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Nat Struct Mol Biol. 2015 May;22(5):377-82. doi: 10.1038/nsmb.2995. Epub 2015 Mar 30.

Atomic structures of a bactericidal contractile nanotube in its pre- and postcontraction states.

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1] Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles (UCLA), Los Angeles, California, USA. [2] California NanoSystems Institute (CNSI), UCLA, Los Angeles, California, USA.
AvidBiotics, South San Francisco, California, USA.
cole Polytechnique Fédérale de Lausanne (EPFL), Institute of Physics of Biological Systems, Lausanne, Switzerland.


R-type pyocins are representatives of contractile ejection systems, a class of biological nanomachines that includes, among others, the bacterial type VI secretion system (T6SS) and contractile bacteriophage tails. We report atomic models of the Pseudomonas aeruginosa precontraction pyocin sheath and tube, and the postcontraction sheath, obtained by cryo-EM at 3.5-Å and 3.9-Å resolutions, respectively. The central channel of the tube is negatively charged, in contrast to the neutral and positive counterparts in T6SSs and phage tails. The sheath is interwoven by long N- and C-terminal extension arms emanating from each subunit, which create an extensive two-dimensional mesh that has the same connectivity in the extended and contracted state of the sheath. We propose that the contraction process draws energy from electrostatic and shape complementarities to insert the inner tube through bacterial cell membranes to eventually kill the bacteria.

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