Effect of Hydrophobic Surfactant Peptides SP-B and SP-C on Binary Phospholipid Monolayers. I. Fluorescence and Dark-Field Microscopy

Abstract

The influence of the hydrophobic proteins SP-B and SP-C, isolated from pulmonary surfactant, on the morphology of binary monomolecular lipid films containing phosphocholine and phosphoglycerol (DPPC and DPPG) at the air-water interface has been studied using epifluorescence and dark-field microscopy. In contrast to previously published studies, the monolayer experiments used the entire hydrophobic surfactant protein fraction (containing both the SP-B and SP-C peptides) at physiologically relevant concentrations (approximately 1 wt %). Even at such low levels, the SP-B/C peptides induce the formation of a new phase in the surface monolayer that is of lower intrinsic order than the liquid condensed (LC) phase that forms in the pure lipid mixture. This presumably leads to a higher structural flexibility of the surface monolayer at high lateral pressure. Variation of the subphase pH indicates that electrostatic interaction dominates the association of the SP-B/C peptides with the lipid monolayer. As evidenced from dark-field microscopy, monolayer material is excluded from the DPPC/DPPG surface film on compression and forms three-dimensional, surface-associated structures of micron dimensions. Such exclusion bodies formed only with SP-B/C peptides. This observation provides the first direct optical evidence for the squeeze-out of pulmonary surfactant material in situ at the air-water interface upon increasing monolayer surface pressures.

Roles of γ-Globulin in the Dynamic Interfacial Behavior of Mixed Dipalmitoyl Phosphatidylcholine/γ-Globulin Monolayers at Air/Liquid Interfaces

“…Thus, a possible interfacial role for SP-B and SP-C in lipid replenishment through enhancement of the respreading of DPPC collapse phases or through reversible removal of phospholipids during dynamic compression-expansion of the interface has been proposed (14,15). Moreover, the results obtained by epifluorescence and dark-field microscopy provided evidence that SP-B and SP-C acted in softening the lipids, presumably essential for a high structural flexibility of the monolayer at higher lateral pressures, and were involved in surface refinement by means of squeeze-out of monolayer materials upon compression (22). However, during rapid cyclic area changes, it has been suggested that SP-B and SP-C remained associated with the surface film (23).…”

A study of HIV-1 FP inhibition by GBV-C peptides using lipid nano-assemblies

“…The magnified image in the inset shows dark green areas corresponding to an LC phase; this ordered phase is probably dissolved down to a micron-sized grain. This phenomenon has been described for surfactant peptides and alamethicin when they interact with negative charged monolayers [32][33][34]. A possible explanation is some new phase that better dissolves the lipophilic dye, and is hence presumably of lower intrinsic order.…”

Structural investigation on the adsorption of the MARCKS peptide on anionic lipid monolayers – effects beyond electrostatic

“…Surface pressure-area isotherms of the monolayers were obtained using a thermostated Langmuir film balance of home made design (Dyck and Lösche, 2006) at a subphase temperature of 20 • C. The studies of the mesoscopic morphology of the monolayer were performed with a Zeiss Axiotech Vario epifluorescence microscope (dye NBD C 12 -HPC, Molecular Probes, Leiden, The Netherlands), associated with the film balance (Krüger et al, 1999) The dissolved DPPC and the DPPC/DPPS mixtures were spread on the subphase and the solvent was allowed to evaporate for at least 10 min. The monolayers were compressed typically at a barrier speed that corresponded to approximately 2 Å 2 /(molecule min) and the surface pressure was monitored continuously.…”