title: Structure of a pentameric virion-associated fiber with a potential role in Orsay virus entry to host cells.
abstract: Despite the wide use of Caenorhabditis elegans as a model organism, the first virus naturally infecting this organism was not discovered until six years ago. The Orsay virus and its related nematode viruses have a positive-sense RNA genome, encoding three proteins: CP, RdRP, and a novel δ protein that shares no homology with any other proteins. δ can be expressed either as a free δ or a CP-δ fusion protein by ribosomal frameshift, but the structure and function of both δ and CP-δ remain unknown. Using a combination of electron microscopy, X-ray crystallography, computational and biophysical analyses, here we show that the Orsay δ protein forms a ~420-Å long, pentameric fiber with an N-terminal α-helical bundle, a β-stranded filament in the middle, and a C-terminal head domain. The pentameric nature of the δ fiber has been independently confirmed by both mass spectrometry and analytical ultracentrifugation. Recombinant Orsay capsid containing CP-δ shows protruding long fibers with globular heads at the distal end. Mutant viruses with disrupted CP-δ fibers were generated by organism-based reverse genetics. These viruses were found to be either non-viable or with poor infectivity according to phenotypic and qRT-PCR analyses. Furthermore, addition of purified δ proteins to worm culture greatly reduced Orsay infectivity in a sequence-specific manner. Based on the structure resemblance between the Orsay CP-δ fiber and the fibers from reovirus and adenovirus, we propose that CP-δ functions as a cell attachment protein to mediate Orsay entry into worm intestine cells.
authors.affiliation: Department of BioSciences, Rice University, MS-140, Houston, Texas, United States of America.
authors.forename: Yanlin
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Department of BioSciences, Rice University, MS-140, Houston, Texas, United States of America.
authors.forename: Yusong R
authors.initials: YR
authors.lastname: Guo
authors.affiliation: Department of BioSciences, Rice University, MS-140, Houston, Texas, United States of America.
authors.forename: Wang
authors.initials: W
authors.lastname: Yuan
authors.affiliation: Department of BioSciences, Rice University, MS-140, Houston, Texas, United States of America.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Verna & Marrs McLean Department of Biochemistry & Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, United States of America.
authors.forename: Matthew V
authors.identifier: 0000-0002-1418-6139
authors.initials: MV
authors.lastname: Holt
authors.affiliation: Verna & Marrs McLean Department of Biochemistry & Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, United States of America.
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.affiliation: The University of Texas Health Science Center at San Antonio, Department of Biochemistry, MC 7760, 7703 Floyd Curl Drive, San Antonio, Texas, United States of America.
authors.forename: Borries
authors.initials: B
authors.lastname: Demeler
authors.affiliation: Verna & Marrs McLean Department of Biochemistry & Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, United States of America.|Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, United States of America.
authors.forename: Nicolas L
authors.identifier: 0000-0002-3323-2815
authors.initials: NL
authors.lastname: Young
authors.affiliation: Department of BioSciences, Rice University, MS-140, Houston, Texas, United States of America.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Zhong
authors.affiliation: Department of BioSciences, Rice University, MS-140, Houston, Texas, United States of America.
authors.forename: Yizhi J
authors.initials: YJ
authors.lastname: Tao
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000821:virology*; D036022:Capsid Proteins / Q000737:chemistry / Q000648:ultrastructure*; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D013058:Mass Spectrometry; D046529:Microscopy, Electron, Transmission; D016297:Mutagenesis, Site-Directed; D030781:Organisms, Genetically Modified; D012327:RNA Virus Infections; D012328:RNA Viruses / Q000502:physiology* / Q000648:ultrastructure; D014771:Virion / Q000737:chemistry / Q000648:ultrastructure; D053586:Virus Internalization
chemical_list: D036022:Capsid Proteins