Virion Structure and Mechanism of Genome Delivery of Bacteriophage SU10
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|Bacteriophages are molecular machines evolved to infect cells. Historically bacteriophages from the family Podoviridae were characterised by short non-contractile tails. Here we present the structure of native and genome releasing virion of phage SU10. SU10 has a prolate capsid with a dodecameric portal complex that features a prolonged crown-barrel. The tail of SU10 is decorated by long and short tail fibers, both present in six copies. Tail needle protrudes out from the center of the base plate. Our observations by CryoEM allows us to propose mechanism of the early stages of the phage infection. SU10 binds to the cell surface by primary and secondary receptor binding proteins. Primary receptor binding proteins, which bind reversibly, are located at distal ends of the long tail fibres. After primary receptor recognition, short tail fibres flip towards the cell surface. C-terminal receptor binding domains of short tail fibres serve as secondary irreversible receptor binding proteins. Extended nozzle is formed by a remodeled tail complex together with flipped short tail fibres. During attachment of secondary receptor binding proteins the tail needle mechanically disrupts the outer cell membrane and dissociates from the virion. Phage core proteins are ejected from the capsid and form a translocation channel. Transglycosylase domains, which are located on the outer surface of the translocation channel, hydrolytically degrade the cell wall. Translocation channel together with extended nozzle serve as a tunnel for phage DNA delivery into the bacterial cytoplasm. Our study reveals major structural changes of podovirus tail upon phage attachment on the cell surface were not observed up to date.