The L_γ Phase of Pulmonary Surfactant

Abstract

To determine how different components affect the structure of pulmonary surfactant, we measured X-ray scattering by samples derived from calf surfactant. The surfactant phospholipids demonstrated the essential characteristics of the L phase: a unit cell with a lattice constant appropriate for two bilayers, and crystalline chains detected by wide-angle X-ray scattering (WAXS). The electron density profile, obtained from scattering by oriented films at different relative humidities (70-97%), showed that the two bilayers, arranged as mirror images, each contain two distinct leaflets with different thicknesses and profiles. The detailed structures suggest one ordered leaflet that would contain crystalline chains and one disordered monolayer likely to contain the anionic compounds, which constitute ∼10% of the surfactant phospholipids. The spacing and temperature dependence detected by WAXS fit with an ordered leaflet composed of dipalmitoyl phosphatidylcholine. Physiological levels of cholesterol had no effect on this structure. Removing the anionic phospholipids prevented formation of the L phase. The cationic surfactant proteins inhibited L structures, but at levels unlikely related to charge. Because the L phase, if arranged properly, could produce a self-assembled ordered interfacial monolayer, the structure could have important functional consequences. Physiological levels of the proteins, however, inhibit formation of the L structures at high relative humidities, making their physiological significance uncertain.

Structure and Thermotropic Behavior of Bovine- and Porcine-Derived Exogenous Lung Surfactants

“…In the remaining regions, we only see L α (red ★), as in Curosurf. WAXS data obtained for suspensions of calf lung surfactant extract (CLSE) showed a broad peak (between 1.4 and 1.5 Å −1 ) superimposed on another sharp peak (at 1.5 Å −1 ) that diminished with heating and then vanished, with only the broad one at the position around 1.4 Å −1 remaining, 44 consistent with our observations, even if CLSE, bovine-derived, is obtained from bronchoalveolar lavage.…”

The Impact of Nonequilibrium Conditions in Lung Surfactant: Structure and Composition Gradients in Multilamellar Films

“…Interestingly, similar SAXS patterns have later also been reported for natural lung surfactant extracts with similarities to Curosurf. 48 − 50 A similar scattering pattern was recently also reported for mixed phospholipid vesicles in the presence of peptides. 51 The formation mechanism of such an original lamellar structure likely originates from protein/lamellae interactions, for instance, through anchoring or bridging.…”

Suppression of Lα/Lβ Phase Coexistence in the Lipids of Pulmonary Surfactant

“…Concentrations of the proteins and phospholipids were determined by colorimetric assays (30,31), using bovine serum albumin as the standard protein. The content of the proteins (32), their physical constants (Table 1), and the composition of the lipids (16,27,34,35) in CLSE are all known. SP-B and SP-C represent $1.5% (w/w) ($500:1 lipid/ protein molar ratio) of the complete mixture (32).…”

“…The content of the proteins (32), their physical constants (Table 1), and the composition of the lipids (16,27,34,35) in CLSE are all known. SP-B and SP-C represent $1.5% (w/w) ($500:1 lipid/ protein molar ratio) of the complete mixture (32).…”