Structure of a pentameric virion-associated fiber with a potential role in Orsay virus entry to host cells

• Published in: PLoS pathogens 2017-02, Vol.13 (2), p.e1006231
• Main Authors: Fan, Yanlin, Guo, Yusong R, Yuan, Wang, Zhou, Ying, Holt, Matthew V, Wang, Tao, Demeler, Borries, Young, Nicolas L, Zhong, Weiwei, Tao, Yizhi J
• Format: Article
• Language: English
• Subjects: Adenoviridae; Animals; BASIC BIOLOGICAL SCIENCES; Biology and Life Sciences; Caenorhabditis elegans; Caenorhabditis elegans - virology; Capsid Proteins - chemistry; Capsid Proteins - ultrastructure; Circular Dichroism; Colleges & universities; Crystal structure; Crystallography, X-Ray; Genes; Host-virus relationships; Mass Spectrometry; Medicine and Health Sciences; Microscopy, Electron, Transmission; Mutagenesis, Site-Directed; Nematoda; Nematode infections; Nematodes; Organisms, Genetically Modified; Physical Sciences; Protein structure; Recombinant proteins; Reoviridae; Research and Analysis Methods; RNA interference; RNA Virus Infections; RNA viruses; RNA Viruses - physiology; RNA Viruses - ultrastructure; Testing; Viral packaging; Viral structure; Virion - chemistry; Virion - ultrastructure; Virulence (Microbiology); Virus Internalization; Viruses
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1006231

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.