title: Insertion and topology of a plant viral movement protein in the endoplasmic reticulum membrane.
abstract: Virus-encoded movement proteins (MPs) mediate cell-to-cell spread of viral RNA through plant membranous intercellular connections, the plasmodesmata. The molecular pathway by which MPs interact with viral genomes and target plasmodesmata channels is largely unknown. The 9-kDa MP from carnation mottle carmovirus (CarMV) contains two potential transmembrane domains. To explore the possibility that this protein is in fact an intrinsic membrane protein, we have investigated its insertion into the endoplasmic reticulum membrane. By using in vitro translation in the presence of dog pancreas microsomes, we demonstrate that CarMV p9 inserts into the endoplasmic reticulum without the aid of any additional viral or plant host components. We further show that the membrane topology of CarMV p9 is N(cyt)-C(cyt) (N and C termini of the protein facing the cytoplasm) by in vitro translation of a series of truncated and full-length constructs with engineered glycosylation sites. Based on these results, we propose a topological model in which CarMV p9 is anchored in the membrane with its N- and C-terminal tail segments interacting with its soluble, RNA-bound partner CarMV p7, to accomplish the viral cell-to-cell movement function.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Universitat de València, E-46 100 Burjassot, Spain.
authors.forename: Marçal
authors.initials: M
authors.lastname: Vilar
authors.forename: Ana
authors.initials: A
authors.lastname: Saurí
authors.forename: Magnus
authors.initials: M
authors.lastname: Monné
authors.forename: José F
authors.initials: JF
authors.lastname: Marcos
authors.forename: Gunnar
authors.initials: G
authors.lastname: von Heijne
authors.forename: Enrique
authors.initials: E
authors.lastname: Pérez-Payá
authors.forename: Ismael
authors.initials: I
authors.lastname: Mingarro
mesh_terms: D000595:Amino Acid Sequence; D019184:Carmovirus / Q000737:chemistry*; D004721:Endoplasmic Reticulum / Q000737:chemistry*; D006031:Glycosylation; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D053830:Plant Viral Movement Proteins; D017433:Protein Structure, Secondary; D014027:Tobacco Mosaic Virus / Q000737:chemistry; D014764:Viral Proteins / Q000737:chemistry*
chemical_list: D008565:Membrane Proteins; D053830:Plant Viral Movement Proteins; D014764:Viral Proteins