Structure of Nora virus at 2.7 Å resolution and implications for receptor binding, capsid stability and taxonomy

Pasi Laurinmäki, Shabih Shakeel, Jens Ola Ekström, Pezhman Mohammadi, Dan Hultmark, Sarah J. Butcher (Corresponding Author)

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Nora virus, a virus of Drosophila, encapsidates one of the largest single-stranded RNA virus genomes known. Its taxonomic affinity is uncertain as it has a picornavirus-like cassette of enzymes for virus replication, but the capsid structure was at the time for genome publication unknown. By solving the structure of the virus, and through sequence comparison, we clear up this taxonomic ambiguity in the invertebrate RNA virosphere. Despite the lack of detectable similarity in the amino acid sequences, the 2.7 Å resolution cryoEM map showed Nora virus to have T = 1 symmetry with the characteristic capsid protein β-barrels found in all the viruses in the Picornavirales order. Strikingly, α-helical bundles formed from the extended C-termini of capsid protein VP4B and VP4C protrude from the capsid surface. They are similar to signalling molecule folds and implicated in virus entry. Unlike other viruses of Picornavirales, no intra-pentamer stabilizing annulus was seen, instead the intra-pentamer stability comes from the interaction of VP4C and VP4B N-termini. Finally, intertwining of the N-termini of two-fold symmetry-related VP4A capsid proteins and RNA, provides inter-pentamer stability. Based on its distinct structural elements and the genetic distance to other picorna-like viruses we propose that Nora virus, and a small group of related viruses, should have its own family within the order Picornavirales.
Original languageEnglish
Article number19675
JournalScientific Reports
Issue number1
Publication statusPublished - 12 Nov 2020
MoE publication typeA1 Journal article-refereed


We acknowledge the Diamond Light Source for access to the cryoEM facilities at the UK national electron bio-imaging centre (eBIC), proposal EM14263-1, funded by the Wellcome Trust, MRC and BBSRC. The CSC-IT Center for Science Ltd., Biocenter Finland, Instruct-ERIC Centre Finland and Instruct-FI cryoEM unit provided facilities. This study was supported by the Academy of Finland (275199, 315950, 328112 to SJB, 252384 to DH), the Sigrid Juselius Foundation (SJB, DH) and the Swedish Research Council (DH).


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