Molecular Substructure of a Viral Receptor-Recognition Protein. The gp17 Tail-Fiber of Bacteriophage T7
A.C. Steven, B.L. Trus, J.V. Maizel, M. Unser, D.A. Parry, J.S. Wall, J.F. Hainfeld, F.W. Studier
Journal of Molecular Biology, vol. 200, no. 2, pp. 351–365, March 1988.
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.
@ARTICLE(http://bigwww.epfl.ch/publications/steven8801.html,
AUTHOR="Steven, A.C. and Trus, B.L. and Maizel, J.V. and Unser, M.
and Parry, D.A. and Wall, J.S. and Hainfeld, J.F. and Studier,
F.W.",
TITLE="Molecular Substructure of a Viral Receptor-Recognition
Protein. The {gp17} Tail-Fiber of Bacteriophage {T7}",
JOURNAL="Journal of Molecular Biology",
YEAR="1988",
volume="200",
number="2",
pages="351--365",
month="March",
note="")