title: The role of inter-subunit ionic interactions in the assembly of Physalis mottle tymovirus.
abstract: Physalis mottle tymovirus (PhMV) is a small spherical plant virus with its RNA genome encapsidated in a protein shell made of 180 identical coat protein (CP) subunits. The amino acid residues involved in two interfacial salt bridges, Asp-83/Arg-159 and Arg-68/Asp-150 and Lys-153, were targeted for mutagenesis with a view to delineate the role of interfacial ionic interactions in the subunit folding and assembly of the virus. R159A and D83A-R159A recombinant CP (rCP) mutants formed stable T = 3 capsids, indicating that the D83-R159 interfacial salt bridge is dispensable for the folding and assembly of PhMV. However, D150A and R68Q-D150A mutant rCPs were present in the insoluble fraction, suggesting that the R68-D150 interfacial salt bridge is crucial for subunit folding and assembly. Similarly, K153Q, D83A-K153Q, and H69A-K153Q mutant rCPs were present in the insoluble fraction. Interestingly, the R68Q-D150A, D83A-K153Q, and H69A-K153Q double mutant rCPs could be refolded into partially folded soluble heterogeneous aggregates of 14-16 S. The results further confirm our earlier observation that subunit folding and assembly are concerted events in PhMV.
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore, India.
authors.forename: M
authors.initials: M
authors.lastname: Umashankar
authors.forename: M R N
authors.initials: MR
authors.lastname: Murthy
authors.forename: S A
authors.initials: SA
authors.lastname: Singh
authors.forename: A G
authors.initials: AG
authors.lastname: Appu Rao
authors.forename: H S
authors.initials: HS
authors.lastname: Savithri
mesh_terms: D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007477:Ions / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D032321:Physalis / Q000821:virology*; D017510:Protein Folding; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017806:Tymovirus / Q000737:chemistry / Q000502:physiology*; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D007477:Ions; D021122:Protein Subunits; D011994:Recombinant Proteins