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J Biol Chem. 2016 Jan 1;291(1):215-26. doi: 10.1074/jbc.M115.696260. Epub 2015 Nov 16.

Structural Plasticity of the Protein Plug That Traps Newly Packaged Genomes in Podoviridae Virions.

Author information

1
From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
2
the Department of Biochemistry & Biophysics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104.
3
the Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294.
4
the Division of Microbiology and Immunology, Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah 84112.
5
the Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106, and.
6
From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, the Institute of Biomembranes and Bioenergetics, National Research Council, 70126 Bari, Italy gino.cingolani@jefferson.edu.

Abstract

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.

KEYWORDS:

DNA packaging; bacteriophage; hydrogen-deuterium exchange; infection; protein folding; tail needle; trimer of hairpins; viral genome ejection; x-ray crystallography

PMID:
26574546
PMCID:
PMC4697157
DOI:
10.1074/jbc.M115.696260
[Indexed for MEDLINE]
Free PMC Article

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