Structure of the bacteriophage T4 baseplate

Petr Gennadievich Leiman, Purdue University

Abstract

My Ph.D. research involved studying the process of infection of Escherichia coli bacteria by bacteriophage T4. Bacteriophage T4 is a large, double-stranded DNA, tailed virus belonging to the Myoviridae subfamily. The bacteriophage T4 tail is composed of two concentric cylinders: the inner rigid tail tube and the outer contractile tail sheath. One end of the tail is associated with the unique portal vertex of the head capsid, whereas the other end is terminated with a baseplate to which the fibers are attached. The baseplate and fibers are responsible for host cell recognition and attachment of the phage to the cell surface. Upon interaction of the fibers with the lipopolysaccharides on the cell surface, the baseplate changes its conformation from hexagonal to star-shaped triggering tail sheath contraction. The contracting tail sheath drives the tail tube through the cell envelope bringing the tube into contact with the inner cell membrane, which initiates release of the phage DNA into the host. Structure of the bacteriophage T4 baseplate has been investigated using electron cryo-microscopy and X-ray crystallography of the component proteins. The crystal structures of six baseplate proteins, four of which are reported in this work, were fitted into a 12 Å resolution three-dimensional reconstruction of the baseplate in the hexagonal conformation. A 17 Å resolution reconstruction of the star-shaped baseplate was also obtained and interpreted in terms of the component proteins. The baseplate appeared to be stabilized in the hexagonal conformation by the six short tail fibers, which are folded under the baseplate in a garland-like arrangement with the help of the short tail fiber-attachment protein, gene product (gp) 11. In the star conformation, gp11 was found to dissociate from the short tail fibers and bind to the long tail fibers. Upon binding to the cell surface receptors, the carboxy terminal, receptor-binding domains of the short tail fibers become free and disengage from the garland, thus unlocking the baseplate structure. The long tail fibers associate with gp11 and switch the baseplate to the star conformation, which initiates tail sheath contraction.

Degree

Ph.D.

Advisors

Rossmann, Purdue University.

Subject Area

Molecular biology|Biophysics

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