The Plasticins:  Membrane Adsorption, Lipid Disorders, and Biological Activity

Abstract

The present study investigates the relationships between structural polymorphism, adsorption onto membrane mimetic support, lipid disturbance, and biological activity of bactericidal 23-residue, glycine-leucine-rich dermaseptin orthologues from the Phyllomedusinae frog skin, the "plasticins". Biological activities were evaluated using the membrane models DMPG (1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol) for prokaryotic membranes and DMPC (1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine) for eukaryotic membranes. We performed a conformational analysis of plasticins by molecular simulations and spectroscopic methods and analyzed phospholipid perturbations by infrared spectroscopy. Adsorption onto synthetic model membranes was quantified by surface plasmon resonance. Biological assays including antimicrobial and membrane potential-dissipating activities, together with hemolytic tests and imaging analysis of cytotoxicity, were carried out to clarify the peptide-membrane interactions. Two major groups were distinguished: (i) Neutral plasticins revealed the presence of strong beta-structures with the zwitterionic or anionic phospholipid vesicles. They were weakly adsorbed in the range of antibacterial activity concentrations (micromolar). Nevertheless, for millimolar concentrations, they caused perturbations at the interface peptide-DMPG vesicles and in the bilayer alkyl chains, suggesting insertion into bacterial membranes. (ii) Cationic plasticins revealed multiple conformational transitions, including destabilized helix states, beta-structures, and disordered states. Peptide-lipid complex densities depended on hydrophobic bond strengths. The most soluble cationic plasticins were strongly adsorbed, with stable peptide-lipid interactions inducing noticeable perturbations of bilayer alkyl chains, pointing out possible insertion into bacterial membranes. In contrast, cytotoxic plasticins were less adsorbed, with less stable peptide-lipid interactions causing membrane dehydration, formation of peptide-membrane hydrogen bonds, and little disturbances of lipid alkyl chains. These characteristics could be compatible with their putative action on intracellular targets leading to apoptosis.

Structural malleability of plasticins: Preorganized conformations in solution and relevance for antimicrobial activity

“…This distance was 30-35 Å for a-helical structure and 70-80 Å for a totally extended structure. 1,3 In Figure 6A,CaG1-CaG23 distances compatible with b-hairpin conformations are those for PD36 and PD36KF. They underwent transitions between three conformations (helix/coil/b-hairpin shaped structure) with different coil transition states, more extended for PD36 (CaG1-CaG23 & 40 Å ) than PD36KF (CaG1-CaG23 & 15-20 Å ).…”

“…In previous papers, we have shown that the presence of K8, K12 lysines were determinant for antimicrobial activity. 1,3 So, the contribution of these residues was investigated within PD36 series: PD36, two virtual mutants (PD36K 8, PD36K 12 ) and the analogous PD36K 8 K 12 . Figure 7 pointed out the large conformational behavior splitting for the studied series.…”

“…The data demonstrated that evolution has positively selected charge-altering nucleotide substitutions to generate from an otherwise neutral ancestral hemolytic peptide orthologous cationic variants that bind to and permeate bacterial cell membranes. 1,3 This process leads to the selection of lysine residues. In a recent work, we have underlined the impact of structural polymorphism of plasticins on adsorption process onto mimetic membranes, lipid packing disturbance, and antimicrobial or cytotoxic activities.…”

“…In a recent work, we have underlined the impact of structural polymorphism of plasticins on adsorption process onto mimetic membranes, lipid packing disturbance, and antimicrobial or cytotoxic activities. 3 Plasticins adopted various structural fitting in the vicinity of membrane mimetic supports. Neutral plasticins with strong b-structures revealed in the presence of phospholipid vesicles were weakly adsorbed at micromolar concentrations where they manifested no antimicrobial activity.…”

“…Curve fitting was performed using PAMIR program to calculate the relative abundance of each structure component in the transmission and ATR-FTIR experiments. 3 …”