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.
Highlights
Correct outer protein shell assembly is a prerequisite for virion infectivity in many multi-shelled dsRNA viruses
We determined the structure of f6 double-shelled particle by electron cryomicroscopy
The assembly of the P1 shell is initiated in vitro by P4 hexamers[26] and the C-terminus of P4 is essential for the formation of recombinant polymerase complex (PC) in vivo[41]
Summary
Correct outer protein shell assembly is a prerequisite for virion infectivity in many multi-shelled dsRNA viruses. Accumulating evidence suggests that such viruses can be grouped into a fairly small number, perhaps less than a dozen, of viral lineages, each sharing a set of common assembly principles[4,5] Explaining how such closed, highly symmetric shells may have arisen during evolution poses a challenge, as formation of a closed shell first requires a network of complementary subunit-subunit interactions with roughly 50% of the surfaces buried from solvent[6]. In RYMV, the trimers are atypical and adopt an open conformation, swapping domains with the neighbouring trimers and creating long range interactions, to which the increased stability of the capsid has been attributed[12]. It remains unclear whether RYMV trimers can exist in both open and closed conformations.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
