Structural investigations of a Podoviridae streptococcus phage C1, implications for the mechanism of viral entry

Proc Natl Acad Sci U S A. 2012 Aug 28;109(35):14001-6. doi: 10.1073/pnas.1207730109. Epub 2012 Aug 13.


The Podoviridae phage C1 was one of the earliest isolated bacteriophages and the first virus documented to be active against streptococci. The icosahedral and asymmetric reconstructions of the virus were calculated using cryo-electron microscopy. The capsid protein has an HK97 fold arranged into a T = 4 icosahedral lattice. The C1 tail is terminated with a ϕ29-like knob, surrounded by a skirt of twelve long appendages with novel morphology. Several C1 structural proteins have been identified, including a candidate for an appendage. The crystal structure of the knob has an N-terminal domain with a fold observed previously in tube forming proteins of Siphoviridae and Myoviridae phages. The structure of C1 suggests the mechanisms by which the virus digests the cell wall and ejects its genome. Although there is little sequence similarity to other phages, conservation of the structural proteins demonstrates a common origin of the head and tail, but more recent evolution of the appendages.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Capsid / chemistry
  • Capsid / ultrastructure
  • Capsid Proteins / chemistry*
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Myoviridae / growth & development
  • Myoviridae / ultrastructure
  • Podoviridae / growth & development*
  • Podoviridae / ultrastructure
  • Protein Structure, Tertiary
  • Streptococcus / virology*
  • Streptococcus Phages / growth & development*
  • Streptococcus Phages / ultrastructure
  • Viral Structural Proteins / chemistry*
  • Virus Replication / physiology


  • Capsid Proteins
  • Viral Structural Proteins

Associated data

  • PDB/4EO2
  • PDB/4EP0