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1.
J Environ Manage ; 271: 111043, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32778321

RESUMO

A neutral M2+-rich and M3+-poor (M = metal) metallurgical waste drainage was used to test a metal removal method based on the precipitation of layered double hydroxide (LDH). The LDH precipitation was induced by adding a salt of Al3+ (trivalent metal missing in the drainage) and maintaining or restoring the pH to a circum-neutral value. The precipitates were characterized by chemical analysis, XRD, ESEM, HRTEM and XAS. The main parameter controlling the removal of metals and the type of precipitate appeared to be the pH. As a function of pH variation during the experiments, analyses of precipitates and solutions showed either the formation of poor crystalline LDH combined with very high removal of Zn, Ni and Pb (92-100%), more variable removal of Mn (46-98%) and less Cd (33-40%), or the formation of more crystalline LDH combined with lower removal of Zn (62%), Mn (43%), Ni (88%), Pb (64%) and especially Cd (1%). The different metal removal efficiency in the two cases is only indirectly due to the different LDH crystallinity, and it is clearly affected by the following factors: 1) the two pH steps of the method; 2) the direction of pH variation within each step. In particular, the highest removal of metals is obtained when the first pH step goes towards acidic conditions, as a consequence of Al salt addition, and precipitation of a quasi-amorphous hydrated hydroxysulfate of Al (probably a precursor of felsÓ§bányaite Al4(SO4)(OH)10 · 4H2O) occurs. This first acidic pH step removes little or no metals (just 0-3%) but it is essential so that the second pH step towards slightly alkaline conditions, as a consequence of NaOH addition, can be highly efficient in removing divalent metals as the quasi-amorphous hydrated hydroxysulfate of Al gradually turns into an LDH incorporating Zn, Mg and other metals. On the contrary, when both pH steps remain in the neutral-alkaline range, only LDH precipitation occurs and a lower metal removal is observed. These results encourage further investigations on the removal of metals by inducing LDH precipitation as a simple and effective method for the treatment of circum-neutral polluted drainages.


Assuntos
Metais Pesados/análise , Mineração , Cátions Bivalentes , Concentração de Íons de Hidrogênio , Hidróxidos , Metalurgia
2.
Nucleic Acids Res ; 48(15): 8663-8674, 2020 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-32663277

RESUMO

Divalent metal cations are essential to the structure and function of the ribosome. Previous characterizations of the ribosome performed under standard laboratory conditions have implicated Mg2+ as a primary mediator of ribosomal structure and function. Possible contributions of Fe2+ as a ribosomal cofactor have been largely overlooked, despite the ribosome's early evolution in a high Fe2+ environment, and the continued use of Fe2+ by obligate anaerobes inhabiting high Fe2+ niches. Here, we show that (i) Fe2+ cleaves RNA by in-line cleavage, a non-oxidative mechanism that has not previously been shown experimentally for this metal, (ii) the first-order in-line rate constant with respect to divalent cations is >200 times greater with Fe2+ than with Mg2+, (iii) functional ribosomes are associated with Fe2+ after purification from cells grown under low O2 and high Fe2+ and (iv) a small fraction of Fe2+ that is associated with the ribosome is not exchangeable with surrounding divalent cations, presumably because those ions are tightly coordinated by rRNA and deeply buried in the ribosome. In total, these results expand the ancient role of iron in biochemistry and highlight a possible new mechanism of iron toxicity.


Assuntos
Cátions Bivalentes/metabolismo , Ferro/metabolismo , Clivagem do RNA/genética , Ribossomos/genética , Sítios de Ligação , Cátions Bivalentes/química , Ferro/química , Magnésio/química , Magnésio/metabolismo , Metais/química , Metais/metabolismo , Oxirredução/efeitos dos fármacos , Ribossomos/química
3.
Chemosphere ; 260: 127623, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32668363

RESUMO

The global demand of lithium is rising steadily, and many industrially advanced countries may find it hard to secure an uninterrupted supply of lithium for meeting their manufacturing demands. Thus, innovative processes for lithium recovery from a wide range of natural reserves should be explored for meeting the future demands. In this study, a novel integrated approach was investigated by combining nanofiltration (NF), membrane distillation (MD) and precipitation processes for lithium recovery from salt-lake brines. Initially, the brine was filtered with an NF membrane for the separation of lithium ions (Li+) from competing ions such as Na+, K+, Ca2+ and Mg2+. The extent of permeation of metal ions by the NF membrane was governed by their hydrated ionic radii. Rejection by NF membrane was 42% for Li, 48% for Na and 61% for K, while both the divalent cations were effectively rejected (above 90%). Importantly, in the NF-permeate, Mg2+/Li+ mass ratio reduced to less than 6 (suggested for lithium recovery). The result showed that MD can enrich lithium with a concentration of 2.5 for raw brine and 5 for NF-treated brine. Following the enrichment of NF-permeate by the MD membrane, a two-stage precipitation method was used for the recovery of lithium. X-ray diffraction confirmed the precipitation of lithium as well as the formation of lithium carbonate crystals.


Assuntos
Lagos/química , Lítio/análise , Poluentes Químicos da Água/análise , Cátions Bivalentes , Destilação , Íons , Lítio/química , Sais , Sódio , Cloreto de Sódio , Poluentes Químicos da Água/química
4.
Nucleic Acids Res ; 48(13): 7018-7026, 2020 07 27.
Artigo em Inglês | MEDLINE | ID: mdl-32542319

RESUMO

Probing the role of surface structure in electrostatic interactions, we report the first observation of sequence-dependent dsDNA condensation by divalent alkaline earth metal cations. Disparate behaviors were found between two repeating sequences with 100% AT content, a poly(A)-poly(T) duplex (AA-TT) and a poly(AT)-poly(TA) duplex (AT-TA). While AT-TA exhibits non-distinguishable behaviors from random-sequence genomic DNA, AA-TT condenses in all alkaline earth metal ions. We characterized these interactions experimentally and investigated the underlying principles using computer simulations. Both experiments and simulations demonstrate that AA-TT condensation is driven by non-specific ion-DNA interactions. Detailed analyses reveal sequence-enhanced major groove binding (SEGB) of point-charged alkali ions as the major difference between AA-TT and AT-TA, which originates from the continuous and close stacking of nucleobase partial charges. These SEGB cations elicit attraction via spatial juxtaposition with the phosphate backbone of neighboring helices, resulting in an azimuthal angular shift between apposing helices. Our study thus presents a distinct mechanism in which, sequence-directed surface motifs act with cations non-specifically to enact sequence-dependent behaviors. This physical insight allows a renewed understanding of the role of repeating sequences in genome organization and regulation and offers a facile approach for DNA technology to control the assembly process of nanostructures.


Assuntos
Cátions Bivalentes/química , DNA/química , Conformação de Ácido Nucleico , Animais , Fenômenos Biofísicos , Simulação de Dinâmica Molecular , Salmão , Eletricidade Estática
5.
Proc Natl Acad Sci U S A ; 117(25): 14512-14521, 2020 06 23.
Artigo em Inglês | MEDLINE | ID: mdl-32513714

RESUMO

Large-conductance Ca2+ and voltage-activated K+ (BK) channels control membrane excitability in many cell types. BK channels are tetrameric. Each subunit is composed of a voltage sensor domain (VSD), a central pore-gate domain, and a large cytoplasmic domain (CTD) that contains the Ca2+ sensors. While it is known that BK channels are activated by voltage and Ca2+, and that voltage and Ca2+ activations interact, less is known about the mechanisms involved. We explore here these mechanisms by examining the gating contribution of an interface formed between the VSDs and the αB helices located at the top of the CTDs. Proline mutations in the αB helix greatly decreased voltage activation while having negligible effects on gating currents. Analysis with the Horrigan, Cui, and Aldrich model indicated a decreased coupling between voltage sensors and pore gate. Proline mutations decreased Ca2+ activation for both Ca2+ bowl and RCK1 Ca2+ sites, suggesting that both high-affinity Ca2+ sites transduce their effect, at least in part, through the αB helix. Mg2+ activation also decreased. The crystal structure of the CTD with proline mutation L390P showed a flattening of the first helical turn in the αB helix compared to wild type, without other notable differences in the CTD, indicating that structural changes from the mutation were confined to the αB helix. These findings indicate that an intact αB helix/VSD interface is required for effective coupling of Ca2+ binding and voltage depolarization to pore opening and that shared Ca2+ and voltage transduction pathways involving the αB helix may be involved.


Assuntos
Cálcio/metabolismo , Ativação do Canal Iônico/genética , Subunidades alfa do Canal de Potássio Ativado por Cálcio de Condutância Alta/metabolismo , Domínios Proteicos/genética , Regulação Alostérica , Animais , Cátions Bivalentes/metabolismo , Membrana Celular/metabolismo , Cristalografia por Raios X , Subunidades alfa do Canal de Potássio Ativado por Cálcio de Condutância Alta/genética , Subunidades alfa do Canal de Potássio Ativado por Cálcio de Condutância Alta/ultraestrutura , Potenciais da Membrana , Mutagênese Sítio-Dirigida , Oócitos , Técnicas de Patch-Clamp , Prolina/genética , Conformação Proteica em alfa-Hélice/genética , Relação Estrutura-Atividade , Xenopus laevis
6.
PLoS Genet ; 16(6): e1008873, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32584819

RESUMO

The regulation of leaf size has been studied for decades. Enhancement of post-mitotic cell expansion triggered by impaired cell proliferation in Arabidopsis is an important process for leaf size regulation, and is known as compensation. This suggests a key interaction between cell proliferation and cell expansion during leaf development. Several studies have highlighted the impact of this integration mechanism on leaf size determination; however, the molecular basis of compensation remains largely unknown. Previously, we identified extra-small sisters (xs) mutants which can suppress compensated cell enlargement (CCE) via a specific defect in cell expansion within the compensation-exhibiting mutant, angustifolia3 (an3). Here we revealed that one of the xs mutants, namely xs2, can suppress CCE not only in an3 but also in other compensation-exhibiting mutants erecta (er) and fugu2. Molecular cloning of XS2 identified a deleterious mutation in CATION CALCIUM EXCHANGER 4 (CCX4). Phytohormone measurement and expression analysis revealed that xs2 shows hyper activation of the salicylic acid (SA) response pathway, where activation of SA response can suppress CCE in compensation mutants. All together, these results highlight the regulatory connection which coordinates compensation and SA response.


Assuntos
Antiporters/genética , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Reguladores de Crescimento de Planta/metabolismo , Folhas de Planta/crescimento & desenvolvimento , Ácido Salicílico/metabolismo , Proteínas de Arabidopsis/genética , Cálcio/metabolismo , Cátions Bivalentes/metabolismo , Crescimento Celular , Proliferação de Células/genética , Regulação da Expressão Gênica de Plantas , Mutação com Perda de Função , Tamanho do Órgão/genética , Folhas de Planta/citologia , Folhas de Planta/metabolismo , Plantas Geneticamente Modificadas , Transdução de Sinais/genética
7.
Food Chem ; 330: 127212, 2020 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-32526650

RESUMO

In this work, a facile solid phase extraction (SPE) method was developed for the analysis of trace Pb2+ and Cd2+ by using chitosan/thiol modified metal-organic frameworks (CS/MOF-SH) composite as adsorbent followed by graphite furnace atomic absorption spectrometer (GF-AAS) detection. The potential influencing factors, such as solution pH, adsorbent dosage, and extraction time, were fully estimated. Under the optimized extraction conditions, the detection limits of Pb2+ and Cd2+ were 0.033 µg L-1 and 0.008 µg L-1, respectively. Compared to other studies, CS/MOF-SH not only possessed superior adsorption performance, but also had the advantages of ease of handling and recyclability. Encouragingly, the developed method was of high accuracy and could monitor trace Pb2+ and Cd2+ in various certified reference materials (rice, wheat and tea) with complicated matrices, demonstrating its practical potential for regular monitoring of trace heavy metal ions in real food samples.


Assuntos
Cádmio/análise , Quitosana/química , Chumbo/análise , Estruturas Metalorgânicas/química , Compostos de Sulfidrila/química , Cádmio/química , Cátions Bivalentes , Análise de Alimentos , Chumbo/química , Oryza/química , Extração em Fase Sólida/métodos , Chá/química , Triticum/química
8.
Food Chem ; 327: 127080, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32454274

RESUMO

A hydrazone based Schiff base (SB) has been synthesized and investigated for the detection, quantification and degradation of selective organophosphates (i.e diethyl chlorophosphate, diethyl cyanophosphonate, tris (2-chloroethyl) phosphate and dichlorvos). The organophosphates (OPs) form a covalent bond with -OH groups of SB and form SB-OP which quenches emission signal at 533 nm. Therefore, it can be used for the spectrofluorimetric detection and quantification of OPs upto the detection limits of 10.2, 158.2, 10.3 and 122.7 nM, respectively. Besides, the SB-OP duo undergoes degradation to non-toxic species in the presence of Zn2+ ions. The mechanism of interaction between SB-OP-Zn2+ trio is investigated by spectrofluorometric, spectroscopic, chromatographic and spectrometric experiments. The optimized recognition and degradation protocols were found accurate and precise when applied to fruits, vegetable and soil samples. Overall, the developed protocols prove SB as highly sensitive, selective and recyclable 'pick and degrade' probe for the recognition and degradation of OPs.


Assuntos
Retardadores de Chama/análise , Frutas/química , Organofosfatos/química , Verduras/química , Zinco/química , Cátions Bivalentes , Fosfatos , Bases de Schiff/química
9.
Proc Natl Acad Sci U S A ; 117(18): 9832-9839, 2020 05 05.
Artigo em Inglês | MEDLINE | ID: mdl-32317383

RESUMO

G-quadruplex, assembled from a square array of guanine (G) molecules, is an important structure with crucial biological roles in vivo but also a versatile template for ordered functional materials. Although the understanding of G-quadruplex structures is the focus of numerous studies, little is known regarding the control of G-quartet stacking modes and the spontaneous orientation of G-quadruplex fibrils. Here, the effects of different metal ions and their concentrations on stacking modes of G-quartets are elucidated. Monovalent cations (typically K+) facilitate the formation of G-quadruplex hydrogels with both heteropolar and homopolar stacking modes, showing weak mechanical strength. In contrast, divalent metal ions (Ca2+, Sr2+, and Ba2+) at given concentrations can control G-quartet stacking modes and increase the mechanical rigidity of the resulting hydrogels through ionic bridge effects between divalent ions and borate. We show that for Ca2+ and Ba2+ at suitable concentrations, the assembly of G-quadruplexes results in the establishment of a mesoscopic chirality of the fibrils with a regular left-handed twist. Finally, we report the discovery of nematic tactoids self-assembled from G-quadruplex fibrils characterized by homeotropic fibril alignment with respect to the interface. We use the Frank-Oseen elastic energy and the Rapini-Papoular anisotropic surface energy to rationalize two different configurations of the tactoids. These results deepen our understanding of G-quadruplex structures and G-quadruplex fibrils, paving the way for their use in self-assembly and biomaterials.


Assuntos
DNA/química , Quadruplex G , Guanina/química , Hidrogéis/química , Anisotropia , Cátions Bivalentes/química , Cátions Monovalentes/química , DNA/ultraestrutura , Metabolismo Energético/efeitos dos fármacos , Líquidos Iônicos/química , Íons/química , Metais/química , Conformação de Ácido Nucleico/efeitos dos fármacos , Propriedades de Superfície
10.
Chemosphere ; 249: 126564, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32213389

RESUMO

Pb-based perovskite nanoparticles (PbPNPs) are amongst others used within highly efficient solar cells. PbPNPs can be released into the environment during their production, recycling or waste processing. In this study we investigated the fate and toxicity of PbPNPs on soil bacterial community under simulated natural environmental conditions across a range of pH, humic acid, and divalent cation concentrations. Increasing pH decreased PbPNPs-particle aggregation as well as Pb-ion release. The presence of only humic acid (HA) prevented the aggregation of PbPNPs-particles, whereas the presence of only divalent cations promoted the aggregation of PbPNPs-particles. The amount of Pb-ions released from the PbPNPs-particles was reduced in the presence of either HA or the divalent cations. Results of toxicity testing of PbPNPs by determining the metabolic potential of a bacterial community indicated that increasing pH alleviated particle toxicity. The presence of only HA reduced the toxicity of PbPNPs, while the presence of only divalent cations enhanced the particle toxicity. The coexistence of HA and divalent cations enhanced PbPNPs aggregation and reduced toxicity, with both Pb-ions and the interaction between the PbPNPs-particles and bacterial cells contributing to the toxic effects. Our study emphasized that environmental conditions play important roles that influencing the fate and toxicity of PbPNPs.


Assuntos
Bactérias/efeitos dos fármacos , Compostos de Cálcio/química , Nanopartículas/toxicidade , Óxidos/química , Microbiologia do Solo , Poluentes do Solo/toxicidade , Titânio/química , Cátions Bivalentes , Substâncias Húmicas/análise , Concentração de Íons de Hidrogênio , Íons , Chumbo , Solo , Poluentes do Solo/análise , Testes de Toxicidade
11.
Food Chem ; 320: 126623, 2020 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-32220707

RESUMO

A novel ratiometric fluorescence probe was proposed for detecting lead (II) ions (Pb2+) in porphyra, the approach was based on copper nanoclusters and nitrogen-doped carbon quantum dots (CuNCs-CNQDs). In this probe, the CuNCs delivered the response signal, the fluorescence of which was enhanced by Pb2+ due to the aggregation-induced emission enhancement (AIEE) between Pb2+ and CuNCs. The CNQDs provided the self-calibration signal, whose fluorescence remained almost unchanged in coexistence with Pb2+. According to the change of fluorescence intensity ratio between the fluorophores, CuNCs-CNQDs nanohybrid was used as ratiometric probes for the sensitive detection of Pb2+ in the range of 0.010-2.5 mg L-1, with a detection limit of 0.0031 mg L-1. Finally, the probe was successfully applied to detect Pb2+ in porphyra with relative standard deviations (RSDs) lower than 5%. This study provides a straightforward, stable, and sensitive approach for detecting Pb2+ in porphyra.


Assuntos
Carbono/química , Cobre/química , Nitrogênio/química , Porphyra/química , Pontos Quânticos , Cátions Bivalentes/química , Fluorescência , Limite de Detecção , Nanoestruturas , Espectrometria de Fluorescência
12.
PLoS One ; 15(3): e0230327, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32150746

RESUMO

Sodium Calcium exchanger (NCX) proteins utilize the electrochemical gradient of Na+ to generate Ca2+ efflux (forward mode) or influx (reverse mode). In mammals, there are three unique NCX encoding genes-NCX1, NCX2, and NCX3, that comprise the SLC8A family, and mRNA from all three exchangers is expressed in hippocampal pyramidal cells. Furthermore, mutant ncx2-/- and ncx3-/- mice have each been shown to exhibit altered long-term potentiation (LTP) in the hippocampal CA1 region due to delayed Ca2+ clearance after depolarization that alters synaptic transmission. In addition to the role of NCX at the synapse of hippocampal subfields required for LTP, the three NCX isoforms have also been shown to localize to the dendrite of hippocampal pyramidal cells. In the case of NCX1, it has been shown to localize throughout the basal and apical dendrite of CA1 neurons where it helps compartmentalize Ca2+ between dendritic shafts and spines. Given the role for NCX and calcium in synaptic plasticity, the capacity of NCX splice-forms to influence backpropagating action potentials has clear consequences for the induction of spike-timing dependent synaptic plasticity (STDP). To explore this, we examined the effect of NCX localization, density, and allosteric activation on forward and back propagating signals and, next employed a STDP paradigm to monitor the effect of NCX on plasticity using back propagating action potentials paired with EPSPs. From our simulation studies we identified a role for the sodium calcium exchange current in normalizing STDP, and demonstrate that NCX is required at the postsynaptic site for this response. We also screened other mechanisms in our model and identified a role for the Ca2+ activated K+ current at the postsynapse in producing STDP responses. Together, our data reveal opposing roles for the Na+/Ca2+ exchanger current and the Ca2+ activated K+ current in setting STDP.


Assuntos
Região CA1 Hipocampal/fisiologia , Modelos Neurológicos , Plasticidade Neuronal/fisiologia , Células Piramidais/metabolismo , Trocador de Sódio e Cálcio/metabolismo , Potenciais de Ação/fisiologia , Animais , Região CA1 Hipocampal/citologia , Cálcio/metabolismo , Cátions Bivalentes/metabolismo , Cátions Monovalentes/metabolismo , Simulação por Computador , Modelos Animais , Potássio/metabolismo , Ratos , Sódio/metabolismo
13.
Nat Commun ; 11(1): 922, 2020 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-32066742

RESUMO

Ryanodine receptors (RyR) are ion channels responsible for the release of Ca2+ from the sarco/endoplasmic reticulum and play a crucial role in the precise control of Ca2+ concentration in the cytosol. The detailed permeation mechanism of Ca2+ through RyR is still elusive. By using molecular dynamics simulations with a specially designed Ca2+ model, we show that multiple Ca2+ ions accumulate in the upper selectivity filter of RyR1, but only one Ca2+ can occupy and translocate in the narrow pore at a time, assisted by electrostatic repulsion from the Ca2+ within the upper selectivity filter. The Ca2+ is nearly fully hydrated with the first solvation shell intact during the whole permeation process. These results suggest a remote knock-on permeation mechanism and one-at-a-time occupation pattern for the hydrated Ca2+ within the narrow pore, uncovering the basis underlying the high permeability and low selectivity of the RyR channels.


Assuntos
Sinalização do Cálcio , Cálcio/metabolismo , Cátions Bivalentes/metabolismo , Simulação de Dinâmica Molecular , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Cálcio/química , Calpaína/metabolismo , Cátions Bivalentes/química , Canal de Liberação de Cálcio do Receptor de Rianodina/química , Eletricidade Estática , Relação Estrutura-Atividade
14.
Environ Sci Technol ; 54(6): 3353-3362, 2020 03 17.
Artigo em Inglês | MEDLINE | ID: mdl-32083478

RESUMO

Although two-dimensional titanium carbide (Ti3C2Tx MXene) has emerged as a shining star material in various communities, its environmental behaviors and fate remain unknown. Herein, the colloidal properties and stability of Ti3C2Tx MXene are explored in aquatic systems for the first time, considering the roles of solution chemistry conditions (e.g., pH, ionic types, and strength). It was found that pH had no effect on the stability of Ti3C2Tx in the range of 5.0-11.0, whereas ionic valence and concentrations displayed significant effects on the aggregation behavior of Ti3C2Tx. By employing time-resolved dynamic light scattering measurements, the critical coagulation concentration (CCC) value of Ti3C2Tx was determined to be 12 mM for NaCl. The divalent cations Ca2+ and Mg2+ exhibited higher destabilizing capacity to Ti3C2Tx, as evidenced by the lower CCC values (0.3 and 0.4 mM for CaCl2 and MgCl2, respectively) and faster coagulation rates. Long-term stability studies implied that Ti3C2Tx MXene was less likely to be transported over long distances in the synthetic or natural waters. These findings provided significant insights into the fate and transport of Ti3C2Tx in the aquatic environment.


Assuntos
Cloreto de Sódio , Titânio , Cátions Bivalentes , Soluções
15.
Proc Natl Acad Sci U S A ; 117(10): 5291-5297, 2020 03 10.
Artigo em Inglês | MEDLINE | ID: mdl-32098845

RESUMO

Heterotropic allosteric activation of protein function, in which binding of one ligand thermodynamically activates the binding of another, different ligand or substrate, is a fundamental control mechanism in metabolism and as such has been a long-aspired capability in protein design. Here we show that greatly increasing the magnitude of a protein's net charge using surface supercharging transforms that protein into an allosteric ligand- and counterion-gated conformational molecular switch. To demonstrate this we first modified the designed helical bundle hemoprotein H4, creating a highly charged protein which both unfolds reversibly at low ionic strength and undergoes the ligand-induced folding transition commonly observed in signal transduction by intrinsically disordered proteins in biology. As a result of the high surface-charge density, ligand binding to this protein is allosterically activated up to 1,300-fold by low concentrations of divalent cations and the polyamine spermine. To extend this process further using a natural protein, we similarly modified Escherichia coli cytochrome b 562 and the resulting protein behaves in a like manner. These simple model systems not only establish a set of general engineering principles which can be used to convert natural and designed soluble proteins into allosteric molecular switches useful in biodesign, sensing, and synthetic biology, the behavior we have demonstrated--functional activation of supercharged intrinsically disordered proteins by low concentrations of multivalent ions--may be a control mechanism utilized by Nature which has yet to be appreciated.


Assuntos
Grupo dos Citocromos b/química , Proteínas de Escherichia coli/química , Hemeproteínas/química , Proteínas Intrinsicamente Desordenadas/química , Engenharia de Proteínas/métodos , Regulação Alostérica , Cálcio/química , Cátions Bivalentes/química , Ligantes , Magnésio/química , Conformação Proteica , Dobramento de Proteína , Espermina/química , Termodinâmica
16.
J Chem Theory Comput ; 16(3): 1913-1923, 2020 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-32059108

RESUMO

Divalent metal cations are essential for many biological processes; however, accurately modeling divalent metal ions has proved a significant challenge for molecular dynamics force fields. Here we show that the choice of ion model influences the observed dynamics in PsaA, a metal binding protein from Streptococcus pneumoniae. We conduct extensive unbiased simulations and free energy calculations of PsaA bound to its cognate ligand Mn2+ and inhibitory ligand Zn2+ using three nonbonded ion models: a 12-6 model, a 12-6-4 model, and a multisite model. The observed coordination geometries and metal binding dynamics are sensitive to the choice of ion model, with the most dramatic differences observed in free energy calculations of ion release. We show that the conformational ensemble of Mn-bound PsaA is more similar to the crystallographic metal bound open state. This work extends the current model of PsaA metal binding and provides a framework for the rationalization of experimentally determined metal binding behavior. Our findings support the use of the 12-6-4 ion model for further simulations of divalent cation binding proteins.


Assuntos
Proteínas de Transporte/metabolismo , Cátions Bivalentes/metabolismo , Metais/química , Streptococcus pneumoniae/química , Humanos , Conformação Molecular
17.
Int J Biol Macromol ; 148: 988-998, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-31972194

RESUMO

The present work elucidates achieving superior Cu(II) adsorption capacity using a facile protocol and a biodegradable material. Copper is one of the most prevalent metals used in industries, which creates severe health effects to the human and aquatic lives when present in excess. Cellulose sponge (CS) used as kitchen wipe was chosen and amine functionalities were introduced on it using ethylenediamine. Potentiality of the amine functionalized cellulose sponge (AF-CS) in Cu(II) removal is investigated for the first time. The batch adsorption parameters were optimized and various nonlinear kinetic and isotherm models were elaborately studied. The adsorption using CS and AF-CS behaved under a pseudo-second-order model and followed chemisorption. The maximum adsorption capacity values using AF-CS and CS from the Langmuir isotherm model were calculated to be 596.96 mg/g and 230.63 mg/g, respectively. Thence, AF-CS possesses proportionately higher adsorption capacity in comparison with CS due to the insertion of -NH2 groups. Further, the mechanism involved in the adsorption process was explored in detail through FESEM, FT-IR, FT-Raman and TGA analysis. The AF-CS sponge was stable on repeated use and retained 90% efficiency at the end of the 10th cycle. A highly effective, easily recyclable, biodegradable and cost-effective adsorbent has been synthesized possessing an extraordinarily high adsorption capacity towards Cu(II) ions.


Assuntos
Cátions Bivalentes/química , Celulose/química , Complexos de Coordenação/química , Cobre/química , Etilenodiaminas/química , Adsorção , Aminas/química , Dimetil Sulfóxido/química , Epicloroidrina/química , Concentração de Íons de Hidrogênio , Cinética , Modelos Químicos , Água , Poluentes Químicos da Água/química
18.
Talanta ; 209: 120569, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31892050

RESUMO

As the concentration of Zn2+ in patients with prostate cancer is much less than that in healthy persons, Zn2+ concentration can be used as a marker to expediently screen prostate cancer. In this study, a sensitive and highly selective surface-enhanced Raman scattering (SERS) method to detect Zn2+ concentration in human prostatic fluids by utilizing water-insoluble 2-carboxyl-2'-hydroxyl-5'-sulfoformazylbenze (Zincon) as a SERS probe based on self-assembled Au nanoarrays at a liquid-liquid interface between n-hexane and Au colloids was proposed. Zincon showed remarkably different SERS bands before and after coordinating Zn2+ in the controlled conditions (70 µL of ethanol, 500 µL of n-hexane, pH value of 7.1 and 10 s of vortex mixing time), which can be used in quantifying Zn2+ with characteristic peaks. The proposed SERS method presented a good linear relationship ranging from 0.5 to 10 µmol/L and a satisfactory detection limit of 0.1 µmol/L as well as low interference with other metal ions. Moreover, the detection results are close to those of the conventional standard atomic absorption spectroscopy (AAS) method.


Assuntos
Ouro/química , Nanoestruturas/química , Neoplasias da Próstata/diagnóstico , Análise Espectral Raman/métodos , Zinco/análise , Cátions Bivalentes/análise , Formazans/química , Humanos , Limite de Detecção , Masculino , Nanoestruturas/ultraestrutura , Próstata/química , Próstata/patologia , Neoplasias da Próstata/química , Neoplasias da Próstata/patologia
19.
Water Environ Res ; 92(5): 677-688, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31633854

RESUMO

The effect of mono- and divalent cation concentrations on digested sludge dewatering characteristics was investigated in a full-scale study at the Harrisonburg-Rockingham Regional Sewer Authority, VA (HRRSA) and at an additional POTW (POTW B). At HRRSA, anaerobic digesters were fed with primary sludge, enhanced biological phosphorus removal (EBPR) WAS, and trucked-in DAF solids from a poultry processing facility, and digested sludge was dewatered by belt filter press. The POTW B digesters received EBPR WAS and primary sludge, and dewatering was by centrifuge. Visual MINTEQ 3.1 (Gustafsson, 2014, Visual MINTEQ 3.1. User's manual) was used to determine cation speciation and struvite, tricalcium phosphate, vivianite, and ferrous sulfide formation at a range of digestion conditions. Significant Mg and Ca complexation was predicted at all conditions evaluated, and the majority of the complexes were monovalent cations. Complexation reduced the divalent cation concentration on the order of 40%. The HRRSA and POTW B data both showed that dewatered cake total solids (TS) increased linearly with uncomplexed divalent cation concentration and that there was an increase of 1.0%-1.1% TS for every additional 1.0 meq/L of uncomplexed divalent cations. Because POTW B used centrifuge dewatering, this relationship could be independent of dewatering technique. Further, the relationship between uncomplexed divalent cation concentration and dewaterability suggests that the selectivity of exocellular polymeric substances cation exchange sites is much greater for divalent cations so that monovalent cations only bind to them when their concentrations are much higher than those of the uncomplexed divalent cations. Thus, monovalent cation concentration may not be important in anaerobic digestion or other high alkalinity environments. PRACTITIONER POINTS: It is important to account for complexation in high alkalinity environments such as anaerobic digesters; The findings of this study suggest that dewatering characteristics of anaerobically digested enhanced biological phosphorus removal (EBPR) waste sludge can be significantly improved by preserving cation-mediated exocellular polymeric substances bonding in the solids stream by reducing struvite formation; Data from two full-scale POTW's indicated that dewatered cake TS was increased by 1.0%-1.1% for every 1.0 meq/L of dissolved uncomplexed divalent cations in the anaerobic digestate bulk solution; This relationship existed for dewatering both by a belt filter press and by a centrifuge suggesting that this relationship is independent of dewatering technology; Dissolved monovalent cation concentrations may not be important in anaerobic digestion or other high alkalinity environments unless their concentrations are much greater than those of the dissolved divalent cations.


Assuntos
Fósforo , Esgotos , Cátions Bivalentes , Estruvita , Eliminação de Resíduos Líquidos
20.
RNA ; 26(2): 111-125, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31776179

RESUMO

We develop an L-platform/L-scaffold framework we hypothesize may serve as a blueprint to facilitate site-specific RNA-cleaving nucleic acid enzyme design. Building on the L-platform motif originally described by Suslov and coworkers, we identify new critical scaffolding elements required to anchor a conserved general base guanine ("L-anchor") and bind functionally important metal ions at the active site ("L-pocket"). Molecular simulations, together with a broad range of experimental structural and functional data, connect the L-platform/L-scaffold elements to necessary and sufficient conditions for catalytic activity. We demonstrate that the L-platform/L-scaffold framework is common to five of the nine currently known naturally occurring ribozyme classes (Twr, HPr, VSr, HHr, Psr), and intriguingly from a design perspective, the framework also appears in an artificially engineered DNAzyme (8-17dz). The flexibility of the L-platform/L-scaffold framework is illustrated on these systems, highlighting modularity and trends in the variety of known general acid moieties that are supported. These trends give rise to two distinct catalytic paradigms, building on the classifications proposed by Wilson and coworkers and named for the implicated general base and acid. The "G + A" paradigm (Twr, HPr, VSr) exclusively utilizes nucleobase residues for chemistry, and the "G + M + " paradigm (HHr, 8-17dz, Psr) involves structuring of the "L-pocket" metal ion binding site for recruitment of a divalent metal ion that plays an active role in the chemical steps of the reaction. Finally, the modularity of the L-platform/L-scaffold framework is illustrated in the VS ribozyme where the "L-pocket" assumes the functional role of the "L-anchor" element, highlighting a distinct mechanism, but one that is functionally linked with the hammerhead ribozyme.


Assuntos
Engenharia Genética , Motivos de Nucleotídeos/genética , RNA Catalítico/genética , Catálise , Domínio Catalítico , Cátions Bivalentes/metabolismo , RNA/genética , RNA Catalítico/metabolismo
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