title: Maturation in action: CryoEM study of a viral capsid caught during expansion.
abstract: Bacteriophage HK97 maturation involves discrete intermediate particle forms, comparable to transitional states in protein folding, before reaching its mature form. The process starts by formation of a metastable prohead, poised for exothermic expansion triggered by DNA packaging. During maturation, the capsid subunit transitions from a strained to a canonical tertiary conformation and this has been postulated to be the driving mechanism for initiating expansion via switching hexameric capsomer architecture from skewed to 6-fold symmetric. We report the subnanometer electron-cryomicroscopy reconstruction of the HK97 first expansion intermediate before any crosslink formation. This form displays 6-fold symmetric hexamers, but capsid subunit tertiary structures exhibit distortions comparable to the prohead forms. We propose that coat subunit strain release acts in synergy with the first crosslinks to drive forward maturation. Finally, we speculate that the energetic features of this transition may result from increased stability of intermediates during maturation via enhanced inter-subunit interactions.
authors: Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors: David
authors: D
authors: Veesler
authors: Joel
authors: J
authors: Quispe
authors: Nikolaus
authors: N
authors: Grigorieff
authors: Clinton S
authors: CS
authors: Potter
authors: Bridget
authors: B
authors: Carragher
authors: John E
authors: JE
authors: Johnson
mesh_terms: D019943:Amino Acid Substitution; D001435:Bacteriophages / Q000737:chemistry* / Q000502:physiology; D002213:Capsid / Q000737:chemistry*; D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics; D020285:Cryoelectron Microscopy; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D021122:Protein Subunits