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Lipids, Pulmonary surfactant, Pulmonary surfactant -- Metabolism


Prior studies have shown that the biological mixture of the two hydrophobic surfactant proteins, SP-B and SP-C, produces faster adsorption of the surfactant lipids to an air/water interface, and that they induce 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) to form inverse bicontinuous cubic phases. SP-B has a much greater effect than SP-C on adsorption. If the two proteins induce formation of the bicontinuous structures and faster adsorption by similar mechanisms, then they should also have differential ability to form the cubic phases. To test this hypothesis, we measured small angle X-ray scattering on the individual proteins combined with POPE. SP-B replicated the doserelated ability of the combined proteins to induce the cubic phases at temperatures more than 25°C below the point at which POPE alone forms the curved inverse-hexagonal phase. With SP-C, diffraction from cubic structures was either absent or present only with larger amounts of protein at low intensities. The correlation between the structural effects of inducing curved structures and the functional effects on the rate of adsorption fits with the model in which SP-B promotes adsorption by facilitating formation of a negatively curved, rate-limiting intermediate structure.


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