Abstract
In this thesis, the interaction of four kinds of peptides,CV-25 (similar to viral peptides), CK-25, CS-28 (similar to Magainin 2), and CQ-31 (similar to Melittin), with the lipid bilayer or monolayer were investigated. Fist, the interaction with the lipid monolayer formed at the air-water interface was investigated by measuring the isotherm with a Langmuir-Blodgett trough. The peptide concentration in the sub-phase was varied 0.05 μM ~ 5 μM. he monolayer films in together with the adsorbed peptides were transferred to silicon wafer and checked by X-ray reflectivity and atomic force microscopy. The CK-25 peptide is highly hydrophilic and positively charged. Except CK-25 peptide, the interaction of the other three kinds of peptides with mixed DPPC and DPPG (molar ratio is 3 to 1), DOPC and DOPG(molar ratio is 3 to 1), POPC and POPG (molar ratio is 3 to 1) monolayer are concentration dependent. For the CK-25, it does not insert into the monolayer but can be adsorbed to the monolayer head group layer. When the concentration of CV-25 (viral peptide) increases from 0.1 μM to 2.5 μM for interacting with the 25% DPPG monolayer maintained at the surface pressure 20mN/m, the surface area per lipid molecule increases by 7% and 16%, respectively. For CS-28 peptide, the surface area expansion is 13% at 0.1 μM, 58% at 0.25 μM, and continues to expand at 0.5 μM and 2.5 μM. As for the CQ-28 peptide, the surface area expands continuously at above 0.1 μM (no expansion at 0.05 μM). iv For studying the interaction with lipid bilayer, we have prepared the unilamellar vesicles and the lipid bicelles (mixing with long-chain lipids with short-chain lipids at the ratio of 3 to 1). For the 25% DPPG bicelles, in the presence of CV-25 (viral peptide), the thickness of the lipid headgroup layer becomes thinner as the peptide concentration increases. When the peptide concentration is increased to 5wt%, the 25% DPPG bicelles begin to show stacking as revealed by small-angle X-ray scattering. The addition of the CK-25 peptide to the 25% DPPG bicelles would induce the stacking of the bicelles to form one-dimensionally stacked lamellar structure with a d-spacing of 6.7 nm. In the presence of CS-28 (Magainin 2) peptides, the hydrophilic headgroup layer would become slightly thicker. The addition of CQ-31 (Melittin), the bilayer hydrocarbon (tails) layer would become thinner for the 25% DPPG bicelles and it would also induce some bicelle aggregation. For the interaction with 25% DPPG vesicles, the addition of CK 25 would induce the formation of multilamellar liposomes. As for the addition of CS-28 (Magainin 2), hydrophilic head layer of 25% DPPG vesicle would become slightly thicker and the addition of CQ-31 (Melittin) also has the similar effect.