An ATP13A1-assisted topogenesis pathway for folding multi-spanning membrane proteins.

Many multi-spanning membrane proteins contain poorly hydrophobic transmembrane domains (pTMDs) protected from phospholipid in mature structure. Nascent pTMDs are difficult for translocon to recognize and insert. How pTMDs are discerned and packed into mature, muti-spanning configuration remains unclear. Here, we report that pTMD elicits a post-translational topogenesis pathway for its recognition and integration. Using six-spanning protein adenosine triphosphate-binding cassette transporter G2 (ABCG2) and cultured human cells as models, we show that ABCG2's pTMD2 can pass through translocon into the endoplasmic reticulum (ER) lumen, yielding an intermediate with inserted yet mis-oriented downstream TMDs. After translation, the intermediate recruits P5A-ATPase ATP13A1, which facilitates TMD re-orientation, allowing further folding and the integration of the remaining lumen-exposed pTMD2. Depleting ATP13A1 or disrupting pTMD-characteristic residues arrests intermediates with mis-oriented and exposed TMDs. Our results explain how a "difficult" pTMD is co-translationally skipped for insertion and post-translationally buried into the final correct structure at the late folding stage to avoid excessive lipid exposure.

Limestone water mixing process and hydrogen and oxygen stable isotope fractionation response under mining action.

North China type coalfield are gradually mining deep, and the mixing of groundwater is intensified. Hydrogen and oxygen isotopes are important elements for tracing groundwater movement. The fractionation response mechanism under mining conditions is not clear. In this paper, combined with numerical simulation, MixSIAR isotope mixing model and other methods, according to the δD, δ18O and hydrochemical information of various water bodies, the impact of coal mining on hydrogen and oxygen isotope fractionation is analyzed from multiple perspectives. The results show that summer soil water is the main source of recharge for limestone water, accounting for 30.7%-41.5%, and the Zhan River is the main source of recharge for limestone water. Before groundwater recharge, evaporation leads to the increase of δ18O in surface water by 0.31‰-5.58‰, water loss by 1.81%-28.00%, the increase of δ18O in soil water by 0.47‰-6.33‰, and water loss by 2.74%-35.80%. Compared with the coal mining layer, the degree of hydrogen and oxygen isotope drift and water-rock interaction in the coal mine stopping layer are significantly improved. The results of numerical simulation show that the pumping activity reduces the 18O concentration in the mining layer. The ion ratio is used as a new variable to eliminate the influence of water-rock interaction when calculating the mixing ratio. The results show that the limestone water is in a state of receiving external recharge, and mixing effect increases the δ18O in limestone water by 0.86‰ on average, and the δD increases by 0.72‰ on average. The research results explain the controlled process of hydrogen and oxygen isotope fractionation under mining conditions, which is of great significance to coal mine safety production.

A multiple isotope (S, H, O and C) approach to estimate sulfate increasing mechanism of groundwater in coal mine area.

Groundwater in North China type coal mine area is an important source of domestic, industrial and agricultural water. To explore the sulfate increasing mechanism of groundwater in mining area and identify key influencing factors. In this paper, hydrochemistry and multi-isotope tracer techniques such as δ34SSO4, δ18OSO4, δ2HH2O, δ18OH2O and δ13CDIC were used to study the groundwater circulation law and the migration and transformation mechanism of sulfate and carbonate in coal mine area. The results show that: the hydrochemical types of groundwater in the coal mine area are mainly HCO3- and SO42- anions, while the cations are mainly Ca2+ and Mg2+. The sulfate content is significantly increased, and the pH shows weak alkalinity; the relationship between δ18OH2O and δ18HH2O shows that the dynamic field of groundwater changes significantly after coal mining or closure, and limestone water mainly comes from surface water recharge through 'skylight' infiltration. The relationships between δ18OSO4 and δ18OH2O, δ34SSO4 and δ18OSO4 show that the sulfate in groundwater of coal mine area is mainly derived from sulfide oxidation. The ∆δ18OSO4-H2O value of groundwater in coal mine area is greater than 8 ‰, and the oxygen content in sulfate is 25 %-75 % from oxygen in water, indicating that coal mining has disturbed the groundwater in the study area from reducing environment to oxidizing environment, promoted sulfide oxidation, and accelerated the dissolution of carbonate minerals. The δ13CDIC value and δ34SSO4 value in the coal mine area are inversely proportional. The δ13CDIC of groundwater in the coal mine area is affected by the δ34SSO4 value to a certain extent. Sulfuric acid participates in the dissolution of carbonate minerals, making the pH value weak and alkaline as a whole. This paper expounds the migration and transformation law of sulfate in groundwater in coal mine area, which has practical significance for groundwater quality management. The research results can provide theoretical support for the rational development and utilization of groundwater resources in coal mine areas.

UBE4A catalyzes NRF1 ubiquitination and facilitates DDI2-mediated NRF1 cleavage.

The transcription factor nuclear factor erythroid 2 like 1 (NFE2L1 or NRF1) regulates constitutive and inducible expression of proteasome subunits and assembly chaperones. The precursor of NRF1 is integrated into the endoplasmic reticulum (ER) and can be retrotranslocated from the ER to the cytosol where it is processed by ubiquitin-directed endoprotease DDI2. DDI2 cleaves and activates NRF1 only when NRF1 is highly polyubiquitinated. It remains unclear how retrotranslocated NRF1 is primed with large amount of ubiquitin and/or very long polyubiquitin chain for subsequent processing. Here, we report that E3 ligase UBE4A catalyzes ubiquitination of retrotranslocated NRF1 and promotes its cleavage. Depletion of UBE4A reduces the amount of ubiquitin modified on NRF1, shortens the average length of polyubiquitin chain, decreases NRF1 cleavage efficiency and causes accumulation of non-cleaved, inactivated NRF1. Expression of a UBE4A mutant lacking ligase activity impairs the cleavage, likely due to a dominant negative effect. UBE4A interacts with NRF1 and the recombinant UBE4A can promote ubiquitination of retrotranslocated NRF1 in vitro. In addition, knocking out UBE4A reduces transcription of proteasomal subunits in cells. Our results indicate that UBE4A primes NRF1 for DDI2-mediated activation to facilitate expression of proteasomal genes.

Identification of mixing water source and response mechanism of radium and radon under mining in limestone of coal seam floor.

With the gradual increase of the coal mining depth, the mixing of multiple water sources intensifies and the activity of radium and radon in groundwater increases. Identifying the source of mine water inrush by using radium and radon isotopes is a new choice. In this paper, the mathematical statistics method, radioactive isotope decay theory, the mass conservation principle, and the numerical simulation method are used to analyze the influence of total dissolved solids (TDS), pH, and the hydrochemical ion content in groundwater on the isotope activity of radium, radon, uranium, thorium, and lead. The activity of thorium and lead is lower than the detection limit of the instrument, and the influence of coal mining activities on it is small. The simulation of the radium-radon mass balance in groundwater shows that the greater the adsorption coefficient (k) of solid particles in groundwater is, the more obvious the adsorption effect and the greater the influence on the radium-radon activity balance are. The radium-radon dating method is used to calculate the groundwater age. Results show that the groundwater age in the closed pit coal mining area is generally older than that in the mining coal mining area. Combined with the 222Rn, 226Ra, and 234U radioactive isotopes and temperature, a mixing water source identification model of limestone in the coal seam floor is constructed. The model shows that the radium activity and temperature of the groundwater are inversely proportional to the mixing ratio of the Permian sandstone water. From the closed pit coal mining area to the mining coal mining area, the radium radon activity of the groundwater increases gradually, the groundwater age decreases significantly, the water cycle is accelerated, the mixing ratio of the Permian sandstone water decreases gradually, the mixing ratio of the Ordovician limestone water increases gradually, and the risk of coal mine water inrush increases. The research results prove the feasibility of the new method for accurately discriminating the mixing water sources in coal mine areas, which is of great significance to the improvement of the theory of coal mine water disaster prevention and control.

Trace metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls in the surface sediments from Sanya River, China: Distribution, sources and ecological risk.

The urban inland river ecosystems are now facing comprehensive pollution and governance pressures. Up to now, few works related to the multiple pollution assessment of trace metals, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) for the urban inland river sediments have been reported in China. Our study investigated the spatial distribution, ecological risk and potential sources of trace metals, PAHs and PCBs in surface sediment collected from 20 sampling sites of Sanya River, Hainan Province, China. The pollution status and potential ecological risk of trace metals were evaluated using the contamination indexes including geoaccumulation index (Igeo), individual potential ecological risk (Eri), potential ecological risk index (RI) and pollution load index (PLI). Considering the carcinogenicity and toxicity of PAHs and PCBs to human health and the ecological environment, we also analyzed the distributions, sources and adverse biological effects of PAHs and PCBs according to the sediment quality guidelines (SQGs), principal component analysis (PCA) and other source analysis. This study revealed that the surface sediments in Sanya River were extremely slight pollution and showed a very low ecological risk according to Igeo, Eri, PLI and RI results for trace metals. Besides, PAHs and PCBs pollution detected may not pose considerable adverse biological effect to ecological environment in a foreseeable period on the basis of comprehensive research results. The overall surface sediments quality of the Sanya River not seem to pose a serious pollution and ecological risk based on the evaluation results of multiple pollution factors. The study provided detailed information on the multiple pollution status and location of surface sediments, one of the key environmental indicators of international tourism cities, in the Sanya River, which would be useful for the water quality improvement of Sanya River and the environmental remediation of the other coastal ecosystems from different regions.

Design of facile technology for the efficient removal of hydroxypropyl guar gum from fracturing fluid.

With the increasing demand for energy, fracturing technology is widely used in oilfield operations over the last decades. Typically, fracturing fluids contain various additives such as cross linkers, thickeners and proppants, and so forth, which makes it possess the properties of considerably complicated components and difficult processing procedure. There are still some difficult points needing to be explored and resolved in the hydroxypropyl guar gum (HPG) removal process, e.g., high viscosity and removal of macromolecular organic compounds. Our works provided a facile and economical HPG removal technology for fracturing fluids by designing a series of processes including gel-breaking, coagulation and precipitation according to the diffusion double layer theory. After this treatment process, the fracturing fluid can meet the requirements of reinjection, and the whole process was environment friendly without secondary pollution characteristics. In this work, the fracturing fluid were characterized by scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy technologies, etc. Further, the micro-stabilization and destabilization mechanisms of HPG in fracturing fluid were carefully investigated. This study maybe opens up new perspective for HPG removal technologies, exhibiting a low cost and strong applicability in both fundamental research and practical applications.

Biochar/iron (BC/Fe) composites for soil and groundwater remediation: Synthesis, applications, and mechanisms.

Biochar/iron (BC/Fe) composites, such as nano zero-valent iron (nZVI)/BC, iron sulfide/BC, and iron oxide/BC, have been developed and applied to deal with various contaminants owing to their excellent physicochemical properties. This work summarizes the progress in the preparation of BC/Fe composites, the properties and applications of BC/Fe, and the mechanism of the synergistic effect between Fe and BC in the composites. Various methods, including pyrolysis, hydrothermal carbonization, fractional precipitation, and ball milling, have been used to synthesize BC/Fe composites. In addition, the introduction of stabilizers, such as carboxymethyl cellulose (CMC), in the fractional precipitation process further prevents the agglomeration of Fe particles, which enhances the stability and fluidity of the resultant composites to facilitate the application of the composites in soil and water remediation. The application of BC/Fe composites in water and soil remediation is discussed in three aspects based on the interaction mechanisms, namely adsorption, reduction, and oxidation. Overall, the composites showed the synergistic effect of BC and Fe owing to the combination of the specific properties of Fe, such as reduction, catalysis, and magnetism, which can enhance the properties of BC with a larger surface area, abundant functional groups, and increased electron transfer efficiency. This review systemically summarizes the recent developments in BC/Fe composites to maximize the efficiency of BC/Fe application in soil and groundwater remediation. Key challenges and further research needs are also suggested.

Waste cigarette filter as nanofibrous membranes for on-demand immiscible oil/water mixtures and emulsions separation.

The rapid industrial growth and the frequent oil spill accidents have led to the large production of oily wastewater. Thus, it is urging to develop a low-cost and eco-friendly material to purify the oily wastewater. In our work, the waste cigarette filter as the raw material was used to prepare cigarette filter coated meshes (CFCMs) by a facile electrospinning approach. The as-prepared CFCMs prewetted with water or oil achieved the special wetting performance of underwater superoleophobicity or underoil superhydrophobicity without any further chemical modification. Hence, the cigarette filter coated meshes with larger or smaller pore size can be applied to on-demand immiscible oil/water mixtures (light or heavy oil/water mixtures) and oil/water emulsions separation (water-in-oil or oil-in-water emulsions), respectively. Moreover, the CFCMs still exhibited high separation efficiency larger than 99.9% for immiscible oil/water mixtures and emulsions after many cyclic testing. The work provides an application in oil/water separation for waste cigarette filters and contributes to reduce the pollution for environment from the waste cigarette filters.

Negative impact of the imidazolium-based ionic liquid [C8mim]Br on silver carp (Hypophthalmichthys molitrix): Long-term and low-level exposure.

This study aimed to determine the chronic toxicity of the ionic liquid (IL) 1-methyl-3-octylimidazolium bromide ([C8mim]Br) on silver carp to further study the toxicological mechanism of ILs. For this purpose, 60-d chronic exposure at concentrations of 1.09 or 4.38 mg L-1 [C8mim]Br in silver carp was conducted. The results of biochemical assays revealed that [C8mim]Br-treatment remarkably promoted serum lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, indicating that [C8mim]Br-exposure caused fish organ damage. Long-term exposure of [C8mim]Br also altered the activities of superoxide dismutase (SOD) and catalase (CAT) and the glutathione (GSH) level but increased malondialdehyde (MDA) levels in fish brain, gill, intestine, kidney, liver, and muscle, suggesting that [C8mim]Br-treatment may cause oxidative stress in fish organs. Further work revealed that [C8mim]Br-treatment increased the activities of erythromycin-N-demethylase (ERND) and glutathione S-transferases (GST), which may participate in the metabolism of [C8mim]Br in fish liver. Moreover, chronic [C8mim]Br-exposure remarkably promoted the expression of inducible nitric oxide synthase (iNOS), interleukin-1ß (IL-1ß), tumour necrosis factor-α (TNF-α), and nuclear factor-κB (NF-κB) and altered the levels of transforming growth factor-ß (TGF-ß), suggesting that long-term exposure of [C8mim]Br might promote the inflammatory response in fish liver. Additionally, [C8mim]Br-exposure altered succinate dehydrogenase (SDH) activity and promoted caspase-9 and caspase-3 activities in fish liver, suggesting that chronic [C8mim]Br-exposure also induces hepatocellular apoptosis via the mitochondrial pathway. The results presented here may be helpful to illuminate the chronic toxicity mechanism of imidazolium-based ILs and safe use of ILs in the future.