Structure of the O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. manihotis GSPB 2755 and GSPB 2364

The O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. manihotis strains GSPB 2755 and GSPB 2364 was studied by sugar and methylation analyses and 1H and 13C NMR spectroscopy, including 2D COSY, TOCSY, NOESY, and H-detected 1H, 13C heteronuclear multiple-quantum coherence (HMQC) experiments. The polysaccharide was found to contain L-rhamnose and L-xylose in the ratio 3:1, and the following structure of the tetrasaccharide repeating unit was established: [formula: see text]     

Shared and unique roles of CAP23 and GAP43 in actin regulation, neurite outgrowth, and anatomical plasticity

CAP23 is a major cortical cytoskeleton-associated and calmodulin binding protein that is widely and abundantly expressed during development, maintained in selected brain structures in the adult, and reinduced during nerve regeneration. Overexpression of CAP23 in adult neurons of transgenic mice promotes nerve sprouting, but the role of this protein in process outgrowth was not clear. Here, we show that CAP23 is functionally related to GAP43, and plays a critical role to regulate nerve sprouting and the actin cytoskeleton. Knockout mice lacking CAP23 exhibited a pronounced and complex phenotype, including a defect to produce stimulus-induced nerve sprouting at the adult neuromuscular junction. This sprouting deficit was rescued by transgenic overexpression of either CAP23 or GAP43 in adult motoneurons. Knockin mice expressing GAP43 instead of CAP23 were essentially normal, indicating that, although these proteins do not share homologous sequences, GAP43 can functionally substitute for CAP23 in vivo. Cultured sensory neurons lacking CAP23 exhibited striking alterations in neurite outgrowth that were phenocopied by low doses of cytochalasin D. A detailed analysis of such cultures revealed common and unique functions of CAP23 and GAP43 on the actin cytoskeleton and neurite outgrowth. The results provide compelling experimental evidence for the notion that CAP23 and GAP43 are functionally related intrinsic determinants of anatomical plasticity, and suggest that these proteins function by locally promoting subplasmalemmal actin cytoskeleton accumulation.     

Suppression of Drosophila cellular immunity by directed expression of the ExoS toxin GAP domain of Pseudomonas aeruginosa

We show here that transgenic Drosophila can be used to decipher the effect of a bacterial toxin on innate immunity and demonstrate the contribution of blood cells in fly resistance to bacterial infection. ExoS is a Pseudomonas aeruginosa exotoxin directly translocated into the host cell cytoplasm through the type III secretion system found in many Gram-negative bacteria. It contains a N-terminal GTPase activating (GAP) domain that prevents cytoskeleton reorganization by Rho family of GTPases in cell culture. Directed expression of the ExoS GAP domain (ExoSGAP) during fly eye morphogenesis inhibited Rac1-, Cdc42- and Rho-dependent signalling, demonstrating for the first time its activity on RhoGTPases in a whole organism. We further showed that fly resistance to P. aeruginosa infections was altered when ExoSGAP was expressed either ubiquitously or in haemocytes, but not when expressed into the fat body, the major source of NF-(kappa)B-dependent anti-microbial peptide synthesis. Fly sensitivity to infection was also observed with Gram-positive Staphylococcus aureus strain and was associated to a reduced phagocytosis capacity of ExoSGAP-expressing haemocytes. Our results highlight the major contribution of cellular immunity during the first hours after Drosophila infection by P. aeruginosa, an opportunist pathogen affecting patients with pathologies associated to a reduced leukocyte number.     

Adhesion of enterotoxigenic Escherichia coli to immobolized intestinal mucosal preparations: a model for adhesion to mucosal surface components

The ability of enterotoxigenic strains of E. coli to adhere to immobilized mucosal components prepared from the large and small intestines of mice was examined in vitro. Various strains of E. coli were labeled with (³H)-acetate and incubated in tissue culture plates containing immobilized mucosal components or bovine serum albumin. E. coli strains which were positive for K88 or K99 antigen, and one E. coli strain isolated from a human urinary tract infection, were shown to adhere readily to large and small intestinal mucosal preparations, but not to bovine serum albumin. E. coli K-12 and a variety of enterotoxigenic strains isolated from humans, including a CFA/1 positive strain, demonstrated little or no ability to adhere to any of the preparations. E. coli adhesion to the mucosal preparations was shown to be mannose-resistant for all E. coli strains tested, but was inhibited by growth of the organisms at 18°C. Adhesion of each of the K88 or K99 positive strains was inhibited by homologous antiserum, but not by heterologous antiserum or normal rabbit serum. The data indicate that the mucosal preparations employed contain receptors for specific bacterial adhesins, and suggest that the use of such preparations may provide an alternative to the use of whole cells both as a source of receptor and as a means of investigating the adhesive properties of E. coli.     

An Interactive Network of Elastase,Secretases, and PAR-2 Protein Regulates CXCR1 Receptor Surface Expression on Neutrophils

CXCL8 (IL-8) recruits and activates neutrophils through the G protein-coupled chemokine receptor CXCR1. We showed previously that elastase cleaves CXCR1 and thereby impairs antibacterial host defense. However, the molecular intracellular machinery involved in this process remained undefined. Here we demonstrate by using flow cytometry, confocal microscopy, subcellular fractionation, co-immunoprecipitation, and bioluminescence resonance energy transfer that combined α- and γ-secretase activities are functionally involved in elastase-mediated regulation of CXCR1 surface expression on human neutrophils, whereas matrix metalloproteases are dispensable. We further demonstrate that PAR-2 is stored in mobilizable compartments in neutrophils. Bioluminescence resonance energy transfer and co-immunoprecipitation studies showed that secretases, PAR-2, and CXCR1 colocalize and physically interact in a novel protease/secretase-chemokine receptor network. PAR-2 blocking experiments provided evidence that elastase increased intracellular presenilin-1 expression through PAR-2 signaling. When viewed in combination, these studies establish a novel functional network of elastase, secretases, and PAR-2 that regulate CXCR1 expression on neutrophils. Interfering with this network could lead to novel therapeutic approaches in neutrophilic diseases, such as cystic fibrosis or rheumatoid arthritis.     

Natural Polymorphisms in Tap2 Influence Negative Selection and CD4∶CD8 Lineage Commitment in the Rat

Genetic variation in the major histocompatibility complex (MHC) affects CD4∶CD8 lineage commitment and MHC expression. However, the contribution of specific genes in this gene-dense region has not yet been resolved. Nor has it been established whether the same genes regulate MHC expression and T cell selection. Here, we assessed the impact of natural genetic variation on MHC expression and CD4∶CD8 lineage commitment using two genetic models in the rat. First, we mapped Quantitative Trait Loci (QTLs) associated with variation in MHC class I and II protein expression and the CD4∶CD8 T cell ratio in outbred Heterogeneous Stock rats. We identified 10 QTLs across the genome and found that QTLs for the individual traits colocalized within a region spanning the MHC. To identify the genes underlying these overlapping QTLs, we generated a large panel of MHC-recombinant congenic strains, and refined the QTLs to two adjacent intervals of ∼0.25 Mb in the MHC-I and II regions, respectively. An interaction between these intervals affected MHC class I expression as well as negative selection and lineage commitment of CD8 single-positive (SP) thymocytes. We mapped this effect to the transporter associated with antigen processing 2 (Tap2) in the MHC-II region and the classical MHC class I gene(s) (RT1-A) in the MHC-I region. This interaction was revealed by a recombination between RT1-A and Tap2, which occurred in 0.2% of the rats. Variants of Tap2 have previously been shown to influence the antigenicity of MHC class I molecules by altering the MHC class I ligandome. Our results show that a restricted peptide repertoire on MHC class I molecules leads to reduced negative selection of CD8SP cells. To our knowledge, this is the first study showing how a recombination between natural alleles of genes in the MHC influences lineage commitment of T cells.     

Salmonella enterica Flagellin Is Recognized via FLS2 and Activates PAMP-Triggered Immunity in Arabidopsis thaliana

Infections with Salmonella enterica belong to the most prominent causes of food poisoning and infected fruits and vegetables represent important vectors for salmonellosis. Recent evidence indicates that plants recognize S. enterica and raise defense responses. Nonetheless, the molecular mechanisms controlling the interaction of S. enterica with plants are still largely unclear. Here, we show that flagellin from S. enterica represents a prominent pathogenassociated molecular pattern （PAMP） in Arabidopsis thaliana, which induces PAMP-triggered immunity （PTI） via the recognition of the fig22 domain by the receptor kinase FLS2. The Arabidopsis fls2 mutant shows reduced though not abolished PTI activation, indicating that plants rely also on recognition of other S. enterica PAMPs. Interestingly, the S. enterica type III secretion system （T3SS） mutant prgH- induced stronger defense gene expression than wild-type bacteria in Arabidopsis, suggesting that T3SS effectors are involved in defense suppression. Furthermore, we observe that S. enterica strains show variation in the fig22 epitope, which results in proteins with reduced PTI-inducing activity. Altogether, these results show that S. enterica activates PTI in Arabidopsis and suggest that, in order to accomplish plant colonization, S. enterica evolved strategies to avoid or suppress PTI.