Protein-protein interactions in filamentous bacteriophage infection of Pseudomonas aeruginosa

• Main Author: Holland, S. J.
• Published: University of Cambridge 2003
• Subjects: 571.29
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604161

The infection mechanism of the filamentous bacteriophages Pf1 and Pf3, specific to <i>Pseudomonas aeruginosa</i>, has not been studied. These virions differ in their DNA packaging, but their protein capsids share the same helical symmetry. Bacteriophage Pf3 has been reported to bind to the sides rather than the tip of its host pili, the pili of plasmid RP4, but this and other aspects of its biology have remained somewhat confused. This thesis describes work that addresses protein-protein interactions involved in the process of infection of <i>P. aeruginosa</i>. RP4 pili have been purified from plasmids expressed in <i>E. coli</i> and their structure examined by electron microscopy and X-ray fibre diffraction, which has given new insights into the pilus structure. The expression of RP4 pili in <i>E. coli</i> has also allowed an investigation into the pilus specificity and host range of bacteriophage Pf3. It was shown to be specific for, and to bind to the shaft of, the RP4 pilus and to be capable of infecting <i>E. coli</i> expressing this pilus, although production of Pf3 bacteriophage virions by <i>E. coli</i> is much slower than that observed for the natural host, <i>P. aeruginosa</i> PAO. The interaction of the Pf3 virion with the pilus was shown to involve a minor coat protein that serves as the counterpart of the g3p in the Ff virion. A sub-gene encoding C-terminally truncated construct of this protein was cloned from Pf3 RF DNA and over expressed in <i>E. coli</i>. When tested for pilus specificity, it was confirmed as the major globular part of the pilus adsorption protein of bacteriophage Pf3. The ability of bacteriophages Pf1 and Pf3 and their respective g3p proteins to interact with the TolA protein of <i>P. aeruginosa </i>was investigated. Both types of virion were found to interact with domain II of TolA and the g3p of Pfl to interact with TolA domain III. This differs significantly from what has hitherto been reported for the infection of <i>E. coli</i> by Ff bacteriophage.