The hydrophobic surfactant proteins SP-B and SP-C promote rapid adsorption of pulmonary surfactant to an air/water interface. Previous evidence suggests that they achieve this effect by facilitating the formation of a rate-limiting negatively curved stalk between the vesicular bilayer and the interface. To determine whether the proteins can alter the curvature of lipid leaflets, we used x-ray diffraction to investigate how the physiological mixture of these proteins affects structures formed by 1-palmitoyl-2-oleoyl phosphatidylethanolamine, which by itself undergoes the lamellar-to-inverse hexagonal phase transition at 71 degrees C. In amounts as low as 0.03% (w:w) and at temperatures as low as 57 degrees C, the proteins induce formation of bicontinuous inverse cubic phases. The proteins produce a dose-related shift of diffracted intensity to the cubic phases, with minimal evidence of other structures above 0.1% and 62 degrees C, but no change in the lattice-constants of the lamellar or cubic phases. The induction of the bicontinuous cubic phases, in which the individual lipid leaflets have the same saddle-shaped curvature as the hypothetical stalk-intermediate, supports the proposed model of how the surfactant proteins promote adsorption.

No abstract

No abstract

peptide to membranes that also contain the channel-forming peptide gramicidin A allowed us to observe the membrane adsorption of A1AT. The protein interacts with the channel and produces transient current interruptions. The on-rate of these events depends non-linearly on the A1AT concentration and scales with the mole percentage of the charged lipid in the membrane. The measured off-rate is surface-charge independent. Thus, our results suggest that the membrane lipid composition plays an important regulatory role in the physiological activity of the A1AT and its interaction with the membrane.

No abstract