Abstract
Podophages, a type of tailed bacteriophage with short noncontractile tails, have evolved unique strategies to infect gram-negative bacteria, like the pathogen Pectobacterium. Unlike other phages with longer tails, podophages encode a specialized protein complex called an ejectosome, which is packed within the viral capsid and released during infection [1]. For infection, this complex forms a temporary channel that bridges the bacterial outer and inner membranes, enabling DNA passage across the gram-negative cell wall.
Using single-particle cryo-electron microscopy, we determined the of ΦM1 bacteriophage ejectosome structure at 3.32 Å resolution [2]. This large complex of approximately 1.5 MDa is composed of tetrameric and octameric proteins arranged to fit through the tail narrow opening. The ΦM1 ejectosome is structurally distinct from the only other available ejectosome structure belonging to the model T7 phage. Our study is the first to report interactions between the ejectosome and the viral genomic DNA by showing that DNA spools around the ejectosome before entering the phage tail in a reproducible manner. Furthermore, high-resolution reconstructions of the ΦM1 capsid possesses two highly unusual decoration proteins arranged across the viral capsid which may play dual functional roles in viral infectivity.