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Journal of Bacteriology, February 2005, p. 1055-1066, Vol. 187, No. 3
0021-9193/05/$08.00+0     doi:10.1128/JB.187.3.1055-1066.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

gpwac of the T4-Type Bacteriophages: Structure, Function, and Evolution of a Segmented Coiled-Coil Protein That Controls Viral Infectivity

A. Letarov,^1, X. Manival,^1, C. Desplats,^1, and H. M. Krisch^1*

Laboratoire de Microbiologie et Génétique Moléculaire du CNRS, UMR 5100, Toulouse, France¹

Received 7 July 2004/ Accepted 18 October 2004

The wac gene product (gpwac) or fibritin of bacteriophage T4 forms the six fibers that radiate from the phage neck. During phage morphogenesis these whiskers bind the long tail fibers (LTFs) and facilitate their attachment to the phage baseplate. After the cell lysis, the gpwac fibers function as part of an environmental sensing device that retains the LTFs in a retracted configuration and thus prevents phage adsorption in unfavorable conditions. A comparative analysis of the sequences of 5 wac gene orthologs from various T4-type phages reveals that the 50-amino-acid N-terminal domain is the only highly conserved segment of the protein. This sequence conservation is probably a direct consequence of the domain's strong and specific interactions with the neck proteins. The sequence of the central fibrous region of gpwac is highly plastic, with only the heptad periodicity of the coiled-coil structure being conserved. In the various gpwac sequences, the small C-terminal domain essential for initiation of the folding of T4 gpwac is replaced by unrelated sequences of unknown origin. When a distant T4-type phage has a novel C-terminal gpwac sequence, the phage's gp36 sequence that is located at the knee joint of the LTF invariably has a novel domain in its C terminus as well. The covariance of these two sequences is compatible with genetic data suggesting that the C termini of gpwac and gp36 engage in a protein-protein interaction that controls phage infectivity. These results add to the limited evidence for domain swapping in the evolution of phage structural proteins.

Present address: S. N. Winogradsky Institute of Microbiology, Russian Academy of Science, 117312 Moscow, Russia.

Present address: Centre de Biochimie Structurale, CNRS-UMR 9955, INSERM-U554, Universite de Montpellier I, F-34090 Montpellier, France.

Present address: Départment de Biochimie Médicale, University Medical Centre, 1211 Geneva 4, Switzerland.

This article has been cited by other articles:

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