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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.

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,
TITLE="Molecular Substructure of a Viral Receptor-Recognition
        Protein. The {gp17} Tail-Fiber of Bacteriophage {T7}",
JOURNAL="Journal of Molecular Biology",

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