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The hallmark of a virus is its capsid, which harbors the viral genome and is formed from protein subunits, which assemble following precise geometric rules. dsRNA viruses use an unusual protein multiplicity (120 copies) to form their closed capsids. We have determined the atomic structure of the capsid protein (P1) from the dsRNA cystovirus Φ8. In the crystal P1 forms pentamers, very similar in shape to facets of empty procapsids, suggesting an unexpected assembly pathway that proceeds via a pentameric intermediate. Unlike the elongated proteins used by dsRNA mammalian reoviruses, P1 has a compact trapezoid-like shape and a distinct arrangement in the shell, with two near-identical conformers in nonequivalent structural environments. Nevertheless, structural similarity with the analogous protein from the mammalian viruses suggests a common ancestor. The unusual shape of the molecule may facilitate dramatic capsid expansion during phage maturation, allowing P1 to switch interaction interfaces to provide capsid plasticity.

Original publication

DOI

10.1016/j.str.2013.06.017

Type

Journal article

Journal

Structure

Publication Date

06/08/2013

Volume

21

Pages

1384 - 1395

Keywords

Capsid, Capsid Proteins, Crystallography, X-Ray, Cystoviridae, Models, Molecular, Protein Interaction Domains and Motifs, Protein Structure, Quaternary, Protein Structure, Secondary, Pseudomonas Phages, Reoviridae, Structural Homology, Protein, Virus Assembly