design 'rules': intrinsic propensity and periodicity.…”

“…In the case of the two model peptides examined in this study, we have previously shown that upon binding to an interface, the folded structure is the dominant species. 20 Upon folding, the hydrophobic face contains both alanine and leucine residues, neither of which contains linear acyl chains of significant length. Additionally, the peptide backbone presents torsional angle restrictions down the length of the molecules further limiting an arrangement of hydrophobic side groups that would promote a homeotropic state.…”