| Popis: |
In vitro studies of pulmonary surfactant peptides in vesicles of mixed lipid composition are examined using nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and fluorescence spectroscopy. As KL4, a 21 residue mimetic of surfactant protein B (SP-B), has been used to restore lung compliance and promote gaseous exchange in premature babies with respiratory distress syndrome (RDS); and has served as a model in elucidating the mechanism by which lipids are trafficked to and from the air-fluid interface of alveoli. Here we utilize a pyrene phospholipid analog to investigate the effect of KL4 on lipid organization and acyl chain dynamics by monitoring changes in excimer-to-monomer (Ie/Im) ratio. This experiment probes the environment of the hydrophobic core of DPPC/POPG and POPC/POPG liposomes. An average decrease of ∼27-40% and ∼0-10% in Ie/Im was observed in the DPPC/POPG and POPC/POPG LUVs, respectively, with increasing peptide concentration (0.5 to 5 mol%). This decrease is directly proportional to a lowered probability of excimer formation, which is highly dependent on proximal interactions of an excited monomer with a pyrene moiety at ground state. The ability of the peptide to modify membrane fluidity properties was studied via anisotropy measurements of a rhodamine-labeled phospholipid. A steady increase in the order was observed in the DPPC/POPG liposomes with relatively constant fluorescence intensity, while collisional quenching was observed in the POPC/POPG liposomes. Further studies were performed on the SP-B N and C-terminal constructs for correlation with NMR and EPR observations, and proposed mechanisms of peptide-mediated lipid trafficking. |
