Atomic structure of bacteriophage Sf6 tail needle knob

J Biol Chem. 2011 Sep 2;286(35):30867-30877. doi: 10.1074/jbc.M111.260877. Epub 2011 Jun 25.


Podoviridae are double-stranded DNA bacteriophages that use short, non-contractile tails to adsorb to the host cell surface. Within the tail apparatus of P22-like phages, a dedicated fiber known as the "tail needle" likely functions as a cell envelope-penetrating device to promote ejection of viral DNA inside the host. In Sf6, a P22-like phage that infects Shigella flexneri, the tail needle presents a C-terminal globular knob. This knob, absent in phage P22 but shared in other members of the P22-like genus, represents the outermost exposed tip of the virion that contacts the host cell surface. Here, we report a crystal structure of the Sf6 tail needle knob determined at 1.0 Å resolution. The structure reveals a trimeric globular domain of the TNF fold structurally superimposable with that of the tail-less phage PRD1 spike protein P5 and the adenovirus knob, domains that in both viruses function in receptor binding. However, P22-like phages are not known to utilize a protein receptor and are thought to directly penetrate the host surface. At 1.0 Å resolution, we identified three equivalents of l-glutamic acid (l-Glu) bound to each subunit interface. Although intimately bound to the protein, l-Glu does not increase the structural stability of the trimer nor it affects its ability to self-trimerize in vitro. In analogy to P22 gp26, we suggest the tail needle of phage Sf6 is ejected through the bacterial cell envelope during infection and its C-terminal knob is threaded through peptidoglycan pores formed by glycan strands.

Publication types

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

MeSH terms

  • Adenoviridae / metabolism
  • Bacteriophages / chemistry*
  • Bacteriophages / metabolism
  • Bacteriophages / ultrastructure
  • Cell Cycle
  • Chromatin / chemistry
  • Crystallography, X-Ray / methods
  • DNA, Viral / metabolism
  • Microscopy, Electron, Transmission / methods
  • Models, Biological
  • Models, Molecular
  • Molecular Conformation
  • Oligonucleotide Array Sequence Analysis
  • Protein Structure, Tertiary
  • Shigella flexneri / metabolism*
  • Shigella flexneri / virology
  • Transcription, Genetic
  • Viral Tail Proteins / chemistry*


  • Chromatin
  • DNA, Viral
  • Viral Tail Proteins

Associated data

  • PDB/3RWN