title: Structural studies on tobacco streak virus coat protein: Insights into the pleomorphic nature of ilarviruses.
abstract: Tobacco streak virus (TSV), the type member of Ilarvirus genus, is a major plant pathogen. TSV purified from infected plants consists of a ss-RNA genome encapsidated in spheroidal particles with diameters of 27, 30 and 33nm constructed from multiple copies of a single species of coat protein (CP) subunits. Apart from protecting the viral genome, CPs of ilarviruses play several key roles in the life cycle of these viruses. Unlike the related bromo and cucumoviruses, ilarvirus particles are labile and pleomorphic, which has posed difficulties in their crystallization and structure determination. In the current study, a truncated TSV-CP was crystallized in two distinct forms and their structures were determined at resolutions of 2.4Å and 2.1Å, respectively. The core of TSV CP was found to possess the canonical β-barrel jelly roll tertiary structure observed in several other viruses. Dimers of CP with swapped C-terminal arms (C-arm) were observed in both the crystal forms. The C-arm was found to be flexible and is likely to be responsible for the polymorphic and pleomorphic nature of TSV capsids. Consistent with this observation, mutations in the hinge region of the C-arm that reduce the flexibility resulted in the formation of more uniform particles. TSV CP was found to be structurally similar to that of Alfalfa mosaic virus (AMV) accounting for similar mechanism of genome activation in alfamo and ilar viruses. This communication represents the first report on the structure of the CP from an ilarvirus.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Gulati
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Kavitha
authors.initials: K
authors.lastname: Alapati
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Abhinandan
authors.initials: A
authors.lastname: Murthy
authors.affiliation: Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India.
authors.forename: H S
authors.initials: HS
authors.lastname: Savithri
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India. Electronic address: mrn@mbu.iisc.ernet.in.
authors.forename: M R N
authors.initials: MR
authors.lastname: Murthy
mesh_terms: D017794:Alfalfa mosaic virus / Q000737:chemistry / Q000502:physiology; D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D019179:Ilarvirus / Q000737:chemistry* / Q000502:physiology; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization
chemical_list: D036022:Capsid Proteins
keywords: Capsid assembly; Coat protein; Tobacco streak virus; Viral pleomorphism; X-ray crystallography