title: BAP31 and BiP are essential for dislocation of SV40 from the endoplasmic reticulum to the cytosol.
abstract: How non-enveloped viruses overcome host cell membranes is poorly understood. Here, we show that after endocytosis and transport to the endoplasmic reticulum (ER), but before crossing the ER membrane to the cytosol, incoming simian virus 40 particles are structurally remodelled leading to exposure of the amino-terminal sequence of the minor viral protein VP2. These hydrophobic sequences anchor the virus to membranes. A negatively charged residue, Glu 17, in the α-helical, membrane-embedded peptide is essential for infection, most likely by introducing an 'irregularity' recognized by the ER-associated degradation (ERAD) system for membrane proteins. Using a siRNA-mediated screen, the lumenal chaperone BiP and the ER-membrane protein BAP31 (both involved in ERAD) were identified as being essential for infection. They co-localized with the virus in discrete foci and promoted its ER-to-cytosol dislocation. Virus-like particles devoid of VP2 failed to cross the membrane. The results demonstrated that ERAD-factors assist virus transport across the ER membrane.
authors.affiliation: Institute of Biochemistry, ETH Zurich, Schafmattstrasse 18, CH-8093 Zurich, Switzerland.
authors.forename: Roger
authors.initials: R
authors.lastname: Geiger
authors.forename: Daniel
authors.initials: D
authors.lastname: Andritschke
authors.forename: Sarah
authors.initials: S
authors.lastname: Friebe
authors.forename: Fabian
authors.initials: F
authors.lastname: Herzog
authors.forename: Stefania
authors.initials: S
authors.lastname: Luisoni
authors.forename: Thomas
authors.initials: T
authors.lastname: Heger
authors.forename: Ari
authors.initials: A
authors.lastname: Helenius
mesh_terms: D036022:Capsid Proteins / Q000737:chemistry / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism* / Q000821:virology; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000821:virology; D000091342:Endoplasmic Reticulum Chaperone BiP; D060746:Endoplasmic Reticulum-Associated Degradation; D018698:Glutamic Acid; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007425:Intracellular Membranes / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013539:Simian virus 40 / Q000378:metabolism* / Q000472:pathogenicity; D014162:Transfection; D014771:Virion; D053585:Virus Attachment
chemical_list: C091247:BCAP31 protein, human; D036022:Capsid Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D008081:Liposomes; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C062481:VP1 protein, polyomavirus; C514199:Vp2 protein, simian virus 40; D018698:Glutamic Acid