J Bacteriol 2006,188(7):2309–2324.PubMedCrossRef 63. Beare PA: Genetic manipulation of Coxiella burnetii . Adv Exp Med Biol 2012, 984:249–271.PubMedCrossRef 64. Seshadri R, Hendrix LR, Samuel JE: Differential expression of translational elements by life cycle variants of Coxiella burnetii . Infect Immun 1999,67(11):6026–6033.PubMed Competing interests The authors declare they have no competing interests. Authors’ contributions CMS designed and conducted experiments and

drafted the manuscript. AO conceived the study and conducted experiments. PAB constructed the expression vector and assisted with cloning. KMS carried out EM experiments. RAH participated in study Selleckchem BVD-523 design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.”
“Background Bacterial pathogens exploit host niches using strategies that block or modify host defense pathways. One such strategy employed by the Gram-negative bacterium Salmonella

enterica, is the translocation XAV-939 mouse of effector proteins into the host cell through a type three secretion system (T3SS). S. enterica serovar Typhimurium (S. Typhimurium) has two T3SSs encoded within Salmonella pathogenicity island-1 (SPI-1) and SPI-2 that facilitate invasion and intracellular survival within host cells [1–3]. The assembly of the T3SS is complex, involving the formation of membrane channels in the bacterial inner and outer membrane, and a terminal translocon that forms a pore in host membranes. Both SPI-1 and SPI-2 encode a distinct group of chaperones that bind to their cognate cargo proteins to coordinate T3SS assembly and secretion of effectors. Virulence chaperones belong to one of three defined classes [4]: class I chaperones bind to single (IA) or multiple (IB) effectors, class II chaperones interact with translocon components, filipin and class III chaperones partner with apparatus components.

Among each of the different classes, chaperones share structural similarity yet their amino acid sequence can be poorly conserved. As such, many chaperones have been first identified based on low sequence identity with previously characterized proteins, and by shared physical properties such as isoelectric point (pI). Class I chaperones tend to be small proteins (~9-15 kDa) with acidic pI, and function as dimers adopting a horseshoe-like shape [5–7]. Class II chaperones also form dimers but do not have an acidic pI, which reflects a different interaction surface required for substrate binding [8, 9]. In addition to directing secretion events, chaperone-cargo pairs can function as regulatory proteins for T3SS gene expression [10]. The FlgN chaperone interacts with FlgK-FlgL to form a repressive complex that inhibits expression of late flagellar genes [11].