Surface properties of amphiphilic peptides at air/water interface

FIDELIO G.D

Caxambu

Conferencia; XXIX Reuniao Anual; 2014

FeSBE

Surface Properties of Amphiphilic peptides at Air/Water Interface

            Modern view of natural membranes has been updated from the original vision emerged from the Fluid Mosaic Model of Singer and Nicolson published in 1972. One of highlighted feature of the new vision is the acceptance of a high density of proteins mixed with lipids organized as a bilayer forming a continuous hydrophobic/hydrophilic limit that dynamically controls the function of biomembranes in the cell. Langmuir monolayers at the air/water interface is practically the unique technique allowing the study of the surface properties of peptides and proteins and their interaction with lipids in a confined ?crowded? condition similar to the that found in natural biomembranes. Even more, the experimental conditions, as the surface covered proportion of the peptide compared with the lipid one or the degree of surface compactness, are quite controlled at will by the investigator. Using Langmuir monolayer many studies can be performed such us: ability of peptides to absorb to clean air/water interfaces (tensio-active properties),  to interact with organized lipid monolayers (penetration), surface stability of spread protein/peptide sample, peptide/lipid lateral miscibility, surface rheology, conformation and secondary structure by PM-IRRAS and lateral topography by using the Brewster Angle Microscopy technique (BAM).             Even when the proteins and short peptides are so diverse in sequence (and therefore amphiphilicity and structure) some generalities can be achieved regarding to their surface behavior at water/air interface. Water soluble amphipathic proteins and peptides acquire similar surface properties independently they absorbed from bulk aqueous phase or spread from aqueous or from an appropriate organic solvent solution; a higher stability upon lateral compression is observed with hydrophobic peptides with a higher tendency to adopt a β-sheet conformation at the interface compared with those with a higher tendency to adopt an α-helix and, in turn, this higher stability confers a greater tendency to remain miscible in mixed lipid-peptide systems; some representative pure peptide monolayers have similar properties than lipids when their surface characteristics are compared (lateral stability and  surface potential) and, a higher liquid-expanded character of the lipid at the interface confers a more adequate lateral environment for bidimensional miscibility. Finally, amyloidogenic peptides such as Aβ1-42 amyloid peptide with a higher tendency to adopt β-sheet conformation has a remarkable shear elasticity modulus when compared to lytic melittin compatible with a fiber-like topography at the surface found for the former.