CONICET | Buscador de Institutos y Recursos Humanos

Langmuir monolayers at air-water interface is a proper techniqueto study the interfacial properties of film forming peptides mixed withlipids. It allows manipulating the lipid/peptide mole ratio, the amountthe Peptide Covered Area (PCA), the physical state of the lipid andthe degree of lateral compactness in a confined environment, mimickinga biological membrane interface. Using lipid/peptide monolayerswe studied the surface properties of AB1-40 Amyloid Peptide(AP) mixed with different proportions of lipid that differs in their physicalstate. As AP form beta-sheet conformation, we also include theamphiphilic alfa-helix Melittin peptide (Mel) for comparison. Both APand Mel form homogeneous monolayers with reproducible Pi-Areaisotherms and maximal stability in between 15-25 mN/m. Their rheologicalproperties were related to their secondary structures.In a liquid-condensed environment (DSPC/peptide mixed systems),we observed immiscible behavior at all proportions with afirst collapsing point close to that detected for pure peptide. In aliquid expanded lipid environment (POPC/peptide systems) bothmiscibility and stability of the film depend on the peptide used. ForPOPC/Mel at low PCA a mixed film exhibit composition-dependentstability, whereas at high PCA the lateral stability corresponds tothat of pure peptide, which together with BAM images indicates lateralsegregation induced by compression of the film. For AP/POPC,lateral segregation was observed (BAM images) at all proportions.However we found an unexpectedly complex stability behavior, correspondingto pure peptide at high PCA but composition-dependentat low PCA; interestingly at PCA 5-10% fibrils like structures areclearly observed and the film exhibit a pronounced compressionhysteresis. Surprisingly, fibrils could also be observed for DSPC/Melat certain proportions. We discuss on the conditions and kinetic aspectsaffecting fibrils formation.