Differential regulation of amidase- and formamidase-mediated ammonia production by the Helicobacter pylori fur repressor.

The production of high levels of ammonia allows the human gastric pathogen Helicobacter pylori to survive the acidic conditions in the human stomach. H. pylori produces ammonia through urease-mediated degradation of urea, but it is also able to convert a range of amide substrates into ammonia via its AmiE amidase and AmiF formamidase enzymes. Here data are provided that demonstrate that the iron-responsive regulatory protein Fur directly and indirectly regulates the activity of the two H. pylori amidases. In contrast to other amidase-positive bacteria, amidase and formamidase enzyme activities were not induced by medium supplementation with their respective substrates, acrylamide and formamide. AmiE protein expression and amidase enzyme activity were iron-repressed in H. pylori 26695 but constitutive in the isogenic fur mutant. This regulation was mediated at the transcriptional level via the binding of Fur to the amiE promoter region. In contrast, formamidase enzyme activity was not iron-repressed but was significantly higher in the fur mutant. This effect was not mediated at the transcriptional level, and Fur did not bind to the amiF promoter region. These roles of Fur in regulation of the H. pylori amidases suggest that the H. pylori Fur regulator may have acquired extra functions to compensate for the absence of other regulatory systems

The structure of a PII signaling protein from a halophilic archaeon reveals novel traits and high-salt adaptations

To obtain insights into archaeal nitrogen signaling and haloadaptation of the nitrogen/carbon/energy-signaling protein PII, we determined crystal structures of recombinantly produced GlnK2 from the extreme halophilic archaeon Haloferax mediterranei, complexed with AMP or with the PII effectors ADP or ATP, at respective resolutions of 1.49 Å, 1.45 Å, and 2.60 Å. A unique trait of these structures was a three-tongued crown protruding from the trimer body convex side, formed by an 11-residue, N-terminal, highly acidic extension that is absent from structurally studied PII proteins. This extension substantially contributed to the very low pI value, which is a haloadaptive trait of H. mediterranei GlnK2, and participated in hexamer-forming contacts in one crystal. Similar acidic N-extensions are shown here to be common among PII proteins from halophilic organisms. Additional haloadaptive traits prominently represented in H. mediterranei GlnK2 are a very high ratio of small residues to large hydrophobic aliphatic residues, and the highest ratio of polar to nonpolar exposed surface for any structurally characterized PII protein. The presence of a dense hydration layer in the region between the three T-loops might also be a haloadaptation. Other unique findings revealed by the GlnK2 structure that might have functional relevance are: the adoption by its T-loop of a three-turn α-helical conformation, perhaps related to the ability of GlnK2 to directly interact with glutamine synthetase; and the firm binding of AMP, confirmed by biochemical binding studies with ATP, ADP, and AMP, raising the possibility that AMP could be an important PII effector, at least in archaea.This work was supported by grants from the Spanish government (BFU2011-30407 and BIO2008_00082, to V. Rubio and M. J. Bonete, respectively) and from the Valencian government (Prometeo 2009/51 to V. Rubio). C. Palanca is a JAE-Predoc fellow of the CSIC and, during this work, L. Pedro-Roig was a FPU fellow of the Spanish Ministry of Education. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007–2013) under BioStruct-X (grant agreement No. 283570)

Mechanism of Disruption of the Amt-GlnK Complex by PII-Mediated Sensing of 2-Oxoglutarate

GlnK proteins regulate the active uptake of ammonium by Amt transport proteins by inserting their regulatory T-loops into the transport channels of the Amt trimer and physically blocking substrate passage. They sense the cellular nitrogen status through 2-oxoglutarate, and the energy level of the cell by binding both ATP and ADP with different affinities. The hyperthermophilic euryarchaeon Archaeoglobus fulgidus possesses three Amt proteins, each encoded in an operon with a GlnK ortholog. One of these proteins, GlnK2 was recently found to be incapable of binding 2-OG, and in order to understand the implications of this finding we conducted a detailed structural and functional analysis of a second GlnK protein from A. fulgidus, GlnK3. Contrary to Af-GlnK2 this protein was able to bind both ATP/2-OG and ADP to yield inactive and functional states, respectively. Due to the thermostable nature of the protein we could observe the exact positioning of the notoriously flexible T-loops and explain the binding behavior of GlnK proteins to their interaction partner, the Amt proteins. A thermodynamic analysis of these binding events using microcalorimetry evaluated by microstate modeling revealed significant differences in binding cooperativity compared to other characterized PII proteins, underlining the diversity and adaptability of this class of regulatory signaling proteins

Étude de la réalisation de dépôts de silico-alumineux (émaux) par projection thermique sur des substrats thermo dégradables

Un procédé d'émaillage de substrats thermosensibles par projection thermique à la flamme O2-C2H2 a été mis au point. L'optimisation de la composition et de la morphologie des poudres d'émaux s'est révélée nécessaire pour maîtriser l'architecture des dépôts. Les effets des paramètres opératoires ont été discriminés par plans d'expériences et des conditions optimisées d'élaboration ont été définies y compris pour l'élaboration de dépôts pigmentés. Ceci a permis d'adresser le mécanisme de formation des couches d'émaux singulier en regard d'autres céramiques. Des essais sur substrats de grandes surfaces (~1 m ) ont alors été réalisés pour estimer les effets de la thermique sur le mécanisme de formation des couches et limiter la dégradation du substrat. Un préchauffage du substrat s'est révélé nécessaire à une bonne adhérence du dépôt. Quelques propriétés d'usage des couches ont enfin été établies. Leurs caractéristiques mécaniques ne sont notamment pas altérées par des cycles de gel/dégel.A glazing thermal spraying process adapted to thermally sensitive substrates was developed here. An oxyacetylene flame torch was used. The optimization of glaze powders morphology (densification) and chemical composition was necessary to control coatings architectures. Effects of operating parameters were determined by a design of experiments and operating parameters were optimized. Colored coatings can have been manufactured by insert pigments addition. The coating formation mechanism was hence deduced: it differs from the one encountered for other ceramic materials. Then, glaze coatings were manufactured on larger surfaces (~1 m ) to determine the effects of thermal flux on the coating formation mechanism and to limit the substrate degradation. A substrate preheating was necessary to improve coating adhesion. At last, some coatings properties were determined. For example, coatings mechanical characteristics were not modified by freeze-thaw cycles.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Inhibition of Cell Division Suppresses Heterocyst Development in Anabaena sp. Strain PCC 7120

When the filamentous cyanobacterium Anabaena PCC 7120 is exposed to combined nitrogen starvation, 5 to 10% of the cells along each filament at semiregular intervals differentiate into heterocysts specialized in nitrogen fixation. Heterocysts are terminally differentiated cells in which the major cell division protein FtsZ is undetectable. In this report, we provide molecular evidence indicating that cell division is necessary for heterocyst development. FtsZ, which is translationally fused to the green fluorescent protein (GFP) as a reporter, is found to form a ring structure at the mid-cell position. SulA from Escherichia coli inhibits the GTPase activity of FtsZ in vitro and prevents the formation of FtsZ rings when expressed in Anabaena PCC 7120. The expression of sulA arrests cell division and suppresses heterocyst differentiation completely. The antibiotic aztreonam, which is targeted to the FtsI protein necessary for septum formation, has similar effects on both cell division and heterocyst differentiation, although in this case, the FtsZ ring is still formed. Therefore, heterocyst differentiation is coupled to cell division but independent of the formation of the FtsZ ring. Consistently, once the inhibitory pressure of cell division is removed, cell division should take place first before heterocyst differentiation resumes at a normal frequency. The arrest of cell division does not affect the accumulation of 2-oxoglutarate, which triggers heterocyst differentiation. Consistently, a nonmetabolizable analogue of 2-oxoglutarate does not rescue the failure of heterocyst differentiation when cell division is blocked. These results suggest that the control of heterocyst differentiation by cell division is independent of the 2-oxoglutarate signal