title: Lysophospholipids prevent binding of a cytolytic protein ostreolysin to cholesterol-enriched membrane domains.
abstract: Ostreolysin, a 15kDa pore-forming protein from the oyster mushroom (Pleurotus ostreatus), binds specifically to cholesterol-enriched membrane domains existing in the liquid-ordered phase, and lyses cells and lipid vesicles made of cholesterol and sphingomyelin. We have monitored binding of sub-lytic concentrations of ostreolysin to membranes of Chinese Hamster Ovary cells and rat somatotrophs, using primary anti-ostreolysin and fluorescence-labeled secondary antibodies detected by confocal microscopy. Depletion of more than 40% membrane cholesterol content by methyl-beta-cyclodextrin dramatically decreased ostreolysin binding. Immunostaining showed that ostreolysin is not co-localized with raft-binding proteins, cholera toxin B-subunit or caveolin, suggesting that natural membranes display heterogeneity of cholesterol-enriched raft-like microdomains. Impaired ostreolysin binding was also observed after treating the cells with lysophosphatidylinositol. Effects of lysophosphatidylinositol on binding of ostreolysin to immobilized large sphingomyelin/cholesterol (1/1, mol/mol) unilamellar vesicles were studied by a surface plasmon resonance technique. Injection of ostreolysin during the lysophosphatidylinositol dissociation phase showed an inverse relationship between ostreolysin binding and the quantity of lysophosphatidylinositol in the membranes of lipid vesicles. It was concluded that lysophospholipids prevent binding of ostreolysin to cell and to artificial lipid membranes resembling lipid rafts, by partitioning into the lipid bilayer and altering the properties of cholesterol-rich microdomains.
authors.affiliation: Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, Institute of Pathophysiology, Slovenia & Celica Biomedical Center, University of Ljubljana, Proletarska 4, Ljubljana, Slovenia.
authors.forename: Helena H
authors.initials: HH
authors.lastname: Chowdhury
authors.forename: Katja
authors.initials: K
authors.lastname: Rebolj
authors.forename: Marko
authors.initials: M
authors.lastname: Kreft
authors.forename: Robert
authors.initials: R
authors.lastname: Zorec
authors.forename: Peter
authors.initials: P
authors.lastname: Macek
authors.forename: Kristina
authors.initials: K
authors.lastname: Sepcić
mesh_terms: D000818:Animals; D016466:CHO Cells; D002463:Cell Membrane Permeability / Q000187:drug effects; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D005656:Fungal Proteins / Q000378:metabolism; D006460:Hemolysin Proteins / Q000378:metabolism*; D008246:Lysophospholipids / Q000494:pharmacology*; D008297:Male; D021962:Membrane Microdomains / Q000378:metabolism*; D008567:Membranes, Artificial; D051379:Mice; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D005656:Fungal Proteins; D006460:Hemolysin Proteins; D008246:Lysophospholipids; D008567:Membranes, Artificial; D047392:beta-Cyclodextrins; C025449:lysophosphatidylinositol; C108732:methyl-beta-cyclodextrin; C461280:ostreolysin; D002784:Cholesterol