title: Maturation of a tetravirus capsid alters the dynamic properties and creates a metastable complex.
abstract: The assembly of monomeric protein subunits into a viral capsid is a finely tuned molecular process. In response to subtle changes in environmental conditions, this supramolecular complex can dramatically reorganize. Defining the forces that control this structure and the cooperative action of subunits has implications for biology and nanotechnology. The small icosahedral RNA tetravirus family members Nudaurelia omega capensis (NomegaV) and Helicoverpa armigera stunt virus (HaSV) can be purified as provirions, and maturation to capsids can be induced by a drop in pH. In this study, a comparison of capsid secondary structure using FT-IR revealed that the procapsid has more alpha-helical content than the capsid, supporting the proposal that helix to coil transition may be important for maturation. The dynamic properties of the two states were probed using limited proteolysis and peptide mass mapping to identify regions of significant flexibility. Interestingly, the initial sites of protease cleavage were the N and C terminal domains that are internal in high-resolution models, and to inter-subunit surfaces. Further comparison of the two particle forms using FT-IR revealed that in response to thermal stress, the provirion disassembles and unfolds in a cooperative manner over a narrow temperature range (approximately 5 degrees C). Paradoxically, the capsid form, which is stable in a wide range of pH and ionic conditions and is more resistant to proteolysis, responds to thermal stress at a lower temperature than the procapsid form. This suggests that a metastable state is the end product of assembly.
authors.affiliation: Scripps Research Institute, Department of Molecular Biology, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA. bbothner@chemistry.montana.edu
authors.forename: Brian
authors.initials: B
authors.lastname: Bothner
authors.forename: Derek
authors.initials: D
authors.lastname: Taylor
authors.forename: Bokkyoo
authors.initials: B
authors.lastname: Jun
authors.forename: Kelly K
authors.initials: KK
authors.lastname: Lee
authors.forename: Gary
authors.initials: G
authors.lastname: Siuzdak
authors.forename: Christian P
authors.initials: CP
authors.lastname: Schultz
authors.forename: Christian P
authors.initials: CP
authors.lastname: Schlutz
authors.forename: John E
authors.initials: JE
authors.lastname: Johnson
mesh_terms: D000818:Animals; D002213:Capsid / Q000737:chemistry / Q000502:physiology*; D036022:Capsid Proteins / Q000737:chemistry / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007915:Lepidoptera / Q000821:virology; D046911:Macromolecular Substances; D008958:Models, Molecular; D009994:Osmolar Concentration; D010447:Peptide Hydrolases; D010449:Peptide Mapping; D017433:Protein Structure, Secondary; D012328:RNA Viruses / Q000737:chemistry / Q000502:physiology*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D046911:Macromolecular Substances; D010447:Peptide Hydrolases