title: Double-stranded RNA virus outer shell assembly by bona fide domain-swapping.
abstract: Correct outer protein shell assembly is a prerequisite for virion infectivity in many multi-shelled dsRNA viruses. In the prototypic dsRNA bacteriophage φ6, the assembly reaction is promoted by calcium ions but its biomechanics remain poorly understood. Here, we describe the near-atomic resolution structure of the φ6 double-shelled particle. The outer T=13 shell protein P8 consists of two alpha-helical domains joined by a linker, which allows the trimer to adopt either a closed or an open conformation. The trimers in an open conformation swap domains with each other. Our observations allow us to propose a mechanistic model for calcium concentration regulated outer shell assembly. Furthermore, the structure provides a prime exemplar of bona fide domain-swapping. This leads us to extend the theory of domain-swapping from the level of monomeric subunits and multimers to closed spherical shells, and to hypothesize a mechanism by which closed protein shells may arise in evolution.
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Sun
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.
authors.forename: Kamel
authors.identifier: 0000-0003-3506-6045
authors.initials: K
authors.lastname: El Omari
authors.affiliation: Department of Biosciences, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland.
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Sun
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.
authors.forename: Serban L
authors.initials: SL
authors.lastname: Ilca
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.
authors.forename: Abhay
authors.identifier: 0000-0002-4480-5439
authors.initials: A
authors.lastname: Kotecha
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.
authors.forename: David I
authors.initials: DI
authors.lastname: Stuart
authors.affiliation: Department of Biosciences, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland.
authors.forename: Minna M
authors.initials: MM
authors.lastname: Poranen
authors.affiliation: Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.|Department of Biosciences, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland.
authors.forename: Juha T
authors.identifier: 0000-0002-0348-7323
authors.initials: JT
authors.lastname: Huiskonen
mesh_terms: D000595:Amino Acid Sequence; D017126:Bacteriophage phi 6 / Q000737:chemistry / Q000648:ultrastructure*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002213:Capsid / Q000737:chemistry / Q000648:ultrastructure; D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020285:Cryoelectron Microscopy; D019143:Evolution, Molecular; D015870:Gene Expression; D008958:Models, Molecular; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D044224:Pseudomonas syringae / Q000821:virology; D012330:RNA, Double-Stranded / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014771:Virion / Q000737:chemistry / Q000648:ultrastructure*; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D021122:Protein Subunits; D012330:RNA, Double-Stranded; D012367:RNA, Viral; D002118:Calcium