Microstructure and dynamic surface properties of surfactant protein SP-B/dipalmitoylphosphatidylcholine interfacial films spread from lipid-protein bilayers.
Suspensions of dipalmitoylphosphatidylcholine (DPPC) bilayers containing 5, 10 or 20% (w/w) surfactant protein SP-B have been reconstituted and spread at air-liquid interfaces. Compression isotherms of DPPC/SP-B monolayers spread from these preparations were qualitatively comparable to the isotherms of the corresponding DPPC/SP-B monolayers spread from solvents. SP-B was squeezed-out at higher pressures from vesicle-spread films than from solvent-spread monolayers. SP-B caused a marked decrease on the rate of relaxation of DPPC collapse phases to equilibrium pressures in all the lipid/protein films assayed. This stabilizing effect was higher in vesicle-spread than in solvent-spread monolayers. Inclusion in the films of traces of the fluorescent probe NBD-PC (1 mol%) and use of a fluorescent derivative of SP-B labeled with a rhodamine derivative, Texas Red, allowed for direct observation of protein and lipid domains at the interface by epifluorescence microscopy. Upon compression, SP-B altered the packing of phospholipids in the bilayer-spread films, observed as a SP-B-induced reduction of the area of liquid-condensed domains, in a way similar to its effect in solvent-spread monolayers. SP-B was not associated with condensed regions of the films. Fluorescence images from vesicle-spread films showed discrete fluorescent aggregates that could be consistent with the existence of lipid-protein vesicles in close association with the monolayer. Both the retention of SP-B at higher surface pressures and the greater stability of collapse phases of DPPC/SP-B films prepared by spreading from liposomes in comparison to those spread from solvents can be interpreted as a consequence of formation of complex bilayer-monolayer interacting systems.
Cruz
A
A
Departamento de Bioquimica, Facultad de Biología, Universidad Complutense, Madrid, Spain.
Worthman
L A
LA
Serrano
A G
AG
Casals
C
C
Keough
K M
KM
Pérez-Gil
J
J
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000327:Adsorption; D001703:Biophysics / Q000379:methods; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
D008051:Lipid Bilayers; D013501:Surface-Active Agents; D015060:1,2-Dipalmitoylphosphatidylcholine