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PLoS One. 2016 Feb 16;11(2):e0149337. doi: 10.1371/journal.pone.0149337. eCollection 2016.

Structure of a Bacterial Virus DNA-Injection Protein Complex Reveals a Decameric Assembly with a Constricted Molecular Channel.

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Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, Kansas, United States of America.
National Resource for Automated Molecular Microscopy, The Scripps Research Institute, La Jolla, California, United States of America.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, 14 2575 Sand Hill Road, MS69, Menlo Park, California, United States of America.


The multi-layered cell envelope structure of Gram-negative bacteria represents significant physical and chemical barriers for short-tailed phages to inject phage DNA into the host cytoplasm. Here we show that a DNA-injection protein of bacteriophage Sf6, gp12, forms a 465-kDa, decameric assembly in vitro. The electron microscopic structure of the gp12 assembly shows a ~150-Å, mushroom-like architecture consisting of a crown domain and a tube-like domain, which embraces a 25-Å-wide channel that could precisely accommodate dsDNA. The constricted channel suggests that gp12 mediates rapid, uni-directional injection of phage DNA into host cells by providing a molecular conduit for DNA translocation. The assembly exhibits a 10-fold symmetry, which may be a common feature among DNA-injection proteins of P22-like phages and may suggest a symmetry mismatch with respect to the 6-fold symmetric phage tail. The gp12 monomer is highly flexible in solution, supporting a mechanism for translocation of the protein through the conduit of the phage tail toward the host cell envelope, where it assembles into a DNA-injection device.

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