Pathogenic bacteria are becoming increasingly resistant to antibiotics. Alternatives must be found and validated to avoid falling back into the pre-antibiotic era. The use of bacteriophages, natural enemies of bacteria, is one of the most promising alternatives, both in agriculture/veterinary medicine and in human health. Sixty percent of known phages consist of a capsid protecting the viral DNA and a long flexible tail, which serves to recognise the host via one or more receptor binding proteins (RBPs) located at the tip of the tail. The RBP-receptor interaction triggers the infection: opening of the capsid, perforation of the bacterial wall and injection of the viral DNA into the host cytoplasm. Once injected, the viral DNA takes control of the bacterium and converts it into a phage factory; the cycle ends with the explosion of the bacterium and the release of hundreds of new virions.
In this study, researchers at IRIG unveiled the infection of the bacterium E. coli by bacteriophage T5. This infection is initiated by the irreversible binding of T5 RBP pb5 to its bacterial receptor, an E. coli outer membrane iron transporter, FhuA. Thanks to advanced electron microscopy, both in terms of microscopes and cameras, as well as in software for the analysis of the images obtained, the scientists were able to determine the structure of T5 tail tip before and after interaction with FhuA reconstituted in a small membrane patch (nanodisc), as well as the structure of the FhuA-pb5 complex. These structures at atomic resolution allowed to understand how the interaction between pb5 and FhuA, i.e. the recognition of the host by the phage triggers the infection process. Moreover, it details the molecular mechanisms involved in the different steps, from the interaction between the phage and its bacterial receptor, to the perforation of the host's external membrane, including the opening of the phage tail and its anchoring to the membrane.
These studies will contribute to better control and use in health, biotechnology etc…, of these fascinating bacteriophage nanomachines.
Molecular mechanism of the trigger of infection of E. coli
by bacteriophage T5. Credit CEA
Structures of phage T5 tail tip before (1) and after (2) interaction with FhuA are shown in ribbon. On either side, negative stain images of phage T5 isolated (3) and interacting with a minicell (4). (5): T5 phage tail interacting with FhuA in a nanodisc.
Below are detailed the steps of the molecular mechanism, indicated in red or by arrows, from the recognition of the host by the phage to the opening of the phage tail, its anchorage to the membrane and the perforation of the latter.
OM: Outer-membrane, PG: Peptidoglycan