title: Backbone trace of partitivirus capsid protein from electron cryomicroscopy and homology modeling.
abstract: Most dsRNA viruses have a genome-enclosing capsid that comprises 120 copies of a single coat protein (CP). These 120 CP subunits are arranged as asymmetrical dimers that surround the icosahedral fivefold axes, forming pentamers of dimers that are thought to be assembly intermediates. This scheme is violated, however, in recent structures of two dsRNA viruses, a fungal virus from family Partitiviridae and a rabbit virus from family Picobirnaviridae, both of which have 120 CP subunits organized as dimers of quasisymmetrical dimers. In this study, we report the CP backbone trace of a second fungal partitivirus, determined in this case by electron cryomicroscopy and homology modeling. This virus also exhibits quasisymmetrical CP dimers that are connected by prominent surface arches and stabilized by domain swapping between the two CP subunits. The CP fold is dominated by alpha-helices, although beta-strands mediate several important contacts. A dimer-of-dimers assembly intermediate is again implicated. The disordered N-terminal tail of each CP subunit protrudes into the particle interior and likely interacts with the genome during packaging and/or transcription. These results broaden our understanding of conserved and variable aspects of partitivirus structure and reflect the growing use of electron cryomicroscopy for atomic modeling of protein folds.
authors.affiliation: Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, California 92037, USA.
authors.forename: Jinghua
authors.initials: J
authors.lastname: Tang
authors.forename: Junhua
authors.initials: J
authors.lastname: Pan
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Havens
authors.forename: Wendy F
authors.initials: WF
authors.lastname: Ochoa
authors.forename: Tom S Y
authors.initials: TS
authors.lastname: Guu
authors.forename: Said A
authors.initials: SA
authors.lastname: Ghabrial
authors.forename: Max L
authors.initials: ML
authors.lastname: Nibert
authors.forename: Yizhi Jane
authors.initials: YJ
authors.lastname: Tao
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Baker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D036022:Capsid Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D016679:Genome, Viral / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010316:Particle Size; D018708:Picobirnavirus / Q000235:genetics; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D012328:RNA Viruses / Q000235:genetics / Q000648:ultrastructure*; D011817:Rabbits; D040681:Structural Homology, Protein; D014158:Transcription, Genetic
chemical_list: D036022:Capsid Proteins