Acylation of Pulmonary Surfactant Protein-C Is Required for Its Optimal Surface Active Interactions with Phospholipids

Abstract

This study investigates the importance of thioesterlinked acyl groups in lung surfactant protein C (SP-C) in facilitating interactions with phospholipids that yield functionally important surface active behaviors. Native SP-C, palmitoylated at cysteine residues at positions 5 and 6, was isolated from bovine lung surfactant by liquid chromatography.

Synthetic Surfactant Protein Analogues

“…Preliminary results from analysis of dipalmitoylated SP-C(Leu) studied in the captive bubble surfactometer show that the palmitoyl groups influence the biophysical properties [Schürch S, Gustafsson M, et al, unpublished data]. This confirms the results from analysis of depalmitoylated SP-C [12,13] and indicates that the latter results are not likely to be due to the effects of the depalmitoylation procedure used and concomitant reduction in helical content.…”

“…The palmitoylcysteines at positions 5 and 6 of SP-C appear to be important both for the integrity of the ·-helical structure and for functional properties. Chemical depalmitoylation of SP-C gives a reduction of about 20% in the ·-helical content, largely independent of the environment used for analysis [7,11,12]. The reasons for Johansson/Gustafsson/Palmblad/ Zaltash/Robertson/Curstedt this remain to be resolved.…”

“…One possibility is that one or both of the palmitoyl groups form hydrogen bonds with the amide protons of the first helical turn, which otherwise would remain unprotected, and thereby stabilize the helix. Chemical depalmitoylation also leads to retarded adsorption and respreading of phospholipids at an air/water interface, reduced mechanical stability of the interfacial film, and inferior surface tension-lowering properties during surface compression [12,13]. This indicates that palmitoylation is essential for the optimal surface activity of SP-C.…”

The murine SP-C promoter directs type II cell-specific expression in transgenic mice

“…A synthetic replacement surfactant consisting of surfactant phospholipids supplemented with a recombinant SP-C peptide as the only protein component restores pulmonary function in several animal models of surfactant-depleted acute lung injury (11). Addition of purified SP-C to synthetic phospholipid preparations lowers the surface activity to levels approximating whole native surfactant preparations (24).…”

Selective Labeling of Pulmonary Surfactant Protein SP-C in Organic Solution

“…All the spectra are dominated by the ␣-helical contribution to the secondary structure which was around 60% for the two proteins in LPC and about 70% in phospholipid vesicles, as previously reported (28). The labeling reaction has not therefore perturbed the overall conformation of the protein, which is very sensitive to environmental perturbations during manipulation such as changes in solvent polarity, pH, or protein concentration (5,18,34), but also to chemical deacylation (5,35). Dans-SP-C also conserves the ability of the native protein to promote interfacial adsorption of phospholipids, as seen in Fig.…”