3RWN: Atomic structure of bacteriophage sf6 tail needle knob

Podoviridae are double-stranded DNA bacteriophages that use short, non-contractile tails to adsorb to the host cell surface. Within the tail apparatus of P22-like phages, a dedicated fiber known as the "tail needle" likely functions as a cell envelope-penetrating device to promote ejection of viral DNA inside the host. In Sf6, a P22-like phage that infects Shigella flexneri, the tail needle presents a C-terminal globular knob. This knob, absent in phage P22 but shared in other members of the P22-like genus, represents the outermost exposed tip of the virion that contacts the host cell surface. Here, we report a crystal structure of the Sf6 tail needle knob determined at 1.0 A resolution. The structure reveals a trimeric globular domain of the TNF fold structurally superimposable with that of the tail-less phage PRD1 spike protein P5 and the adenovirus knob, domains that in both viruses function in receptor binding. However, P22-like phages are not known to utilize a protein receptor and are thought to directly penetrate the host surface. At 1.0 A resolution, we identified three equivalents of l-glutamic acid (l-Glu) bound to each subunit interface. Although intimately bound to the protein, l-Glu does not increase the structural stability of the trimer nor it affects its ability to self-trimerize in vitro. In analogy to P22 gp26, we suggest the tail needle of phage Sf6 is ejected through the bacterial cell envelope during infection and its C-terminal knob is threaded through peptidoglycan pores formed by glycan strands.
PDB ID: 3RWNDownload
MMDB ID: 91269
PDB Deposition Date: 2011/5/9
Updated in MMDB: 2018/07
Experimental Method:
x-ray diffraction
Resolution: 1  Å
Source Organism:
Similar Structures:
Biological Unit for 3RWN: trimeric; determined by author and by software (PISA)
Molecular Components in 3RWN
Label Count Molecule
Proteins (3 molecules)
Gene 9 Protein
Molecule annotation
Chemicals (4 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB