title: An amino-terminal amphipathic alpha-helix mediates membrane association of the hepatitis C virus nonstructural protein 5A.
abstract: Hepatitis C virus (HCV) nonstructural protein 5A (NS5A), a phosphoprotein of unknown function, is believed to be a component of a membrane-associated viral replication complex. The determinants for membrane association of NS5A, however, have not been defined. By double label immunofluorescence analyses, NS5A was found to be associated with the endoplasmic reticulum (ER) or an ER-derived modified compartment both when expressed alone or in the context of the entire HCV polyprotein. Systematic deletion and green fluorescent protein fusion analyses allowed us to map the membrane anchor to the amino-terminal 30 amino acid residues of NS5A. Membrane association occurred by a posttranslational mechanism and resulted in properties of an integral membrane protein. Circular dichroism structural studies of a synthetic peptide corresponding to the NS5A membrane anchor, designated NS5A(1-31), demonstrated the presence of an amphipathic alpha-helix that was found to be highly conserved among 280 HCV isolates of various genotypes. The detergent-binding properties of this helical peptide together with the nature and location of its amino acids suggest a mechanism of membrane insertion via the helix hydrophobic side, yielding a topology parallel to the lipid bilayer in the cytoplasmic leaflet of the ER membrane. These findings have important implications for the structural and functional organization of the HCV replication complex and may define novel targets for antiviral intervention.
authors.affiliation: Department of Medicine II, University of Freiburg, D-79106 Freiburg, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Brass
authors.forename: Elke
authors.initials: E
authors.lastname: Bieck
authors.forename: Roland
authors.initials: R
authors.lastname: Montserret
authors.forename: Benno
authors.initials: B
authors.lastname: Wölk
authors.forename: Jan Albert
authors.initials: JA
authors.lastname: Hellings
authors.forename: Hubert E
authors.initials: HE
authors.lastname: Blum
authors.forename: François
authors.initials: F
authors.lastname: Penin
authors.forename: Darius
authors.initials: D
authors.lastname: Moradpour
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003902:Detergents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005838:Genotype; D049452:Green Fluorescent Proteins; D006801:Humans; D008055:Lipids / Q000737:chemistry; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D013752:Tetracycline / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection; D017361:Viral Nonstructural Proteins / Q000737:chemistry* / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase
chemical_list: D000596:Amino Acids; D003902:Detergents; D049452:Green Fluorescent Proteins; D008055:Lipids; D008164:Luminescent Proteins; D010455:Peptides; D011500:Protein Synthesis Inhibitors; D011993:Recombinant Fusion Proteins; D013752:Tetracycline; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase