RNA binding of Hfq monomers promotes RelA-mediated hexamerization in a limiting Hfq environment

The RNA chaperone Hfq, acting as a hexamer, is a known mediator of post-transcriptional regulation, expediting basepairing between small RNAs (sRNAs) and their target mRNAs. However, the intricate details associated with Hfq-RNA biogenesis are still unclear. Previously, we reported that the stringent response regulator, RelA, is a functional partner of Hfq that facilitates Hfq-mediated sRNA–mRNA regulation in vivo and induces Hfq hexamerization in vitro. Here we show that RelA-mediated Hfq hexamerization requires an initial binding of RNA, preferably sRNA to Hfq monomers. By interacting with a Shine–Dalgarno-like sequence (GGAG) in the sRNA, RelA stabilizes the initially unstable complex of RNA bound-Hfq monomer, enabling the attachment of more Hfq subunits to form a functional hexamer. Overall, our study showing that RNA binding to Hfq monomers is at the heart of RelA-mediated Hfq hexamerization, challenges the previous concept that only Hfq hexamers can bind RNA.

RNA binding of Hfq monomers promotes RelA-mediated hexamerization in a limiting Hfq environment

The RNA chaperone Hfq acting as a hexamer, is a known mediator of post-transcriptional regulation expediting basepairing between small RNAs (sRNAs) and their target mRNAs. However, the intricate details associated with Hfq-RNA biogenesis are still unclear. Previously, we reported that the stringent response regulator, RelA is a functional partner of Hfq that facilitates Hfq-mediated sRNA-mRNA regulation in vivo and induces Hfq hexamerization in vitro. Here, for the first time we show that RelA-mediated Hfq hexamerization requires an initial binding of RNA, preferably sRNA to Hfq monomers. By interacting with a Shine-Dalgarno-like sequence (GGAG) in the sRNA, RelA stabilizes the initially unstable complex of RNA bound-Hfq monomer, enabling the attachment of more Hfq subunits to form a functional hexamer. Overall, our study showing that RNA binding to Hfq monomers is at the heart of RelA-mediated Hfq hexamerization, challenges the previous concept that only Hfq hexamers can bind RNA.

Mercury(II) reduction and sulfite oxidation in aqueous systems: kinetics study and speciation modeling

Environmental contextWastewater contains various substances such as sulfur-containing chemicals and heavy metals including mercury ions. Several technologies have been developed to trap mercury ions; however, mercury can undergo reactions with sulfite and change to its vapour form, which easily escapes to the atmosphere. Here, we devised a model to predict the formation of vapour-phase mercury as a function of sulfite concentration, temperature and water acidity based on coal-fired power plant wastewater. AbstractThe re-emission of mercury (Hg) as a consequence of the formation and dissociation of the unstable complex HgSO3 is a problem encountered in flue gas desulfurisation treatment in coal-fired power plants. A model following a pseudo-second-order rate law for Hg2+ reduction was derived as a function of [SO32–], [H+] and temperature and fitted to experimentally obtained data to generate kinetics rate values of 0.120±0.04, 0.847±0.07, 1.35±0.4mM–1 for 40°C, 60°C and 75°C respectively. The rate of reduction of Hg2+ increases with a temperature increase but shows an inverse relationship with proton concentration. Plotting the model-fit kinetics rate constants yields ΔH=61.7±1.82 kJ mol–1, which is in good agreement with literature values for the formation of Hg0 by SO32–. The model could be used to better understand the overall Hg2+ re-emission due to SO32– happening in aquatic systems such as flue gas desulfurisation wastewaters.

EDTA as a corrosion inhibitor for Al in 0.5 M HCl: adsorption, thermodynamic and theoretical study

<p class="Default"><span lang="EN-US">In this study; EDTA is used in very small amount (10^-10 M) as an inhibitor for the Al corrosion in 0.5 M HCl. Thermodynamic and adsorption parameters are calculated. The result shows that, in this range of concentrations, EDTA is chemisorbed at the Al surface, forming a stable complex with Al and give inhibition efficiency up to 89 %. For more con­centration, unstable complex is formed and acceleration of corrosion occurs. The adsorp­tion fit well to Langmuir, Temkin isotherms and El-awady model. Density functional theory (DFT) is used to study the geometrical optimizations of EDTA. From the obtained optimized structure, The highest occupied molecular orbital (EHOMO), the lowest unoc­cupied molecular orbital (ELUMO and their energy difference (ΔE), the total energy (TE), electronegativity (χ), dipole moment (µ), global hardness (η), global softness (σ), elec­tron affinity (A), ionization potential (I), the fraction of electrons transferred (∆N) and were determined using B3LYP/6-31G(d,p) basis set.</span></p>