Structural basis for host recognition and superinfection exclusion by bacteriophage T5

Area of Science:

• Structural Biology
• Microbiology
• Virology

Background:

• Bacteriophage infection involves receptor binding proteins (RBPs) attaching to host cell receptors.
• Superinfection exclusion (SE) proteins prevent secondary infections by modulating host receptors, but their mechanism is unclear.
• Understanding these interactions is crucial for controlling phage infections and phage therapy.

Purpose of the Study:

• To elucidate the structural basis of phage T5 receptor FhuA interaction with its RBP (pb5) and the SE lipoprotein (Llp).
• To understand the mechanism by which SE proteins like Llp prevent phage T5 infection of Escherichia coli.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) was used to determine the structure of FhuA in complex with T5 RBP pb5.
• X-ray crystallography was employed to obtain the structure of FhuA complexed with the SE lipoprotein Llp.
• Structural analysis focused on the binding interfaces and conformational changes induced in FhuA.

Main Results:

• The T5 RBP pb5 inserts loops into the FhuA lumen, contacting the plug but not altering receptor conformation.
• The SE lipoprotein Llp binds to a nonnative FhuA plug conformation, inducing inward folding of extracellular loops via reverse allostery.
• Llp binding to FhuA blocks the pb5 binding site, explaining the inhibition of phage T5 infection.

Conclusions:

• Phage DNA translocation likely does not occur through the lumen of outer membrane channels.
• SE lipoproteins like Llp can inhibit phage infection by jamming TonB-dependent transporters through structural modulation.
• This study provides a structural mechanism for superinfection exclusion mediated by small phage lipoproteins.