Ramos-Torres, Sindia

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    Surfactant Protein C analogues and model lipid interactions in lung surfactant
    (2006) Ramos-Torres, Sindia; Pastrana-Ríos, Belinda; College of Arts and Sciencies - Sciences; Vera-Colón, Marisol; Ríos-Steiner, Jorge; Department of Chemistry; Ríos-Velázquez, Carlos
    Lung surfactant is a mixture of lipids and proteins that stabilizes the respiratory surface of lungs against collapse. Deficiency in its amount or composition is related to severe respiratory disorders. Exogenous-surfactant treatment has proven to be highly effective for improved oxygen index, increased lung compliance and thus, reduce the work of breathing. Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) were successfully applied to study ternary mixtures of native Surfactant Protein C (SP-C), modified SP-C (mSP-C) or T₁₁ peptoid in a model lipid mixture of DPPC-𝘥₆₂/DPPG (7:1 mol/mol). The secondary structure of the SP-C analogues, the orientation of α-helical segments relative to the bilayer normal in membrane films and their effect in the thermotropic properties of lipid multillamelar vesicles were determined. Modified SP-C was found to predominantly possess α-helical secondary structure as native SP-C. The helical segments of mSP-C and SP-C exhibited a parallel orientation with respect to the membrane normal. Only ~25 % of exchangeable protons were observed to exchange in D₂O, which reflects the hydrophobic nature of both molecules. However, T₁₁ is comprised of multiple conformations, which require further analysis by FT-IR. In addition, T₁₁ produced smaller effects on the thermotropic properties of the lipidic environment, as measured from acyl chain CH₂ and CD₂ antisymmetric and lipid carbonyl stretching frequencies. The van’t Hoff enthalpies were also determined by both techniques. The obtained results were used to evaluate the synthetic peptide candidates for lung surfactant replacement therapy.