Antimicrobial and cell-penetrating peptides induce lipid vesicle fusion by folding and aggregation

Abstract

According to their distinct biological functions, membrane-active peptides are generally classified as antimicrobial (AMP), cell-penetrating (CPP), or fusion peptides (FP). The former two classes are known to have some structural and physicochemical similarities, but fusogenic peptides tend to have rather different features and sequences. Nevertheless, we found that many CPPs and some AMPs exhibit a pronounced fusogenic activity, as measured by a lipid mixing assay with vesicles composed of typical eukaryotic lipids. Compared to the HIV fusion peptide (FP23) as a representative standard, all designer-made peptides showed much higher lipid-mixing activities (MSI-103, MAP, transportan, penetratin, Pep1). Native sequences, on the other hand, were less fusogenic (magainin 2, PGLa, gramicidin S), and pre-aggregated ones were inactive (alamethicin, SAP). The peptide structures were characterized by circular dichroism before and after interacting with the lipid vesicles. A striking correlation between the extent of conformational change and the respective fusion activities was found for the series of peptides investigated here. At the same time, the CD data show that lipid mixing can be triggered by any type of conformation acquired upon binding, whether α-helical, β-stranded, or other. These observations suggest that lipid vesicle fusion can simply be driven by the energy released upon membrane binding, peptide folding, and possibly further aggregation. This comparative study of AMPs, CPPs, and FPs emphasizes the multifunctional aspects of membrane-active peptides, and it suggests that the origin of a peptide (native sequence or designer-made) may be more relevant to define its functional range than any given name.

Recent Results in Alamethicin Research

“…ALM is applied these days as an "etalon" or control in several cases for the characterization of conduction features of novel pore-forming molecules [10−12]. Its fusogenic effect was also tested on lipid vesicles as one of the gold standards of membrane activity, but it was completely inactive in the applied experimental setup [13].…”

Mechanism Matters: A Taxonomy of Cell Penetrating Peptides

“…When cationic CPPs are bound to anionic bilayers, especially when the peptide-to-lipid ratio is high (P:L ≥ 1:50), many effects are observed. Bilayer curvature can change [53–55], membrane domain architecture can be affected[47,54], non-bilayer phases can form[56], domains of clustered lipids and peptides can form[54,57], bilayer disorder can increase[53] or decrease[58], vesicles can undergo aggregation and fusion[59], lipid flip-flop can occur[56], and entrapped contents can be released [49–51]. Which of these effects occurs, if any, is dependent on the CPP sequence, the peptide to lipid ratio, the lipid composition and many other experimental details.…”

‘Smart’ nanoparticles as drug delivery systems for applications in tumor therapy

“…However, fusogenic liposomes, which fuse conventional liposomes with peptides, are able to successfully overcome these two obstacles in an endocytosis-independent manner during delivering drugs into cytoplasm [41,42]. In fact, conventional liposomes are also taken up by endocytosis, but the peptides have membrane fusogenic activity.…”

“…Initially, these peptides come from the viral and cellular fusion proteins in nature. Now, transportan, transactivating transcriptional factor of HIV-1 and cell-penetrating peptides can be used as the peptides with membrane fusogenic activity [41,42].…”