Cryo-EM reconstruction of the Cafeteria roenbergensis virus capsid suggests novel assembly pathway for giant viruses

• Published in: Scientific reports 2017-07, Vol.7 (1), p.5484-7, Article 5484
• Main Authors: Xiao, Chuan, Fischer, Matthias G., Bolotaulo, Duer M., Ulloa-Rondeau, Nancy, Avila, Gustavo A., Suttle, Curtis A.
• Format: Article
• Language: English
• Subjects: 101/28; 631/326/596/2148; 631/326/596/2554; 631/45/535/1258/1259; 631/535/1258/1259; Amino Acid Sequence; Capsid - ultrastructure; Capsid protein; Capsid Proteins - chemistry; Capsid Proteins - metabolism; Capsids; Cryoelectron Microscopy; Electron microscopy; Fibers; Genome, Viral; Giant Viruses - genetics; Giant Viruses - physiology; Giant Viruses - ultrastructure; Humanities and Social Sciences; Mimiviridae - genetics; Mimiviridae - physiology; Mimiviridae - ultrastructure; multidisciplinary; Protein composition; Science; Science (multidisciplinary); Virion - ultrastructure; Virus Assembly - physiology; Viruses
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-05824-w

Whereas the protein composition and overall shape of several giant virus capsids have been described, the mechanism by which these large capsids assemble remains enigmatic. Here, we present a reconstruction of the capsid of Cafeteria roenbergensis virus (CroV), one of the largest viruses analyzed by cryo-electron microscopy (cryo-EM) to date. The CroV capsid has a diameter of 3,000 Å and a Triangulation number of 499. Unlike related mimiviruses, the CroV capsid is not decorated with glycosylated surface fibers, but features 30 Å-long surface protrusions that are formed by loops of the major capsid protein. Based on the orientation of capsomers in the cryo-EM reconstruction, we propose that the capsids of CroV and related giant viruses are assembled by a newly conceived assembly pathway that initiates at a five-fold vertex and continuously proceeds outwards in a spiraling fashion.