Surface topography of lipid-peptide mixtures at the air-water interface using BAM: role of physical state of the lipid

CARUSO, B, AMBROGGIO EE, N. WILKE, FIDELIO GD

Carlos Paz, Cordoba

Congreso; 'XLII Reunión Anual de la Sociedad Argentina de Biofísica; 2013

Sociedad Argentina de Biofísica

Previous studies in our laboratory showed that the interaction of peptides with membrane lipids depend on the secondary structure of the former and the physical state of the latter (1, 2). Here, we contribute to this subject by imaging of Langmuir monolayers using the Brewster Angle Microscopy technique (BAM). Monolayer isotherms of the well-known Melittin did not present compressional hysteresis, in keeping with a prevalence of α-helix structure. Melittin form homogeneous monolayers at BAM, but when mixed with a lipid that forms Liquid Expanded (LE) monolayers (Tc,dmPC21ºC) it induced domain formation (phase segregation) at lateral pressures that dependent on film composition. Although pH affects the isotherm of pure Melittin, this did not affect the phase diagram of Melittin/DMPC. On the contrary, when mixed with the more liquid POPC (Tc,poPC -2ºC), the domains were not observed. On the other hand, the β-sheet Aβ1-42 peptide exhibits a different behaviour when mixed with either DMPC or POPC. In Aβ1-42/DMPC mixtures, although phase segregation did not occur at a defined lateral pressure, a fibrillar domain pattern became apparent upon compression. In Aβ1-42/POPC mixtures no domains were observed. We conclude that the physical state of lipid phase is not only important for lipid-peptide miscibility but also for lateral topography