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PLoS Pathog. 2017 Dec 8;13(12):e1006755. doi: 10.1371/journal.ppat.1006755. eCollection 2017 Dec.

Acquisition of functions on the outer capsid surface during evolution of double-stranded RNA fungal viruses.

Author information

1
Department of Structure of Macromolecules, Centro Nacional de Biotecnología (CNB-CSIC), Campus Cantoblanco, Madrid, Spain.
2
Centro Nacional de Microbiología/ISCIII, Majadahonda, Madrid, Spain.
3
Institute of Plant Science and Resources, Okayama, Japan.
4
Department of Plant Pathology, University of Kentucky, Lexington, KY, United States of America.
5
Imaging Sciences Laboratory, CIT, NIH, Bethesda, MD, United States of America.

Abstract

Unlike their counterparts in bacterial and higher eukaryotic hosts, most fungal viruses are transmitted intracellularly and lack an extracellular phase. Here we determined the cryo-EM structure at 3.7 Å resolution of Rosellinia necatrix quadrivirus 1 (RnQV1), a fungal double-stranded (ds)RNA virus. RnQV1, the type species of the family Quadriviridae, has a multipartite genome consisting of four monocistronic segments. Whereas most dsRNA virus capsids are based on dimers of a single protein, the ~450-Å-diameter, T = 1 RnQV1 capsid is built of P2 and P4 protein heterodimers, each with more than 1000 residues. Despite a lack of sequence similarity between the two proteins, they have a similar α-helical domain, the structural signature shared with the lineage of the dsRNA bluetongue virus-like viruses. Domain insertions in P2 and P4 preferential sites provide additional functions at the capsid outer surface, probably related to enzyme activity. The P2 insertion has a fold similar to that of gelsolin and profilin, two actin-binding proteins with a function in cytoskeleton metabolism, whereas the P4 insertion suggests protease activity involved in cleavage of the P2 383-residue C-terminal region, absent in the mature viral particle. Our results indicate that the intimate virus-fungus partnership has altered the capsid genome-protective and/or receptor-binding functions. Fungal virus evolution has tended to allocate enzyme activities to the virus capsid outer surface.

PMID:
29220409
PMCID:
PMC5738138
DOI:
10.1371/journal.ppat.1006755
[Indexed for MEDLINE]
Free PMC Article

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