Aluminum tolerance in Pseudomonas fluorescens ATCC 13525: Involvement of a gelatinous lipid-rich residue

Abstract Pseudomonas fluorescens was found to grow in a mineral medium supplemented with up to 50 mM aluminum, complexed to citrate, the sole source of carbon. At stationary phase while virtually no diminution in cellular yield was observed in the presence of 1.0 mM aluminum, only 31% of bacterial yield was recorded in media with 50 mM aluminum. The decrease in soluble aluminum in the culture fluid was concomitant with the formation of a gelatinous residue. At later stages of growth, the trivalent metal was immobilized in this deposit. This bioprecipitate consisted of lipid moieties but was apparently devoid of proteins and carbohydrates. X-ray fluorescence spectroscopy and colorimetric assays also revealed the presence of aluminum and phosphorus. X-ray diffraction spectroscopy indicated that the biomineral was amorphous. Examination of the gelatinous residue by scanning electron microscopy and energy dispersive X-ray microanalysis aided in the identification of aluminum, oxygen and phosphorus rich irregular bodies that were associated with carbon containing thread-like structures.     

Differential Involvement of the Dentate Gyrus in Adaptive Forgetting in the Rat

How does the brain discriminate essential information aimed to be stored permanently from information required only temporarily, and that needs to be cleared away for not saturating our precious memory space? Reference Memory (RM) refers to the long-term storage of invariable information whereas Working Memory (WM) depends on the short-term storage of trial-unique information. Previous work has revealed that WM tasks are very sensitive to proactive interference. In order to prevent such interference, irrelevant old memories must be forgotten to give new ones the opportunity to be stabilized. However, unlike memory, physiological processes underlying this adaptive form of forgetting are still poorly understood. Here, we precisely ask what specific brain structure(s) could be responsible for such process to occur. To answer this question, we trained rats in a radial maze using three paradigms, a RM task and two WM tasks involving or not the processing of interference but strictly identical in terms of locomotion or motivation. We showed that an inhibition of the expression of Zif268 and c-Fos, two indirect markers of neuronal activity and synaptic plasticity, was observed in the dentate gyrus of the dorsal hippocampus when processing such interfering previously stored information. Conversely, we showed that inactivating the dentate gyrus impairs both RM and WM, but improves the processing of interference. Altogether, these results strongly suggest for the first time that the dentate gyrus could be a key structure involved in adaptive forgetting.     

Learning chemistry with multiple first-principles simulations

Huge parallel high-performance computing (HPC) architectures are today available laboratories for modelling atomic forces with high accuracy and for large samples of atoms. Modern statistical tools allow to simulate the statistics of these samples, while first-principles molecular dynamics (MD) can probe the interactions within large atomic samples, including possible chemical reactions. But a proper statistical convergence for the ensemble, represented in terms of a bundle of trajectories, is still unsatisfactory in terms of comparisons with experiments. Can we learn something by these HPC experiments? In this contribution, we show one example, where the occurrence of a chemical reaction in a disordered system is probed. The complex of the copper ion and a segment of the amyloid-β peptide, of wide interest in understanding the progress of Alzheimer's disease, was modelled combining constructions based on empirical force fields with first-principles MD simulations. We simulate a bundle of 16 different structures, biasing different Cu coordination numbers and changing the charge (oxidation state) of the assembly. Even within the given approximations for forces and the poor sampling, we could identify the structures of the complex that are able to react with hydrogen peroxide. The observation explains, at a molecular level, one important linkage between Alzheimer's disease and oxidative stress. This is an example of a general strategy for exploiting reactive configurations within a large set of possible reasonable candidates.     

Insights into substrate gating in H. influenzae rhomboid

Rhomboids are a remarkable class of serine proteases that are embedded in lipid membranes. These membrane-bound enzymes play key roles in cellular signaling events, and disruptions in these events can result in numerous disease pathologies, including hereditary blindness, type 2 diabetes, Parkinson's disease, and epithelial cancers. Recent crystal structures of rhomboids from Escherichia coli have focused on how membrane-bound substrates gain access to a buried active site. In E. coli, it has been shown that movements of loop 5, with smaller movements in helix 5 and loop 4, act as substrate gate, facilitating inhibitor access to rhomboid catalytic residues. Herein we present a new structure of the Haemophilus influenzae rhomboid hiGlpG, which reveals disorder in loop 5, helix 5, and loop 4, indicating that, together, they represent mobile elements of the substrate gate. Substrate cleavage assays by hiGlpG with amino acid substitutions in these mobile regions demonstrate that the flexibilities of both loop 5 and helix 5 are important for access of the substrates to the catalytic residues. Mutagenesis indicates that less mobility by loop 4 is required for substrate cleavage. A reexamination of the reaction mechanism of rhomboid substrates, whereby cleavage of the scissile bond occurs on the si-face of the peptide bond, is discussed.     

Overexpression of active Aurora-C kinase results in cell transformation and tumour formation

Aurora kinases belong to a conserved family of serine/threonine kinases key regulators of cell cycle progression. Aurora-A and Aurora-B are expressed in somatic cells and involved mainly in mitosis while Aurora-C is expressed during spermatogenesis and oogenesis and is involved in meiosis. Aurora-C is hardly detectable in normal somatic cells. However all three kinases are overexpressed in many cancer lines. Aurora-A possesses an oncogenic activity while Aurora-B does not. Here we investigated whether Aurora-C possesses such an oncogenic activity. We report that overexpression of Aurora-C induces abnormal cell division resulting in centrosome amplification and multinucleation in both transiently transfected cells and in stable cell lines. Only stable NIH3T3 cell clones overexpressing active Aurora-C formed foci of colonies when grown on soft agar, indicating that a gain of Aurora-C activity is sufficient to transform cells. Furthermore, we reported that NIH-3T3 stable cell lines overexpressing Aurora-C induced tumour formation when injected into nude mice, demonstrating the oncogenic activity of enzymatically active Aurora kinase C. Interestingly enough tumor aggressiveness was positively correlated with the quantity of active kinase, making Aurora-C a potential anti-cancer therapeutic target.