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Publication Abstract from PubMed

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. Though 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 two hundred 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 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 post-ejection trimer-of-hairpins that form 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.

Structural plasticity of the protein plug that traps newly packaged genomes in podoviridae virions.,Bhardwaj A, Sankhala RS, Olia AS, Brooke D, Casjens SR, Taylor DJ, Prevelige PE Jr, Cingolani G J Biol Chem. 2015 Nov 16. pii: jbc.M115.696260. PMID:26574546^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.