The rheological properties of beta amyloid peptide monolayers: comparative studies with lytic melittin

B. CARUSO; AMBROGGIO, EE; WILKE, N.; FIDELIO, G

COLLOIDS AND SURFACES B-BIOINTERFACES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 146 p. 180 - 187

0927-7765

We determined the rheological propertiesof b-amyloid Langmuir films at the air/waterinterface, a peptide whose interfacial structure is extended b-sheet, and compared them with those offilms composed of Melittin (Mel), which adopts an a-helicalconformation at neutral pH. To determine the dilatational and shear moduli weevaluated the response of pure peptide monolayers to an oscillatory anisotropiccompressive work. Additionally, a micro-rheological characterization wasperformed by tracking the diffusion of micrometer sized latex beads onto theinterface. This technique allowed us the detection of different rheologicalbehaviour between monolayers presenting a low shear response. Monolayers of theb-sheet structure-adopting peptides, suchas b-amyloid peptides, exhibited a markedshear (elastic) modulus even at low surface pressures. In contrast, Melmonolayers exhibited negligible shear modulus and the micro-rheological shearresponse was markedly lower than that observed for either Ab1-40 or Ab1-42 amyloid peptides.When Mel monolayers where formed at the interface of an aqueous solution at pH11, we observed an increase in both the lateral stability and film viscosity asdetected by a slower diffusion of the latex beads, in keeping with an increasein b-sheet structure at this high pH (verifiedby ATR and FT-IR measurements). We suggest that the interactions responsiblefor the marked response upon shear observed for b-amyloidpeptide monolayers are the hydrogen bonds of the b-sheetstructure that can form an infinite planar network at the interface.Conversely, a-helical Mel peptide lack of theseinter-molecular interactions and, therefore the shear contribution was negligible.We propose that the secondary structure isimportant for modulating the rheological behavior ofshort peptide monolayers regardless of the mass density or surfacecharge at the surface.