Structural polymorphism of the major capsid protein of a double-stranded RNA virus: an amphipathic alpha helix as a molecular switch.
The infectious bursal disease virus T=13 viral particle is composed of two major proteins, VP2 and VP3. Here, we show that the molecular basis of the conformational flexibility of the major capsid protein precursor, pVP2, is an amphipatic alpha helix formed by the sequence GFKDIIRAIR. VP2 containing this alpha helix is able to assemble into the T=13 capsid only when expressed as a chimeric protein with an N-terminal His tag. An amphiphilic alpha helix, which acts as a conformational switch, is thus responsible for the inherent structural polymorphism of VP2. The His tag mimics the VP3 C-terminal region closely and acts as a molecular triggering factor. Using cryo-electron microscopy difference imaging, both polypeptide elements were detected on the capsid inner surface. We propose that electrostatic interactions between these two morphogenic elements are transmitted to VP2 to acquire the competent conformations for capsid assembly.
Saugar
Irene
I
Department of Structure of Macromolecules, Centro Nacional de Biotecnología/CSIC, Campus Universidad Autónoma de Madrid, 28049 Madrid, Spain.
Luque
Daniel
D
Oña
Ana
A
Rodríguez
José F
JF
Carrascosa
José L
JL
Trus
Benes L
BL
Castón
José R
JR
D000595:Amino Acid Sequence; D016367:Baculoviridae / Q000235:genetics; D015153:Blotting, Western; D002213:Capsid / Q000737:chemistry*; D036022:Capsid Proteins / Q000737:chemistry; D002942:Circular Dichroism; D020285:Cryoelectron Microscopy; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000737:chemistry; D007091:Image Processing, Computer-Assisted; D007243:Infectious bursal disease virus / Q000235:genetics*; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D011110:Polymorphism, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012328:RNA Viruses / Q000235:genetics*; D055672:Static Electricity
D036022:Capsid Proteins; D010455:Peptides; D049452:Green Fluorescent Proteins