title: Structural characterization of the molecular platform for type III secretion system assembly.
abstract: Type III secretion systems (TTSSs) are multi-protein macromolecular 'machines' that have a central function in the virulence of many Gram-negative pathogens by directly mediating the secretion and translocation of bacterial proteins (termed effectors) into the cytoplasm of eukaryotic cells. Most of the 20 unique structural components constituting this secretion apparatus are highly conserved among animal and plant pathogens and are also evolutionarily related to proteins in the flagellar-specific export system. Recent electron microscopy experiments have revealed the gross 'needle-shaped' morphology of the TTSS, yet a detailed understanding of the structural characteristics and organization of these protein components within the bacterial membranes is lacking. Here we report the 1.8-A crystal structure of EscJ from enteropathogenic Escherichia coli (EPEC), a member of the YscJ/PrgK family whose oligomerization represents one of the earliest events in TTSS assembly. Crystal packing analysis and molecular modelling indicate that EscJ could form a large 24-subunit 'ring' superstructure with extensive grooves, ridges and electrostatic features. Electron microscopy, labelling and mass spectrometry studies on the orthologous Salmonella typhimurium PrgK within the context of the assembled TTSS support the stoichiometry, membrane association and surface accessibility of the modelled ring. We propose that the YscJ/PrgK protein family functions as an essential molecular platform for TTSS assembly.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia, Canada V6T 1Z3.
authors.forename: Calvin K
authors.initials: CK
authors.lastname: Yip
authors.forename: Tyler G
authors.initials: TG
authors.lastname: Kimbrough
authors.forename: Heather B
authors.initials: HB
authors.lastname: Felise
authors.forename: Marija
authors.initials: M
authors.lastname: Vuckovic
authors.forename: Nikhil A
authors.initials: NA
authors.lastname: Thomas
authors.forename: Richard A
authors.initials: RA
authors.lastname: Pfuetzner
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Frey
authors.forename: B Brett
authors.initials: BB
authors.lastname: Finlay
authors.forename: Samuel I
authors.initials: SI
authors.lastname: Miller
authors.forename: Natalie C J
authors.initials: NC
authors.lastname: Strynadka
mesh_terms: D000595:Amino Acid Sequence; D019921:Biotinylation; D003460:Crystallization; D018360:Crystallography, X-Ray; D019277:Entropy; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D021381:Protein Transport; D012486:Salmonella typhimurium / Q000737:chemistry* / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D055672:Static Electricity
chemical_list: D029968:Escherichia coli Proteins