Name
Structural and functional analysis of infectious bursal disease virus VP4 helical assemblies
Presenter
Juan Manuel Martínez Romero, National Center for Biotechnology (CNB-CSIC)
Co-Author(s)
Juan M. Martínez-Romero1, Mariana Castrillo1, José M. Fernandez-Palacios1, Guy Novoa1, Esther Martín-Forero1, Javier M. Rodríguez1, Daniel Luque2, José R. Castón1*
1Department of Macromolecular Structures, Centro Nacional de Biotecnología (CNB-CSIC), Madrid, Spain.
2School of Biomedical Sciences, Faculty of Medicine & Health, University of New South Wales, Sydney, Australia
Abstract Category
Structural Biology
Abstract
IBDV is an icosahedral virus from the Birnaviridae family, whose two dsRNA segments (A and B) are organized as ribonucleoprotein complexes. An ORF of segment A encodes a polyprotein, NH2-pVP2-VP4-VP3-COOH, which is self-cleaved by the protease VP4 (243 residues) rendering pVP2 and VP3. Segment B encodes the RNA polymerase VP1. VP1-VP4 and the genomic dsRNA associate into three assemblies crucial during the viral life cycle: T=13 capsids, VP4 helical tubes, and the RNPs.
VP4 is naturally found as helical assemblies, ~25 nm in diameter, in IBDV-infected cells. VP4 atomic structures are conserved in birnaviruses, but no structural data are available for these in vivo assemblies. We determined the cryo-EM structure of VP4 helix at 2.4 Å resolution. The basic building blocks are VP4 dimers, arranged in a right-handed three-stranded helix, with an axial rise of 18.4 Å and an azimuth angle of 40.6º. The catalytic Ser/Lys dyad, located in a surface crevice, is blocked in cis by the VP4 C-terminal end, which is also involved in intra-dimeric interactions via the 227-243 C-terminal segment. Interdimeric interactions occur via segments 209-218 and 150-155 within the same helix, and via segment 89-112 between dimers of different helices. A collection of mutants has confirmed key residues for VP4 activity, self-assembly, and infection viability. Our study suggests that once VP4 has completed proteolysis, it is securely inactivated by assembly into helical structures to prevent lethal damage to the virus or to the host components needed for virus multiplication, and offers insights into new antiviral targets.
VP4 is naturally found as helical assemblies, ~25 nm in diameter, in IBDV-infected cells. VP4 atomic structures are conserved in birnaviruses, but no structural data are available for these in vivo assemblies. We determined the cryo-EM structure of VP4 helix at 2.4 Å resolution. The basic building blocks are VP4 dimers, arranged in a right-handed three-stranded helix, with an axial rise of 18.4 Å and an azimuth angle of 40.6º. The catalytic Ser/Lys dyad, located in a surface crevice, is blocked in cis by the VP4 C-terminal end, which is also involved in intra-dimeric interactions via the 227-243 C-terminal segment. Interdimeric interactions occur via segments 209-218 and 150-155 within the same helix, and via segment 89-112 between dimers of different helices. A collection of mutants has confirmed key residues for VP4 activity, self-assembly, and infection viability. Our study suggests that once VP4 has completed proteolysis, it is securely inactivated by assembly into helical structures to prevent lethal damage to the virus or to the host components needed for virus multiplication, and offers insights into new antiviral targets.