title: SP-A permeabilizes lipopolysaccharide membranes by forming protein aggregates that extract lipids from the membrane.
abstract: Surfactant protein A (SP-A) is known to cause bacterial permeabilization. The aim of this work was to gain insight into the mechanism by which SP-A induces permeabilization of rough lipopolysaccharide (Re-LPS) membranes. In the presence of calcium, large interconnected aggregates of fluorescently labeled TR-SP-A were observed on the surface of Re-LPS films by epifluorescence microscopy. Using Re-LPS monolayer relaxation experiments at constant surface pressure, we demonstrated that SP-A induced Re-LPS molecular loss by promoting the formation of three-dimensional lipid-protein aggregates in Re-LPS membranes. This resulted in decreased van der Waals interactions between Re-LPS acyl chains, as determined by differential scanning calorimetry, which rendered the membrane leaky. We also showed that the coexistence of gel and fluid lipid phases within the Re-LPS membrane conferred susceptibility to SP-A-mediated permeabilization. Taken together, our results seem to indicate that the calcium-dependent permeabilization of Re-LPS membranes by SP-A is related to the extraction of LPS molecules from the membrane due to the formation of calcium-mediated protein aggregates that contain LPS.
authors.affiliation: Department of Biochemistry and Molecular Biology I, Complutense University of Madrid, Madrid, Spain.
authors.forename: Olga
authors.initials: O
authors.lastname: Cañadas
authors.forename: Ignacio
authors.initials: I
authors.lastname: García-Verdugo
authors.forename: Kevin M W
authors.initials: KM
authors.lastname: Keough
authors.forename: Cristina
authors.initials: C
authors.lastname: Casals
mesh_terms: D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects*; D006090:Gram-Negative Bacteria / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism; D008070:Lipopolysaccharides / Q000302:isolation & purification* / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D037662:Pulmonary Surfactant-Associated Protein A / Q000378:metabolism* / Q000494:pharmacology*; D013499:Surface Properties; D014867:Water / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D008070:Lipopolysaccharides; D037662:Pulmonary Surfactant-Associated Protein A; D014867:Water; D002118:Calcium