Biophysical Society Thematic Meeting | Ascona, Switzerland

Liposomes, Exosomes, and Virosomes: From Modeling Complex Membrane Processes to Medical Diagnostics and Drug Delivery

Monday Speaker Abstracts

Use of Model Membranes-Liposomes and Micelles of Variable Lipid Composition to Elucidate the Molecular Mechanism of Action of Pore-forming Proteins and Peptides Gustavo P. Carretero 1 , Eduardo M. Cilli 2 , Carlos Alvarez 3 , Shirley Schreier 1 . 1 University of Sao Paulo, Sao Paulo, Sao Paulo, Brazil, 2 State University of Sao Paulo, Araraquara, Sao Paulo, Brazil, 3 University of La Habana, La Habana, Cuba. Sticholysins I and II, cytolysins purified from the sea anemone Stichodactyla helianthus, lyse biological and model membranes. The proposed mechanism of action consists of the formation of a toroidal pore involving the N-terminal domain. The interaction between peptides from the toxins’ N-termini (StI1-31 and StI12-31 SELAGTIIDGASLTFEVLDKVLGELGKVSRK, and StII1-30 and StII11-30 ALAGTIIAGASLTFQVLDKVLEELGKVSRK) and model membranes – liposomes and micelles – was studied in order to contribute to the elucidation of the toxins mechanism of action at the molecular level. Peptides were used based on the hypothesis that protein fragments can mimic the structure and activity of the whole protein. An analogue containing the paramagnetic amino acid TOAC (N-TOAC-StII11-30) was also studied. Conformational studies made use of circular dichroism (CD), electron paramagnetic resonance (EPR), and fluorescence. Studies of structure prediction and molecular modeling were also performed. The peptides acquired α-helical conformation upon interaction with model lipid membranes, in agreement with the conformation found for these segments in the whole proteins. Studies with membranes of variable lipid composition, demonstrated that both electrostatic and hydrophobic interactions contribute to peptide binding. Fluorescence quenching of labeled lipids by paramagnetic TOAC and EPR spectra allowed us to locate the TOAC residue at the membrane-water interface, corroborating the proposed model of the toroidal pore. CD and EPR studies also allowed calculation of peptide-membrane binding constants. The peptides also mimicked the toxins function, as shown by assays of carboxyfluorescein leakage and hemolytic activity. Short peptides containing parts of StII1-30’s sequence were synthesized with the aim of testing their antimicrobial activity. The peptides displayed low antimicrobial activity, as well as lack of hemolytic activity and toxicity against human cells.

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