title: Three-dimensional structure of the toxin-delivery particle antifeeding prophage of Serratia entomophila.
abstract: The Serratia entomophila antifeeding prophage (Afp) is a bullet-shaped toxin-delivery apparatus similar to the R-pyocins of Pseudomonas aeruginosa. Morphologically it resembles the sheathed tail of bacteriophages such as T4, including a baseplate at one end. It also shares features with the type VI secretion systems. Cryo-electron micrographs of tilted Afp specimens (up to 60 degrees) were analyzed to determine the correct cyclic symmetry to overcome the limitation imposed by exclusively side views in nominally untilted specimens. An asymmetric reconstruction shows clear 6-fold cyclic symmetry contrary to a previous conclusion of 4-fold symmetry based on analysis of only the preferred side views (Sen, A., Rybakova, D., Hurst, M. R., and Mitra, A. K. (2010) J. Bacteriol. 192, 4522-4525). Electron tomography of negatively stained Afp revealed right-handed helical striations in many of the particles, establishing the correct hand. Higher quality micrographs of untilted specimens were processed to produce a reconstruction at 2.0-nm resolution with imposed 6-fold symmetry. The helical parameters of the sheath were determined to be 8.14 nm for the subunit rise along and 40.5° for the rotation angle around the helix. The sheath is similar to that of the T4 phage tail but with a different arrangement of the subdomain of the polymerizing sheath protein(s). The central tube is similar to the diameter and axial width of the Hcp1 hexamer of P. aeruginosa type VI secretion system. The tube extends through the baseplate into a needle resembling the "puncture device" of the T4 tail. The tube contains density that may be the toxin and/or a length-determining protein.
authors.affiliation: From the NIAMS, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: J Bernard
authors.initials: JB
authors.lastname: Heymann
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand, and.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Bartho
authors.affiliation: Innovative Farm Systems, Agresearch, Lincoln, Christchurch 8140, New Zealand.
authors.forename: Daria
authors.initials: D
authors.lastname: Rybakova
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand, and.
authors.forename: Hari P
authors.initials: HP
authors.lastname: Venugopal
authors.affiliation: From the NIAMS, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Winkler
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand, and.
authors.forename: Anindito
authors.initials: A
authors.lastname: Sen
authors.affiliation: Innovative Farm Systems, Agresearch, Lincoln, Christchurch 8140, New Zealand.
authors.forename: Mark R H
authors.initials: MRH
authors.lastname: Hurst
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland 1142, New Zealand, and. Electronic address: a.mitra@auckland.ac.nz.
authors.forename: Alok K
authors.initials: AK
authors.lastname: Mitra
mesh_terms: D058947:Bacterial Secretion Systems / Q000502:physiology; D001435:Bacteriophages / Q000378:metabolism / Q000648:ultrastructure*; D012705:Serratia / Q000378:metabolism / Q000821:virology*
chemical_list: D058947:Bacterial Secretion Systems
keywords: Bacterial Pathogenesis; Bacteriophage Tail Sheath; Cryo-electron Microscopy; Electron Microscopy (EM); Electron Tomography; Negative Stain Tomography; Single Particle Analysis; Structural Biology