Bacteriophage P22 capsid size determination: roles for the coat protein telokin-like domain and the scaffolding protein amino-terminus

Virology. 2011 Sep 1;417(2):418-29. doi: 10.1016/j.virol.2011.06.025. Epub 2011 Jul 23.


Assembly of icosahedral capsids of proper size and symmetry is not understood. Residue F170 in bacteriophage P22 coat protein is critical for conformational switching during assembly. Substitutions at this site cause assembly of tubes of hexamerically arranged coat protein. Intragenic suppressors of the ts phenotype of F170A and F170K coat protein mutants were isolated. Suppressors were repeatedly found in the coat protein telokin-like domain at position 285, which caused coat protein to assemble into petite procapsids and capsids. Petite capsid assembly strongly correlated to the side chain volume of the substituted amino acid. We hypothesize that larger side chains at position 285 torque the telokin-like domain, changing flexibility of the subunit and intercapsomer contacts. Thus, a single amino acid substitution in coat protein is sufficient to change capsid size. In addition, the products of assembly of the variant coat proteins were affected by the size of the internal scaffolding protein.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Substitution / genetics
  • Bacteriophage P22 / metabolism
  • Bacteriophage P22 / physiology*
  • Bacteriophage P22 / ultrastructure
  • Capsid / metabolism
  • Capsid / physiology*
  • Capsid / ultrastructure
  • Capsid Proteins / genetics
  • Capsid Proteins / metabolism*
  • Microscopy, Electron
  • Models, Molecular
  • Mutation, Missense
  • Myosin-Light-Chain Kinase / genetics
  • Peptide Fragments / genetics
  • Protein Structure, Tertiary
  • Suppression, Genetic
  • Viral Structural Proteins / metabolism*
  • Virus Assembly*


  • Capsid Proteins
  • Peptide Fragments
  • Viral Structural Proteins
  • scaffolding protein, bacteriophage P22
  • telokin
  • Myosin-Light-Chain Kinase