Structural investigations of a Podoviridae streptococcus phage C1, implications for the mechanism of viral entry

Abstract

The Podoviridae phage C1 was one of the earliest isolated bacteriophages and the first virus documented to be active against streptococci. The icosahedral and asymmetric reconstructions of the virus were calculated using cryo-electron microscopy. The capsid protein has an HK97 fold arranged into a T ¼ 4 icosahedral lattice. The C1 tail is terminated with a φ29-like knob, surrounded by a skirt of twelve long appendages with novel morphology. Several C1 structural proteins have been identified, including a candidate for an appendage. The crystal structure of the knob has an N-terminal domain with a fold observed previously in tube forming proteins of Siphoviridae and Myoviridae phages. The structure of C1 suggests the mechanisms by which the virus digests the cell wall and ejects its genome. Although there is little sequence similarity to other phages, conservation of the structural proteins demonstrates a common origin of the head and tail, but more recent evolution of the appendages.bacteriophage C1 tail | tail knob | X-ray crystallography

Structure and genome release of Twort-like Myoviridae phage with a double-layered baseplate

“…Thus, domain I is required to hold domain II in position so that it can form interactions within the tail sheath protein hexamer. In contrast, domains I and II of the T4 tail sheath protein are located parallel to each other with a limited contact interface, and domain I was proposed to be dispensable for tail sheath formation (13,18,28,29). Domain III of the phi812 tail sheath protein interacts with domain IV from a tail sheath protein positioned toward the baseplate (Fig.…”

Molecular architecture of tailed double-stranded DNA phages

“…85 The C1_gp12 (573 residues) protein is composed of 4 domains, with the N-terminal domain, binding to the dodecameric uppertube protein. The N-terminal domain C1_gp12 (120 residues) has a fold similar to the tail-tube proteins of the Siphoviridae and Myoviridae phages showing evolutionary ties between the short and long phage tails.…”

“…The N-terminal domain C1_gp12 (120 residues) has a fold similar to the tail-tube proteins of the Siphoviridae and Myoviridae phages showing evolutionary ties between the short and long phage tails. 85 Podophages may contain different proteins bound at the end of their tail tubes. For example, phage φ29 has 2 copies of the peptidoglycan-degrading protein, gp13 (365 residues) at the very tip of its tail.…”

“…The asymmetric reconstruction of the podophage C1, which does not have an internal capsid core, is also consistent with the spool model. 85 A spool model was also proposed for phage T4, although the axis of the spool was perpendicular to the axis of the tail. 117 The spool model, however, does not always apply to the capsids without internal cores.…”

Membrane Penetration by Bacterial Viruses

“…These common features imply the possible convergent evolution of eukaryotic and prokaryotic viruses in response to a similar barrier, the cell membrane. Although the bacteriophage C1 contains a tail protein, gp12, that assembles to form a similar hexameric tube structure, the sequence similarity between 29 gp9 and C1 gp12 is low (42). Based on structure and sequence information, a similar long loop can also be mapped on the C1 gp12 sequence.…”