FIBRILLIKE STRUCTURES CAN BE INDUCED IN LIPID/PEPTIDE

(Beta-AMYLOIDAND MELITTIN) LANGMUIR MONOLAYERS

BolañoAlvarez, A1,  Caruso, B2  and Fidelio, GD1

1Departamento de Química Biológica RanwelCaputto, Facultad de Ciencias Químicas y Centro de Investigaciones en QuímicaBiológica de Córdoba, CIQUIBIC, CONICET, Universidad Nacional de Córdoba.

2Instituto de InvestigacionesBiológicas y Tecnológicas IIBYT, CONICET, Universidad Nacional de Córdoba.

Langmuirmonolayers at air-water interface is a proper technique to study theinterfacial properties of film forming peptides mixed with lipids. It allowsmanipulating the lipid/peptide mole ratio, the amount the Peptide CoveredArea (PCA), thephysical state of the lipid and the degree of lateral compactness in a confinedenvironment, mimicking a biological membrane interface. Using lipid/peptidemonolayers we studied the surface properties of AB1-40 Amyloid Peptide(AP) mixed with different proportionsof lipid that differs in their physical state. As AP form beta-sheetconformation, we also include the amphiphilic alfa-helix Melittin peptide (Mel) forcomparison. Both AP and Mel form homogeneous monolayers with reproduciblePi-Area isotherms and maximal stability in between 15-25 mN/m.Their rheological properties were related to their secondary structures.

In aliquid-condensed environment (DSPC/peptide mixed systems), we observedimmiscible behavior at all proportions with a first collapsing point close tothat detected for pure peptide. In a liquid expanded lipid environment(POPC/peptide systems) both miscibility and stability of the film depend on thepeptide used. For POPC/Mel. at low PCA a mixed film exhibitcomposition-dependent stability, whereas at high PCA the lateral stabilitycorresponds to that of pure peptide, which together with BAM images indicateslateral segregation induced by compression of the film. For AP/POPC, lateralsegregation was observed (BAM images) at all proportions. However we found anunexpectedly complex stability behavior, corresponding to pure peptide at highPCA but composition-dependent at low PCA; interestingly at PCA 5-10% fibrilslike structures are clearly observed and the film exhibit a pronouncedcompression hysteresis. Surprisingly, fibrils could also be observed forDSPC/Mel at certain proportions. We discuss on the conditions and kineticaspects affecting fibrils formation.