Summary paragraphBacteria have developed mechanisms to communicate and compete with one another in diverse environments 1. A new form of intercellular communication, contact-dependent growth inhibition (CDI), was discovered recently in Escherichia coli 2. CDI is mediated by the CdiB/CdiA two-partner secretion system. CdiB facilitates secretion of the CdiA ‘exoprotein’ onto the cell surface. An additional immunity protein (CdiI) protects CDI+ cells from autoinhibition 2, 3. The mechanisms by which CDI blocks cell growth and CdiI counteracts this growth arrest are unknown. Moreover, the existence of CDI activity in other bacteria has not been explored. Here we show that the CDI growth inhibitory activity resides within the carboxy-terminal region of CdiA (CdiA-CT), and that CdiI binds and inactivates cognate CdiA-CT, but not heterologous CdiA-CT. Bioinformatic and experimental analyses show that multiple bacterial species encode functional CDI systems with high sequence variability in the CdiA-CT and CdiI coding regions. CdiA-CT heterogeneity implies that a range of toxic activities are utilized during CDI. Indeed, CdiA-CTs from uropathogenic E. coli and the plant pathogen Dickeya dadantii have different nuclease activities, each providing a distinct mechanism of growth inhibition. Finally, we show that bacteria lacking the CdiA-CT and CdiI coding regions are unable to compete with isogenic wild-type CDI+ cells in both laboratory media and upon a eukaryotic host. Taken together, these results suggest that CDI systems constitute an intricate immunity network that plays an important role in bacterial competition.

Summary Histidine-rich glycoprotein (HRG) is an abundant plasma glycoprotein that has a multidomain structure, interacts with many ligands, and has been shown to regulate a number of important biological processes. HRG ligands include Zn 2+ and haem, tropomyosin, heparin and heparan sulphate, plasminogen, plasmin, fibrinogen, thrombospondin, IgG, Fc γ R and complement. In many cases, the histidine-rich region of the molecule enhances ligand binding following interaction with Zn 2+ or exposure to low pH, conditions associated with sites of tissue injury or tumour growth. The multidomain nature of HRG indicates that it can act as an extracellular adaptor protein, bringing together disparate ligands, particularly on cell surfaces. HRG binds to most cells primarily via heparan sulphate proteoglycans, binding which is also potentiated by elevated free Zn 2+ levels and low pH. Recent reports have shown that HRG can modulate angiogenesis and additional studies have shown that it may regulate other physiological processes such as cell adhesion and migration, fibrinolysis and coagulation, complement activation, immune complex clearance and phagocytosis of apoptotic cells. This review outlines the molecular, structural, biological and clinical properties of HRG as well as describing the role of HRG in various physiological processes.

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Histidine-rich glycoprotein (HRG) is an

SummaryTo investigate the mechanism by which the Bordetella BvgAS phosphorelay controls expression of at least three distinct phenotypic phases, we isolated and characterized two B. pertussis mutants that were able to express Bvg -and Bvg i phase phenotypes but not Bvg + + + + phase phenotypes. In both cases, the mutant phenotype was due to a single nucleotide change in bvgA resulting in a single amino acid substitution in BvgA. In vitro phosphorylation assays showed that BvgA containing the T194M substitution was significantly impaired in its ability to use either BvgS or acetyl phosphate as a substrate for phosphorylation. Binding studies indicated that this mutant protein was able to bind an oligonucleotide containing a highaffinity BvgA binding site in a manner similar to wildtype BvgA, but was defective for binding the fhaB promoter in the absence of RNA polymerase (RNAP). By contrast, BvgA containing the R152H substitution had wild-type phosphorylation properties but was severely defective in its ability to bind either the highaffinity BvgA binding site-containing oligonucleotide or the fhaB promoter by itself. Both mutant BvgA proteins were able to bind the fhaB promoter in the presence of RNAP however, demonstrating the profound effect that RNAP has on stabilizing the ternary complexes between promoter DNA, BvgA and RNAP. Our results are consistent with the hypothesis that

Significant uterine growth occurred in normal and hypogonadal (hpg) mice between Days 7 and 21 but thereafter no further growth was observed in hpg mice. The ovaries of hpg mice were significantly smaller than those of normals at all ages, but there was no significant difference between the number of non-growing follicles in the ovaries of mutants and their normal littermates at any age studied, and normal and hpg mice showed a marked reduction in the number of non-growing follicles during the first month of life. The size and composition of the growing follicle population in hpg mice, however, differed markedly from those in normal animals and by 21 days of age the number of growing follicles in mutants was significantly reduced. There was no significant difference in the number of Type 3b follicles before 60 days of age, but the number of all other follicle types was significantly less in hpg mice at all ages studied. Follicles in which the antrum is fully developed (Type 7 and 8) were never seen in the ovaries of mutants and corpora lutea were never observed. Interstitial tissue development was also very poor in hpg ovaries. The hypothalamic GnRH content in normal mice remained low until Day 20, before rising sharply to adult levels (approximately 800 pg) between Days 20 and 30. The pituitary FSH content increased over the first 10 days of life to reach a peak of about 5000 ng, before declining to the adult value of about 2000 ng by Day 30, whilst the plasma FSH concentration was high in the first 10 days, but fell to adult levels over the next 20 days. Pituitary LH content increased significantly between Days 5 and 10 to reach the adult level of about 600 ng. Hypothalamic GnRH was undetectable at all ages in hypogonadal mice, but the pituitary content of FSH and LH had risen to the attenuated mutant adult value by Day 15, and unlike normals, plasma FSH concentrations were not elevated during the neonatal period. These results suggest that minimal gonadotrophic stimulation of the ovary from birth has no effect on the total number of follicles but reduces the number of growing follicles and prevents follicle growth beyond the early antral stage. Gonadotrophins therefore appear to have a role in the initiation and continuance of follicle growth in the adult mouse.

Contact-dependent growth inhibition (CDI) is a mechanism by which bacteria exchange toxins via direct cell-to-cell contact. CDI systems are distributed widely among Gram-negative pathogens and are thought to mediate interstrain competition. Here, we describe tsf mutations that alter the coiled-coil domain of elongation factor Ts (EF-Ts) and confer resistance to the CdiA-CT EC869 tRNase toxin from enterohemorrhagic Escherichia coli EC869. Although EF-Ts is required for toxicity in vivo, our results indicate that it is dispensable for tRNase activity in vitro. We find that CdiA-CT EC869 binds to elongation factor Tu (EF-Tu) with high affinity and this interaction is critical for nuclease activity. Moreover, in vitro tRNase activity is GTP-dependent, suggesting that CdiA-CT EC869 only cleaves tRNA in the context of translationally active GTP·EF-Tu·tRNA ternary complexes. We propose that EF-Ts promotes the formation of GTP·EF-Tu·tRNA ternary complexes, thereby accelerating substrate turnover for rapid depletion of target-cell tRNA.cell communication | protein synthesis | toxin-immunity proteins | ribonuclease | bacterial competition