Molecular substructure of a viral receptor-recognition protein. The gp17 tail-fiber of bacteriophage T7

J Mol Biol. 1988 Mar 20;200(2):351-65. doi: 10.1016/0022-2836(88)90246-x.


The bacteriophage T7 tail complex consists of a conical tail-tube surrounded by six kinked tail-fibers, which are oligomers of the viral protein gp17 (Mr 61,400). We have derived a molecular model for the tail-fiber by integrating secondary structure predictions with ultrastructural information obtained by correlation averaging of electron micrographs of negatively stained tail complexes. This model has been further refined by high-resolution scanning transmission electron microscopy of purified fibers, both negatively stained and unstained. Mass measurements made from the latter images establish that the fiber is a trimer of gp17. The proximal half-fiber is a uniform rod, about 2.0 nm in diameter and 16.4 nm long, which we infer to be a triple-stranded coiled-coil, containing three copies of an alpha-helical domain of about 117 residues, starting at Phe151. The distal half-fiber is 15.5 nm long, and is made up of four globules, 3.1 to 4.8 nm in diameter, in rigid linear array: it contains the carboxy-terminal halves (residues approximately 268 to 553) of the constituent gp17 chains, arranged with 3-fold symmetry around its long axis. The amino-terminal domains (residues 1 to 149) link the fiber to the tail-tube. We conclude that the three gp17 chains are quasi-equivalent in the proximal half-fiber, equivalent in the distal half-fiber, and non-equivalent in the kink region that separates the two half-fibers: such localized non-equivalence may represent a general mechanism for the formation of kinked joints in segmented homo-oligomeric proteins.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Hot Temperature
  • Macromolecular Substances
  • Microscopy, Electron, Scanning
  • Protein Conformation
  • Receptors, Virus
  • T-Phages / analysis*
  • Viral Proteins* / isolation & purification


  • Macromolecular Substances
  • Receptors, Virus
  • Viral Proteins