title: High-density rafts preferentially host the complement activator measles virus F glycoprotein but not the regulators of complement activation.
abstract: The fusion (F) protein of measles virus (MeV) activates the alternative pathway of human complement in the presence of both CD46 and CD55 which regulate the complement activation [Devaux, P., Christiansen, D., Plumet, S., Gerlier, D., 2004. Cell surface activation of the alternative complement pathway by the fusion protein of measles virus. J. Gen. Virol. 85, 1665-1673]. The original observation of cold detergent-resistant membranes sedimenting at a higher density than the membrane rafts lead us to analyse the respective distribution of F, CD46 and C55 molecules in what we call heavy rafts (HRs) and in the classical low-density membrane rafts (Rs). Membrane rafts were isolated after cold TX100 solubilization and flotation on a sucrose gradient. The denser fractions collected from the lower part of the gradient could be further separated into a translucent pellet (HR) and a soluble supernatant (S). HR and R were both sensitive to TX100 solubilization after cholesterol depletion and solubilized by octyl-d-glucoside but differed in their lipid and protein composition. A proteomic analysis revealed that the HR fraction was derived from heterogeneous cellular membranes including plasma membrane, early endosomes and rough endoplasmic reticulum. Interestingly, CD55 and CD46 almost exclusively associated with R and S fractions, respectively, while after MeV infection or transient expression, MeV-F distributed almost equally between R, HR and S fractions. However more immature MeV-F(0) than mature MeV-F(1) proteins was associated with the HR fraction whereas this ratio was reverse in R and S fractions. After activation of the alternative pathway of human complement by F expressing cells, both C3b and F protein associated with R, HR and S fractions. When four or five of the five cysteines located in the transmembrane and cytoplasmic tail of F protein were substituted with serine residues, the mutated F distributed almost exclusively in HR fractions and was still efficient in activating the complement. We propose that the partitioning of F, CD46 and CD55 molecules in different membrane microdomains could account for the ability of F to escape complement regulation by the CD55 and CD46 regulators.
authors.affiliation: Virus-Host Cell Interaction, Université Lyon 1, CNRS, FRE 3011, IFR 62 Lyon-Est, 69372 Lyon Cedex 08, France.
authors.forename: Arije
authors.initials: A
authors.lastname: Ghannam
authors.forename: Djilali
authors.initials: D
authors.lastname: Hammache
authors.forename: Christel
authors.initials: C
authors.lastname: Matias
authors.forename: Mathilde
authors.initials: M
authors.lastname: Louwagie
authors.forename: Jérôme
authors.initials: J
authors.lastname: Garin
authors.forename: Denis
authors.initials: D
authors.lastname: Gerlier
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D018958:CD55 Antigens / Q000276:immunology; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D003167:Complement Activation / Q000187:drug effects / Q000276:immunology*; D003176:Complement C3 / Q000276:immunology; D003170:Complement Pathway, Alternative / Q000187:drug effects / Q000276:immunology; D003545:Cysteine / Q000235:genetics; D006017:Glycolipids / Q000378:metabolism; D006801:Humans; D008459:Measles virus / Q000187:drug effects / Q000276:immunology*; D051916:Membrane Cofactor Protein / Q000276:immunology; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D017830:Octoxynol / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D040901:Proteomics; D013347:Subcellular Fractions / Q000187:drug effects; D014760:Viral Fusion Proteins / Q000737:chemistry / Q000276:immunology*
chemical_list: D018958:CD55 Antigens; D003176:Complement C3; D006017:Glycolipids; D051916:Membrane Cofactor Protein; D014760:Viral Fusion Proteins; D017830:Octoxynol; D002784:Cholesterol; D003545:Cysteine