Double-stranded RNA virus outer shell assembly by bona fide domain-swapping

• Published in: Nature communications 2017-03, Vol.8 (1), p.14814-14814, Article 14814
• Main Authors: Sun, Zhaoyang, El Omari, Kamel, Sun, Xiaoyu, Ilca, Serban L., Kotecha, Abhay, Stuart, David I., Poranen, Minna M., Huiskonen, Juha T.
• Format: Article
• Language: English
• Subjects: 101/28; 631/326/596/2148; 631/535/1258/1259; Amino Acid Sequence; Bacteriophage phi 6 - chemistry; Bacteriophage phi 6 - ultrastructure; Binding Sites; Calcium - chemistry; Calcium - metabolism; Capsid - chemistry; Capsid - ultrastructure; Capsid Proteins - chemistry; Capsid Proteins - genetics; Capsid Proteins - metabolism; Cryoelectron Microscopy; Evolution, Molecular; Gene Expression; Humanities and Social Sciences; Models, Molecular; multidisciplinary; Protein Binding; Protein Conformation, alpha-Helical; Protein Interaction Domains and Motifs; Protein Multimerization; Protein Subunits - chemistry; Protein Subunits - genetics; Protein Subunits - metabolism; Proteins; Pseudomonas syringae - virology; RNA, Double-Stranded - chemistry; RNA, Double-Stranded - genetics; RNA, Double-Stranded - metabolism; RNA, Viral - chemistry; RNA, Viral - genetics; RNA, Viral - metabolism; Rotavirus; Science; Science (multidisciplinary); Virion - chemistry; Virion - ultrastructure; Virus Assembly; Viruses
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms14814

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. Double-shelled bacteriophage φ6 is a well-studied model system used to understand assembly of dsRNA viruses. Here the authors report a near-atomic resolution cryo-EM structure of φ6 and propose a model for the structural transitions occurring in the outer shell during genome packaging.