Unusual relatives of the multisubunit RNA polymerase

Transcription, the first step of gene expression, is accomplished in all domains of life by the multisubunit RNA polymerase (msRNAP). Accordingly, the msRNAP is an ancient enzyme that is ubiquitous across all cellular organisms. Conserved in absolutely all msRNAPs is the catalytic magnesium-binding aspartate triad and the structural fold it is present on, the double ψ β barrel (DPBB). In-depth bioinformatics has begun to reveal a wealth of unusual proteins distantly related to msRNAP, identified due to their possession of the aspartate triad and DPBB folds. Three examples of these novel RNAPs are YonO of the Bacillus subtilis SPβ prophage, non-virion RNAP (nvRNAP) of the B. subtilis AR9 bacteriophage and ORF6 RNAP of the Kluyveromyces lactis cytoplasmic killer system. While YonO and AR9 nvRNAP are both bacteriophage enzymes, they drastically contrast. YonO is an incredibly minimal single-subunit RNAP, while AR9 nvRNAP is multisubunit bearing much more resemblance to the canonical msRNAP. ORF6 RNAP is an intermediate, given it is a single-subunit enzyme with substantial conservation with the msRNAP. Recent findings have begun to shed light on these polymerases, which have the potential to update our understanding of the mechanisms used for transcription and give new insights into the canonical msRNAP and its evolution. This mini-review serves to introduce and outline our current understanding of these three examples of novel, unusual RNAPs.

Atomic view into Plasmodium actin polymerization, ATP hydrolysis, and phosphate release

Plasmodium actins form very short filaments and have a non-canonical link between ATP hydrolysis and polymerization. Long filaments are detrimental to the parasites, but the structural factors constraining Plasmodium microfilament lengths are currently unknown. Using high-resolution crystallography, we show that magnesium binding activates the Plasmodium actin I monomer before polymerization by a slight flattening, which is reversed upon phosphate release. A coordinated potassium ion resides in the active site during hydrolysis and leaves together with the phosphate, a process governed by the position of the Arg178/Asp180-containing A-loop. Asp180 interacts with either Lys270 or His74, depending on protonation, while Arg178 links the inner and outer domains. Hence, the A-loop is a switch between stable and non-stable filament conformations. Our data provide a comprehensive model for polymerization, phosphate release, and the inherent instability of parasite microfilaments.

Magnesium binding by terrestrial humic acids

Environmental contextThe behaviour of magnesium, which is an essential element for all living organisms, in terrestrial environments is influenced by natural organic matter. This study shows that magnesium binding by terrestrial humic acids exhibits a pronounced ionic strength-dependence indicating a strong preference for electrostatic binding to humic acids. This interaction is expected to influence the mobility of humic substances and their associated trace elements. AbstractMagnesium binding by three terrestrial humic acids was investigated at pH 8 and 25 °C as a function of Mg2+ activity and ionic strength using NaCl as the background electrolyte. The Mg2+ activity in solution was directly measured with an Mg2+-selective electrode in the titration experiments. In addition, coagulation experiments using Ca2+ and Mg2+ as the coagulants were carried out at pH 8. For the titration data, the NICA–Donnan model was used to quantitatively describe Mg2+ binding to the humic acids considering electrostatic and specific Mg2+ binding. Mg2+ binding to humic acids was found to be strongly affected by ionic strength variations indicating that Mg2+ binding largely arose from electrostatic (nonspecific) interactions with negatively charged functional groups of the humic acids. Data modelling suggested that the relative contribution of specific binding increased with decreasing Mg2+ activity and was related to functional groups with low proton affinities. For all three humic acids studied, the fitted Mg2+ affinity constants for specific binding were lower than the respective Ca2+ affinities. Corresponding to the observed differences in cation binding and the known differences in ion hydration, Ca2+ was observed to be the stronger coagulant as compared with Mg2+. The results suggest that Mg2+ may influence the mobility of trace elements that are strongly bound to humic acids such as mercury, although Mg2+ is not expected to directly compete with strongly sorbing elements for specific binding.

Effect of additives on hydration and hardening of magnesia compositions

The article is devoted to the investigation of the influence of technological factors on the hydration and hardening of magnesia compositions. The objective – is investigation magnesia compositions with different additives. Factors which impact activity of magnesium oxide in compositions of different structure are investigated. Influence of liquid density on hardening of magnesium bindings is defined. Processes of hydration and hardening of magnesium bindings with participation of minerals – silicates are investigated. It is revealed that the addition of semi-aquatic calcium sulfate contributes to the hardening of magnesia binders. Defined effect of concentration calcium sulfate hemihydrate to the hardening of caustic magnesite. Here are proposed structures of sulphomagnesium compositions containing technogenic components. It revealed a beneficial effect on the hardening of ferrous component of the mixed magnesia binder. Composition of hydration products of magnesium binding with participation of ferriferous minerals is presented. Transformations of phases at hydration of magnesium binding are revealed. Influence of structure of bindings on transformations of hydrates is established. Results of research of magnesia bindings of long hardening are given. It is shown that the durability of stone of bindings is provided with dense structure of hydrates. In researches are used X – Ray and thermal methods, electronic microscopy.