title: Interactions of pulmonary surfactant protein A with phospholipid monolayers change with pH.
abstract: The interaction of pulmonary surfactant protein A (SP-A) labeled with Texas Red (TR-SP-A) with monolayers containing zwitterionic and acidic phospholipids has been studied at pH 7.4 and 4.5 using epifluorescence microscopy. At pH 7.4, TR-SP-A expanded the pi-A isotherms of film of dipalmitoylphosphatidylcholine (DPPC). It interacted at high concentration at the edges of condensed-expanded phase domains, and distributed evenly at lower concentration into the fluid phase with increasing pressure. At pH 4.5, TR-SP-A expanded DPPC monolayers to a slightly lower extent than at pH 7.4. It interacted primarily at the phase boundaries but it did not distribute into the fluid phase with increasing pressure. Films of DPPC/dipalmitoylphosphatidylglycerol (DPPG) 7:3 mol/mol were somewhat expanded by TR-SP-A at pH 7.4. The protein was distributed in aggregates only at the condensed-expanded phase boundaries at all surface pressures. At pH 4.5 TR-SP-A caused no expansion of the pi-A isotherm of DPPC/DPPG, but its fluorescence was relatively homogeneously distributed throughout the expanded phase at all pressures studied. These observations can be explained by a combination of factors including the preference for SP-A aggregates to enter monolayers at packing dislocations and their disaggregation in the presence of lipid under increasing pressure, together with the influence of pH on the aggregation state of SP-A and the interaction of SP-A with zwitterionic and acidic lipid.
authors.affiliation: Departamento de Bioquímica, Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain.
authors.forename: M L
authors.initials: ML
authors.lastname: Ruano
authors.forename: K
authors.initials: K
authors.lastname: Nag
authors.forename: C
authors.initials: C
authors.lastname: Casals
authors.forename: J
authors.initials: J
authors.lastname: Pérez-Gil
authors.forename: K M
authors.initials: KM
authors.lastname: Keough
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000737:chemistry*; D008856:Microscopy, Fluorescence / Q000379:methods; D010715:Phosphatidylglycerols / Q000737:chemistry*; D011510:Proteolipids / Q000737:chemistry* / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000737:chemistry* / Q000378:metabolism*; D013552:Swine; D014966:Xanthenes
chemical_list: D005456:Fluorescent Dyes; D008081:Liposomes; D010715:Phosphatidylglycerols; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D014966:Xanthenes; D015060:1,2-Dipalmitoylphosphatidylcholine; C034657:Texas red; C030345:1,2-dipalmitoylphosphatidylglycerol