Langmuir monolayers at the air-waterinterface is a proper technique to study the interfacial properties of filmforming peptides mixed with lipids. It allows to manipulate the lipid/peptidemole ratio, the amount of the Peptide Covered Area(PCA), the physical state of the lipid and the degree of lateralcompactness in a confined environment, mimicking a biological membraneinterface. Using lipid/peptide monolayers we studied the surface properties ofAβ(1-40) Amyloid Peptide (AP) mixed with POPC lipid andgangliosides.

At low peptide proportion, AP formsfibril-like structure in monolayers when mixed with POPC phospholipid withreproducible π-Area isotherms.  The maximal stability acquired by the mixedfilms is within 35-40 mN.m^-1 compatible with the equivalent surfacepressure postulated for natural biomembranes.

Pure AP forms insoluble monolayerswith high lateral stability without forming fibril-like structures. In aliquid-expanded lipid environment (POPC:AP mixture), we observed that bothmiscibility and stability of the film depend on PCA.  In the range of 2.5% to 10 % of PCA we observed fibril like structures. These fibril-likestructures are clearly observed with both BAM and AFM techniques. In thisexperimental condition, we found that GM1 and total brain gangliosides breakthese fibril-like structures indicating a lateral fibril-segregation imposed bythe presence of gangliosides at the mixed interface. This effect is observed at5-20 mole % of ganglioside with respect to POPC lipid. According to theliterature the effect of gangliosides on AP aggregation is controversial. Inour experimental condition gangliosides have a disaggregatingeffect.