title: Electrostatic interactions between capsid and scaffolding proteins mediate the structural polymorphism of a double-stranded RNA virus.
abstract: Capsid proteins that adopt distinct conformations constitute a paradigm of the structural polymorphism of macromolecular assemblies. We show the molecular basis of the flexibility mechanism of VP2, the capsid protein of the double-stranded RNA virus infectious bursal disease virus. The initial assembly, a procapsid-like structure, is built by the protein precursor pVP2 and requires VP3, the other infectious bursal disease virus major structural protein, which acts as a scaffold. The pVP2 C-terminal region, which is proteolyzed during virus maturation, contains an amphipathic alpha-helix that acts as a molecular switch. In the absence of VP3, efficient virus-like particle assembly occurs when the structural unit is a VP2-based chimeric protein with an N-terminal-fused His(6) tag. The His tag has a positively charged N terminus and a negatively charged C terminus, both important for virion-like structure assembly. The charge distributions of the VP3 C terminus and His tag are similar. We tested whether the His tag emulates the role of VP3 and found that the presence of a VP3 C-terminal peptide in VP2-based chimeric proteins resulted in the assembly of virus-like particles. We analyzed the electrostatic interactions between these two charged morphogenetic peptides, in which a single residue was mutated to impede the predicted interaction, followed by a compensatory double mutation to rescue electrostatic interactions. The effects of these mutations were monitored by following the virus-like and/or virus-related assemblies. Our results suggest that the basic face of the pVP2 amphipathic alpha-helix interacts with the acidic region of the VP3 C terminus and that this interaction is essential for VP2 acquisition of competent conformations for capsid assembly.
authors.affiliation: From the Departments of Structure of Macromolecules, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Saugar
authors.affiliation: Molecular and Cellular Biology, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain.
authors.forename: Nerea
authors.initials: N
authors.lastname: Irigoyen
authors.affiliation: From the Departments of Structure of Macromolecules, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Luque
authors.affiliation: From the Departments of Structure of Macromolecules, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Carrascosa
authors.affiliation: Molecular and Cellular Biology, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain.
authors.forename: José F
authors.initials: JF
authors.lastname: Rodríguez
authors.affiliation: From the Departments of Structure of Macromolecules, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Científicas, Cantoblanco, 28049 Madrid, Spain. Electronic address: jrcaston@cnb.csic.es.
authors.forename: José R
authors.initials: JR
authors.lastname: Castón
mesh_terms: D015153:Blotting, Western; D002213:Capsid / Q000378:metabolism; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007243:Infectious bursal disease virus / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009154:Mutation; D012328:RNA Viruses / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D055672:Static Electricity; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014771:Virion / Q000378:metabolism; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D014764:Viral Proteins