Structure of a Bacterial Virus DNA-Injection Protein Complex Reveals a Decameric Assembly with a Constricted Molecular Channel

PLoS One. 2016 Feb 16;11(2):e0149337. doi: 10.1371/journal.pone.0149337. eCollection 2016.


The multi-layered cell envelope structure of Gram-negative bacteria represents significant physical and chemical barriers for short-tailed phages to inject phage DNA into the host cytoplasm. Here we show that a DNA-injection protein of bacteriophage Sf6, gp12, forms a 465-kDa, decameric assembly in vitro. The electron microscopic structure of the gp12 assembly shows a ~150-Å, mushroom-like architecture consisting of a crown domain and a tube-like domain, which embraces a 25-Å-wide channel that could precisely accommodate dsDNA. The constricted channel suggests that gp12 mediates rapid, uni-directional injection of phage DNA into host cells by providing a molecular conduit for DNA translocation. The assembly exhibits a 10-fold symmetry, which may be a common feature among DNA-injection proteins of P22-like phages and may suggest a symmetry mismatch with respect to the 6-fold symmetric phage tail. The gp12 monomer is highly flexible in solution, supporting a mechanism for translocation of the protein through the conduit of the phage tail toward the host cell envelope, where it assembles into a DNA-injection device.

Publication types

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

MeSH terms

  • Bacteriophages / genetics*
  • DNA, Viral / chemistry*
  • Imaging, Three-Dimensional
  • Models, Molecular*
  • Protein Multimerization*
  • Protein Structure, Tertiary
  • Solutions
  • Viral Proteins / chemistry*
  • Viral Proteins / metabolism


  • DNA, Viral
  • Solutions
  • Viral Proteins