title: Fluorescently labeled pulmonary surfactant protein C in spread phospholipid monolayers.
abstract: Pulmonary surfactant, a lipid-protein complex, secreted into the fluid lining of lungs prevents alveolar collapse at low lung volumes. Pulmonary surfactant protein C (SP-C), an acylated, hydrophobic, alpha-helical peptide, enhances the surface activity of pulmonary surfactant lipids. Fluorescein-labeled SP-C (F-SP-C) (3, 6, 12 wt%) in dipalmitoylphosphatidylcholine (DPPC), and DPPC:dipalmitoylphosphatidylglycerol (DPPG) [DPPC:DPPG 7:3 mol/mol] in spread monolayers was studied by epifluorescence microscopy. Mass spectometry of F-SP-C indicated that the protein is partially deacylated and labeled with 1 mol fluorescein/1 mol protein. The protein partitioned into the fluid, or liquid expanded, phase. Increasing amounts of F-SP-C in DPPC or DPPC:DPPG monolayers decreased the size and total amounts of the condensed phase at all surface pressures. Calcium (1.6 mM) increased the amount of the condensed phase in monolayers of DPPC:DPPG but not of DPPC alone, and such monolayers were also perturbed by F-SP-C. The study indicates that SP-C perturbs the packing of neutral and anionic phospholipid monolayers even when the latter systems are condensed by calcium, indicating that interactions between SP-C and the lipids are predominantly hydrophobic in nature.
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Nag
authors.forename: J
authors.initials: J
authors.lastname: Perez-Gil
authors.forename: A
authors.initials: A
authors.lastname: Cruz
authors.forename: K M
authors.initials: KM
authors.lastname: Keough
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000737:chemistry; D003460:Crystallization; D016650:Fluorescein-5-isothiocyanate; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry; D008560:Membrane Fluidity; D008567:Membranes, Artificial; D008856:Microscopy, Fluorescence; D010715:Phosphatidylglycerols / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry; D017433:Protein Structure, Secondary; D011510:Proteolipids / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013499:Surface Properties; D013552:Swine; D013816:Thermodynamics
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D015060:1,2-Dipalmitoylphosphatidylcholine; D016650:Fluorescein-5-isothiocyanate; D002118:Calcium; C030345:1,2-dipalmitoylphosphatidylglycerol