Relation Between Conductivity and Ion Content in Urban Wastewater

Wastewater conductivity has been monitored for extended periods of time by in situ probes and on grabbed samples in four communities (from 1,000 to 350,000 PE). In parallel, the concentrations of the main ionic contributors, such as calcium, sodium, potassium, magnesium, ammonium, ortho-phosphate, chloride and sulphate have been measured and their variations with respect to time compared to human activity patterns. It appears that sodium, potassium, ammonium and ortho-phosphate, which contribute to about 34% to wastewater conductivity, exhibit diurnal variations in phase with human activity evaluated by absorbance at 254 nm. However calcium (≈ 22% of wastewater conductivity) is out‑of-phase. This release, ahead of the one of other cations and anions, could be related to sewer concrete corrosion or to groundwater infiltration. The combination of these different ionic contributions creates a conductivity pattern which cannot be easily related to human activity. It makes difficult to integrate conductivity in a monitoring system able to detect ion-related abnormalities in wastewater quality.Les variations de la conductivité d’eaux usées urbaines ont été suivies sur de longues durées a l’aide de sondes placées in situ en entrée d’installations de traitement et sur des échantillons prélevés automatiquement. Quatre communautés (entre 1 000 et 350 000 habitants) ont été choisies pour cette étude. On a également dosé sur les échantillons les principaux ions (calcium, sodium, potassium, magnésium, ammonium, ortho-phosphates, chlorures et sulfates). Il apparait que le sodium, le potassium, l’ammonium et les ortho-phosphates contribuent pour 34 % a la conductivité des eaux usées et présentent des variations journalicres en phase avec la pollution carbonée soluble, estimée a partir de l’absorbance a 254 nm. Par contre, le calcium, qui contribue pour 22 % a la conductivité, présente un déphasage qui peut ztre du a son transport dans le réseau d’assainissement du fait de la corrosion des conduites en béton ou a des infiltrations d’eaux claires. Finalement, la combinaison de ces différentes contributions ioniques conduit a une variabilité de la conductivité qu’il n’est pas facile de lier a l’activité humaine, et donc a des rejets accidentels dans le cadre d’un systcme de détection de variation anormale de la qualité des eaux usées

Structural Basis for DNA Gyrase Interaction with Coumermycin A1

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Monitoring of the retinoic acid receptor–retinoid X receptor dimerization upon DNA binding by native mass spectrometry

International audienceIdentifying protein-DNA interactions is essential to understand the regulatory networks of cells and their influence on gene expression. In this study, we use native electrospray mass spectrometry (ESI-MS) to investigate how the heterodimerization of retinoic acid receptor-retinoid X receptor (RAR-RXR) is mediated by DNA sequence. In presence of various RAR response elements (RAREs), three oligomeric states of RAR-RXR DNA binding domains (DBDs) bound to RAREs (monomer, homo- or heterodimers) were detected and individually monitored to follow subunit assembly and disassembly upon RAREs' abundancy or sequence. In particular, a cooperative heterodimerization was shown with RARb2 DR5 (5 base pair spaced direct repeat) while a high heterogeneity reflecting random complex formation could be observed with the DR0 response elements, in agreement with native gel electrophoresis data or molecular modeling. Such MS information will help to identify the composition of species formed in solution and to define which DR sequence is specific for RAR-RXR heterodimerization

Modulation of E-Cadherin Monomer Folding by Cooperative Binding of Calcium Ions

Classical cadherins are transmembrane glycoproteins involved in calcium-dependent cellcell adhesion. Calcium ions are coordinated at the interface between successive modules of the cadherin ectodomain and are thought to regulate the adhesive interactions of cadherins when present at millimolar concentrations. It is widely accepted that calcium plays a critical role in cadherin-mediated cell-cell adhesion, but the nature of cadherin-calcium binding remains a matter of debate. We investigated the parameters of noncovalent cadherin-calcium binding, using the two N-terminal modules of E-cadherin (E/EC12) with a native N-terminal end and nondenaturing electrospray ionization mass spectrometry. By directly visualizing the molecular complexes, we demonstrated that E/EC12 binds three calcium ions, with an average KD of 20 ( 0.7 íM. These calcium ions bound cooperatively to E/EC12 in its monomeric state, and these properties were not modified by an N-terminal extension consisting of a single methionine residue. This binding induced specific structural changes, as shown by assessments of protease sensitivity, circular dichroism, and mass spectrometry. Furthermore, the D103A mutation (a residue involved in E-cadherin adhesive function) modified calcium binding and led to a loss of cooperativity and the absence of structural changes, despite calcium binding. As the amino acids involved in calcium binding are found within the cadherin consensus motif, our findings may be relevant to other members of the cadherin famil

A Vitamin D Receptor Selectively Activated by Gemini Analogs Reveals Ligand Dependent and Independent Effects

The bioactive form of vitamin D [1,25(OH)2D3] regulates mineral and bone homeostasis and exerts potent anti-inflammatory and antiproliferative properties through binding to the vitamin D receptor (VDR). The 3D structures of the VDR ligand-binding domain with 1,25(OH)2D3 or gemini analogs unveiled the molecular mechanism underlying ligand recognition. On the basis of structure-function correlations, we generated a point-mutated VDR (VDRgem) that is unresponsive to 1,25(OH)2D3, but the activity of which is efficiently induced by the gemini ligands. Moreover, we show that many VDR target genes are repressed by unliganded VDRgem and that mineral ion and bone homeostasis are more impaired in VDRgem mice than in VDR null mice, demonstrating that mutations abolishing VDR ligand binding result in more severe skeletal defects than VDR null mutations. As gemini ligands induce VDRgem transcriptional activity in mice and normalize their serum calcium levels, VDRgem is a powerful tool to further unravel both liganded and unliganded VDR signaling