5BU8: Hk620 Tail Needle Crystallized At Ph 7.5 And Derivatized With Xenon

Bacterial viruses of the P22-like family encode a specialized tail needle essential for genome stabilization after DNA packaging and implicated in Gram-negative cell envelope penetration. The atomic structure of P22 tail needle (gp26) crystallized at acidic pH reveals a slender fiber containing an N-terminal "trimer of hairpins" tip. Although the length and composition of tail needles vary significantly in Podoviridae, unexpectedly, the amino acid sequence of the N-terminal tip is exceptionally conserved in more than 200 genomes of P22-like phages and prophages. In this paper, we used x-ray crystallography and EM to investigate the neutral pH structure of three tail needles from bacteriophage P22, HK620, and Sf6. In all cases, we found that the N-terminal tip is poorly structured, in stark contrast to the compact trimer of hairpins seen in gp26 crystallized at acidic pH. Hydrogen-deuterium exchange mass spectrometry, limited proteolysis, circular dichroism spectroscopy, and gel filtration chromatography revealed that the N-terminal tip is highly dynamic in solution and unlikely to adopt a stable trimeric conformation at physiological pH. This is supported by the cryo-EM reconstruction of P22 mature virion tail, where the density of gp26 N-terminal tip is incompatible with a trimer of hairpins. We propose the tail needle N-terminal tip exists in two conformations: a pre-ejection extended conformation, which seals the portal vertex after genome packaging, and a postejection trimer of hairpins, which forms upon its release from the virion. The conformational plasticity of the tail needle N-terminal tip is built in the amino acid sequence, explaining its extraordinary conservation in nature.
PDB ID: 5BU8Download
MMDB ID: 134412
PDB Deposition Date: 2015/6/3
Updated in MMDB: 2015/12
Experimental Method:
x-ray diffraction
Resolution: 2.2  Å
Source Organism:
Similar Structures:
Biological Unit for 5BU8: monomeric; determined by author
Molecular Components in 5BU8
Label Count Molecule
Protein (1 molecule)
DNA Stabilization Protein
Molecule annotation
Chemicals (5 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB