Speaker
Chris Miranda
(Memorial University of Newfoundland)
Description
Transfer of lipid material between mulitlamellar reservoirs and the surface active layer is required to maintain the functional surfactant layer in alveoli. Surfactant Protein B (SP-B) is believed to facilitate interlayer contact implicit in such activity. The way in which SP-B might promote trafficking of surfactant material was investigated using mixtures bilayered micelles containing long- and short- chain lipids. Because of their propensity to progressively coalesce into more extended bilayer structures on heating, bicellar mixture suspensions provide interesting systems to study peptide-induced interaction between lipid structures. 2H NMR was used to study the effect of an SP-B fragment (SP-B63-78), at 10% (w/w), on the coalescence behaviour of three bicellar mixtures: DMPC-d54/DMPC/DHPC (3:1:1); DMPC-d54/DMPG/DHPC (3.33:0.67:1); and DMPC-d54/DMPG/DHPC (3:1:1). In bicellar mixtures containing only zwitterionic lipids (DMPC-d54/DMPC/DHPC), the peptide had no effect on the temperatures at which transitions to more extended structures occurred. Conversely, in bicellar mixtures containing anionic lipids (DMPC-d54/DMPG/DHPC), addition of the peptide was found to reduce the temperature at which the magnetically-orientable bicellar ribbon phase was replaced by more extended lamellar structures. This peptide-induced perturbation of bicellar mixture phase behaviour increased with anionic lipid concentration. Comparisons with spectra obtained from DMPC/DMPG-d54/DHPC (3:1:1) and DMPC-d54/DMPG/DHPC (3:1:1) mixtures showed that DMPC and DMPG occupy similar environments in these mixtures both in the presence and absence of the peptide. These results indicate the interaction of SP-B63-78 with lipid structures depends on the presence of anionic lipids and that the mechanism by which SP-B63-78 interacts with bicelles does not involve a separation of anionic and zwitterionic long-chain lipids.
Author
Chris Miranda
(Memorial University of Newfoundland)
Co-authors
Michael Morrow
(Memorial University of Newfoundland)
Valerie Booth
(Memorial University of Newfoundland)
