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1.
Nat Commun ; 11(1): 4372, 2020 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-32873801

RESUMO

3D molecular structure determination is a challenge for organic compounds or natural products available in minute amounts. Proton/proton and proton/carbon correlations yield the constitution. J couplings and NOEs oftentimes supported by one-bond 1H,13C residual dipolar couplings (RDCs) or by 13C residual chemical shift anisotropies (RCSAs) provide the relative configuration. However, these RDCs or carbon RCSAs rely on 1% natural abundance of 13C preventing their use for compounds available only in quantities of a few 10's of µgs. By contrast, 1H RCSAs provide similar information on spatial orientation of structural moieties within a molecule, while using the abundant 1H spin. Herein, 1H RCSAs are accurately measured using constrained aligning gels or liquid crystals and applied to the 3D structural determination of molecules with varying complexities. Even more, deuterated alignment media allow the elucidation of the relative configuration of around 35 µg of a briarane compound isolated from Briareum asbestinum.


Assuntos
Antozoários/química , Produtos Biológicos/química , Diterpenos/química , Conformação Molecular , Prótons , Animais , Anisotropia , Espectroscopia de Prótons por Ressonância Magnética
2.
J Chem Phys ; 153(11): 115101, 2020 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-32962355

RESUMO

Broad-spectrum antiviral drugs are urgently needed to stop the Coronavirus Disease 2019 pandemic and prevent future ones. The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is related to the SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV), which have caused the previous outbreaks. The papain-like protease (PLpro) is an attractive drug target due to its essential roles in the viral life cycle. As a cysteine protease, PLpro is rich in cysteines and histidines, and their protonation/deprotonation modulates catalysis and conformational plasticity. Here, we report the pKa calculations and assessment of the proton-coupled conformational dynamics of SARS-CoV-2 in comparison to SARS-CoV and MERS-CoV PLpros using the recently developed graphical processing unit (GPU)-accelerated implicit-solvent continuous constant pH molecular dynamics method with a new asynchronous replica-exchange scheme, which allows computation on a single GPU card. The calculated pKa's support the catalytic roles of the Cys-His-Asp triad. We also found that several residues can switch protonation states at physiological pH among which is C270/271 located on the flexible blocking loop 2 (BL2) of SARS-CoV-2/CoV PLpro. Simulations revealed that the BL2 can open and close depending on the protonation state of C271/270, consistent with the most recent crystal structure evidence. Interestingly, despite the lack of an analogous cysteine, BL2 in MERS-CoV PLpro is also very flexible, challenging a current hypothesis. These findings are supported by the all-atom fixed-charge simulations and provide a starting point for more detailed studies to assist the structure-based design of broad-spectrum inhibitors against CoV PLpros.


Assuntos
Antivirais/farmacologia , Betacoronavirus/enzimologia , Desenho de Fármacos , Coronavírus da Síndrome Respiratória do Oriente Médio/enzimologia , Simulação de Dinâmica Molecular , Papaína/química , Papaína/metabolismo , Prótons , Sequência de Aminoácidos , Histidina , Concentração de Íons de Hidrogênio , Papaína/antagonistas & inibidores , Domínios Proteicos
3.
Science ; 369(6508): 1160-1161, 2020 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-32883846
4.
Proc Biol Sci ; 287(1934): 20201506, 2020 09 09.
Artigo em Inglês | MEDLINE | ID: mdl-32900308

RESUMO

The sea urchin embryo develops a calcitic endoskeleton through intracellular formation of amorphous calcium carbonate (ACC). Intracellular precipitation of ACC, requires [Formula: see text] concentrating as well as proton export mechanisms to promote calcification. These processes are of fundamental importance in biological mineralization, but remain largely unexplored. Here, we demonstrate that the calcifying primary mesenchyme cells (PMCs) use Na+/H+-exchange (NHE) mechanisms to control cellular pH homeostasis during maintenance of the skeleton. During skeleton re-calcification, pHi of PMCs is increased accompanied by substantial elevation in intracellular [Formula: see text] mediated by the [Formula: see text] cotransporter Sp_Slc4a10. However, PMCs lower their pHi regulatory capacities associated with a reduction in NHE activity. Live-cell imaging using green fluorescent protein reporter constructs in combination with intravesicular pH measurements demonstrated alkaline and acidic populations of vesicles in PMCs and extensive trafficking of large V-type H+-ATPase (VHA)-rich acidic vesicles in blastocoelar filopodial cells. Pharmacological and gene expression analyses underline a central role of the VHA isoforms Sp_ATP6V0a1, Sp_ATP6V01_1 and Sp_ATPa1-4 for the process of skeleton re-calcification. These results highlight novel pH regulatory strategies in calcifying cells of a marine species with important implications for our understanding of the mineralization process in times of rapid changes in oceanic pH.


Assuntos
Bicarbonatos/metabolismo , Ouriços-do-Mar/fisiologia , Animais , Transporte Biológico , Calcificação Fisiológica , Carbonato de Cálcio , Concentração de Íons de Hidrogênio , Oceanos e Mares , Prótons , Água do Mar
5.
Nat Commun ; 11(1): 4722, 2020 09 18.
Artigo em Inglês | MEDLINE | ID: mdl-32948764

RESUMO

Precisely controlled deuterium labeling at specific sites of N-alkyl drugs is crucial in drug-development as over 50% of the top-selling drugs contain N-alkyl groups, in which it is very challenging to selectively replace protons with deuterium atoms. With the goal of achieving controllable isotope-labeling in N-alkylated amines, we herein rationally design photocatalytic water-splitting to furnish [H] or [D] and isotope alkanol-oxidation by photoexcited electron-hole pairs on a polymeric semiconductor. The controlled installation of N-CH3, -CDH2, -CD2H, -CD3, and -13CH3 groups into pharmaceutical amines thus has been demonstrated by tuning isotopic water and methanol. More than 50 examples with a wide range of functionalities are presented, demonstrating the universal applicability and mildness of this strategy. Gram-scale production has been realized, paving the way for the practical photosynthesis of pharmaceuticals.


Assuntos
Aminas/química , Aminas/metabolismo , Luz , Semicondutores , Alquilação , Aminas/farmacologia , Catálise , Deutério , Oxirredução , Preparações Farmacêuticas , Prótons , Água , Difração de Raios X
6.
Zhonghua Kou Qiang Yi Xue Za Zhi ; 55(8): 595-598, 2020 Aug 09.
Artigo em Chinês | MEDLINE | ID: mdl-32842353

RESUMO

Magnetic resonance imaging is most frequently used for pre-surgical diagnosis and follow-up in salivary gland neoplasms. As for traditional techniques, dynamic contrast-enhanced and diffusion-weighted imaging are two magnetic resonance sequences commonly used in clinic, in spite of their relatively lower sensitivity and specificity. Recently, a novel magnetic resonance technique, amide proton transfer-MRI (APT-MRI), gets a lot of attention due to its special imaging principle and higher sensitivity and specificity for many human tumors diagnosis. Moreover, some studies applied this new MRI technique successfully to the diagnosis and differential diagnosis of salivary gland neoplasms. In this review, we are going to focus on the basic principle of APT-MRI and its clinical applications in salivary gland neoplasms, with a comparison of traditional MRI sequences. We will also give some prospects based on these preliminary applications in APT-MRI diagnosis for salivary gland neoplasms.


Assuntos
Imagem por Ressonância Magnética , Neoplasias das Glândulas Salivares/diagnóstico por imagem , Amidas , Imagem de Difusão por Ressonância Magnética , Humanos , Prótons
7.
Nat Commun ; 11(1): 4135, 2020 08 18.
Artigo em Inglês | MEDLINE | ID: mdl-32811817

RESUMO

Complex I is the first and the largest enzyme of respiratory chains in bacteria and mitochondria. The mechanism which couples spatially separated transfer of electrons to proton translocation in complex I is not known. Here we report five crystal structures of T. thermophilus enzyme in complex with NADH or quinone-like compounds. We also determined cryo-EM structures of major and minor native states of the complex, differing in the position of the peripheral arm. Crystal structures show that binding of quinone-like compounds (but not of NADH) leads to a related global conformational change, accompanied by local re-arrangements propagating from the quinone site to the nearest proton channel. Normal mode and molecular dynamics analyses indicate that these are likely to represent the first steps in the proton translocation mechanism. Our results suggest that quinone binding and chemistry play a key role in the coupling mechanism of complex I.


Assuntos
Complexo I de Transporte de Elétrons/química , Simulação de Dinâmica Molecular , Quinonas/química , Thermus thermophilus/enzimologia , Regulação Alostérica , Proteínas de Bactérias/química , Microscopia Crioeletrônica , Cristalografia por Raios X , Transporte de Elétrons/genética , Complexo I de Transporte de Elétrons/genética , Complexo I de Transporte de Elétrons/metabolismo , Complexo I de Transporte de Elétrons/ultraestrutura , Modelos Moleculares , NAD/química , NAD/metabolismo , Redes Neurais de Computação , Conformação Proteica , Prótons , Quinonas/metabolismo , Thermus thermophilus/genética
8.
Environ Pollut ; 265(Pt B): 114628, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32806440

RESUMO

Volatile organic compounds (VOCs) are important precursors of ozone (O3) and secondary organic aerosols (SOAs). Tracing VOC pollution sources is important for controlling VOC emissions and reducing O3 and SOAs. We built a novel mobile proton transfer reaction mass spectrometry (M-PTR-MS) instrument to image the distribution of VOCs and trace their emission sources in cities and industrial parks. The M-PTR-MS is composed of a vibration-resistant proton transfer reaction mass spectrometry (PTR-MS) with a global positioning system receiver, modified box vehicle, and geographic information system (GIS) software. The PTR-MS, mounted on a vehicle, sends VOC data and vehicle position information to the GIS software. These data are used to image the space distribution of VOCs in real time while the vehicle platform is in motion and the VOC sources are precisely traced using the GIS. The spatial data resolution of the M-PTR-MS is typically 0.8 m. The limits of detection, sensitivity, and repeatability of the M-PTR-MS are 43.5 ppt, 347 counts ppb-1, and 2.4% (RSD, n = 5), respectively. The intensity of reagent ions is stable over 8 h (RSD = 0.45%). Compared with commercial PTR-MS equipment, the M-PTR-MS demonstrated high consistency, with a correlation coefficient of 92.665%. Several field experiments were conducted in China using the M-PTR-MS. In one field experiment, the VOC distribution along three different routes was surveyed; the navigation monitoring lasted 1.8 h over a distance of 26.7 km at an average speed of 15 km h-1. The VOC sources in an industrial park were identified by analyzing the components near different factories. The main species from a VOC source in an underground garage was related to paint. The M-PTR-MS instrument can be used by environmental protection agencies to trace VOC pollution sources in real time, and by researchers to survey VOC emissions in regions of concern.


Assuntos
Compostos Orgânicos Voláteis , China , Cidades , Espectrometria de Massas , Prótons
9.
Science ; 369(6503): 504-505, 2020 07 31.
Artigo em Inglês | MEDLINE | ID: mdl-32732409
10.
Proc Natl Acad Sci U S A ; 117(34): 20520-20529, 2020 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-32796105

RESUMO

As paradigms for proton-coupled electron transfer in enzymes and benchmarks for a fully renewable H2 technology, [FeFe]-hydrogenases behave as highly reversible electrocatalysts when immobilized on an electrode, operating in both catalytic directions with minimal overpotential requirement. Using the [FeFe]-hydrogenases from Clostridium pasteurianum (CpI) and Chlamydomonas reinhardtii (CrHydA1) we have conducted site-directed mutagenesis and protein film electrochemistry to determine how efficient catalysis depends on the long-range coupling of electron and proton transfer steps. Importantly, the electron and proton transfer pathways in [FeFe]-hydrogenases are well separated from each other in space. Variants with conservative substitutions (glutamate to aspartate) in either of two positions in the proton-transfer pathway retain significant activity and reveal the consequences of slowing down proton transfer for both catalytic directions over a wide range of pH and potential values. Proton reduction in the variants is impaired mainly by limiting the turnover rate, which drops sharply as the pH is raised, showing that proton capture from bulk solvent becomes critical. In contrast, hydrogen oxidation is affected in two ways: by limiting the turnover rate and by a large overpotential requirement that increases as the pH is raised, consistent with the accumulation of a reduced and protonated intermediate. A unique observation having fundamental significance is made under conditions where the variants still retain sufficient catalytic activity in both directions: An inflection appears as the catalytic current switches direction at the 2H+/H2 thermodynamic potential, clearly signaling a departure from electrocatalytic reversibility as electron and proton transfers begin to be decoupled.


Assuntos
Hidrogenase/metabolismo , Proteínas com Ferro-Enxofre/metabolismo , Chlamydomonas reinhardtii , Clostridium , Transporte de Elétrons , Hidrogenase/genética , Proteínas com Ferro-Enxofre/genética , Mutagênese Sítio-Dirigida , Prótons
11.
Nat Commun ; 11(1): 3921, 2020 08 06.
Artigo em Inglês | MEDLINE | ID: mdl-32764564

RESUMO

The vacuolar-type H+-ATPases (V-ATPase) hydrolyze ATP to pump protons across the plasma or intracellular membrane, secreting acids to the lumen or acidifying intracellular compartments. It has been implicated in tumor metastasis, renal tubular acidosis, and osteoporosis. Here, we report two cryo-EM structures of the intact V-ATPase from bovine brain with all the subunits including the subunit H, which is essential for ATPase activity. Two type-I transmembrane proteins, Ac45 and (pro)renin receptor, along with subunit c", constitute the core of the c-ring. Three different conformations of A/B heterodimers suggest a mechanism for ATP hydrolysis that triggers a rotation of subunits DF, inducing spinning of subunit d with respect to the entire c-ring. Moreover, many lipid molecules have been observed in the Vo domain to mediate the interactions between subunit c, c", (pro)renin receptor, and Ac45. These two structures reveal unique features of mammalian V-ATPase and suggest a mechanism of V1-Vo torque transmission.


Assuntos
Encéfalo/enzimologia , ATPases Vacuolares Próton-Translocadoras/química , Trifosfato de Adenosina/metabolismo , Animais , Bovinos , Microscopia Crioeletrônica , Hidrólise , Modelos Moleculares , Domínios e Motivos de Interação entre Proteínas , Multimerização Proteica , Estrutura Quaternária de Proteína , Subunidades Proteicas , Prótons , ATPases Vacuolares Próton-Translocadoras/metabolismo , ATPases Vacuolares Próton-Translocadoras/ultraestrutura
12.
Sci Total Environ ; 746: 140853, 2020 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-32745869

RESUMO

As an important part of biochar, surface functional group is the key interface between biochars and other phases, as well as an essential source of biochar's alkalinity and buffer abilities. However, due to the intricate organic and inorganic structures within biochars, the contribution from organic and inorganic matters to the functional groups remains unknown. In this work, the proton uptake curves were applied to study the functional groups of biochars via titration. Pine needle (PN) derived biochars with low inorganic content was selected for analyzing the organic functional groups variation under different pyrolysis temperatures. While rice straw (RS) derived biochars and the double-acid treated rice straw (DRS) derived biochars were compared for understanding the contributions from inorganic matters. The results indicate that the sorption behavior of proton onto biochars is surface adsorption, and the functional groups variation within PN biochars keeps consistent with reactions happened during pyrolysis. The inorganic matters within RS biochars contributed significantly to the buffering ability of biochars, and it is noteworthy to find that the contribution of inorganic matters of RS350, RS500, and RS700 on the total proton uptake stabilized at 67%, 84%, and 84% in the pH range of 2-8, respectively. As far as we know, this is the first report on separating the proton uptake ability of the organic and inorganic matters for biochars. The study on the interaction between biochars and proton will improve the estimation of the fate of ionizable pollutants, and the differentiation on the organic and inorganic matter contributions would benefit the understanding of biochar organic structures and inorganic structures.


Assuntos
Carvão Vegetal , Pirólise , Adsorção , Prótons , Temperatura
13.
PLoS One ; 15(8): e0237358, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32790705

RESUMO

OBJECTIVE: To clarify the relationship between amide proton transfer-weighted (APTW) signal, which reflects intracellular pH, and clinico-radiological findings in patients with hyperacute to subacute cerebral infarction. MATERIALS AND METHODS: Twenty-nine patients (median age, 70 years [IQR, 54 to 74]; 15 men) were retrospectively examined. The 10th, 25th, 50th, 75th, and 90th percentiles of APTW signal (APT10, APT25, APT50, APT75 and APT90, respectively) were measured within the infarction region-of-interest (ROI), and compared between poor prognosis and good prognosis groups (modified Rankin Scale [mRS] score ≥2 and mRS score <2, respectively). Correlations between APTW signal and time after onset, lesion size, National Institutes of Health Stroke Scale (NIHSS) score, mRS score, and mean apparent diffusion coefficient (ADC) were evaluated. RESULTS: The poor prognosis group had lower APT50, APT75, and APT90 than the good prognosis group (-0.66 [-1.19 to -0.27] vs. -0.09 [-0.62 to -0.21]; -0.27 [-0.63 to -0.01] vs. 0.31 [-0.15 to 1.06]; 0.06 [-0.21 to 0.34] vs. 0.93 [0.36 to 1.50] %; p <0.05, respectively). APT50 was positively correlated with time after onset (r = 0.37, p = 0.0471) and negatively with lesion size (r = -0.39, p = 0.0388). APT75 and APT90 were negatively correlated with NIHSS (r = -0.41 and -0.43; p <0.05, respectively). APT50, APT75 and APT90 were negatively correlated with mRS (r = -0.37, -0.52 and -0.57; p <0.05, respectively). APT10 and APT25 were positively correlated with mean ADC (r = 0.37 and 0.38; p <0.05, respectively). CONCLUSION: We demonstrated correlations between APTW signals of infarctions and clinico-radiological findings in patients with hyperacute to subacute infarctions. The poor prognosis group had a lower APTW signal than the good prognosis group. APTW signal was reduced in large infarctions, infarctions with low ADC, and in patients with high NIHSS and mRS scores.


Assuntos
Infarto Cerebral/diagnóstico , Imagem por Ressonância Magnética/métodos , Adulto , Idoso , Amidas/química , Encéfalo/diagnóstico por imagem , Infarto Cerebral/diagnóstico por imagem , Feminino , Humanos , Interpretação de Imagem Assistida por Computador , Masculino , Pessoa de Meia-Idade , Prognóstico , Prótons , Estudos Retrospectivos
14.
Nat Commun ; 11(1): 3888, 2020 08 04.
Artigo em Inglês | MEDLINE | ID: mdl-32753666

RESUMO

First proposed as antimicrobial agents, histones were later recognized for their role in condensing chromosomes. Histone antimicrobial activity has been reported in innate immune responses. However, how histones kill bacteria has remained elusive. The co-localization of histones with antimicrobial peptides (AMPs) in immune cells suggests that histones may be part of a larger antimicrobial mechanism in vivo. Here we report that histone H2A enters E. coli and S. aureus through membrane pores formed by the AMPs LL-37 and magainin-2. H2A enhances AMP-induced pores, depolarizes the bacterial membrane potential, and impairs membrane recovery. Inside the cytoplasm, H2A reorganizes bacterial chromosomal DNA and inhibits global transcription. Whereas bacteria recover from the pore-forming effects of LL-37, the concomitant effects of H2A and LL-37 are irrecoverable. Their combination constitutes a positive feedback loop that exponentially amplifies their antimicrobial activities, causing antimicrobial synergy. More generally, treatment with H2A and the pore-forming antibiotic polymyxin B completely eradicates bacterial growth.


Assuntos
Anti-Infecciosos/farmacologia , Bactérias/efeitos dos fármacos , Bactérias/genética , Estruturas Cromossômicas/efeitos dos fármacos , Histonas/metabolismo , Prótons , Animais , Estruturas Cromossômicas/metabolismo , Cromossomos Bacterianos/metabolismo , DNA Bacteriano/metabolismo , Sinergismo Farmacológico , Escherichia coli/efeitos dos fármacos , Escherichia coli/metabolismo , Imunidade Inata , Mamíferos , Polimixina B/farmacologia , Análise de Sequência de RNA , Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/metabolismo
15.
Water Res ; 185: 116272, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32810743

RESUMO

Algogenic organic matter (AOM) produced by Microcystis cells inhibits coagulation harvesting; however, the harvesting inhibitory mechanisms at the functional groups level remain to be determined. This study fractionated extracellular organic matter (EOM) and intercellular organic matter (IOM) from Microcystis flos-aquae into five different hydrophilic and hydrophobic fractions and investigated their inhibition of chitosan coagulation harvesting. The proton-active functional groups in the inhibitory fractions were further analysed by potentiometric titration, and the interaction between these functional groups and chitosan was elucidated. The results showed that the harvesting inhibition of M. flos-aquae cells was dominated by HPI in AOM due to its high charge density, which resulted in greater consumption of coagulant. Potentiometric titration results suggested that the proton-active functional groups of both HPIEOM and HPIIOM consist mainly of phosphodiester, carboxylic, phosphoryl and amine/hydroxyl functional groups, and the harvesting inhibition of HPI on M. flos-aquae cells at pH 6.5 was mainly due to the deprotonation of phosphodiester and carboxylic functional groups. Moreover, carboxylic functional groups with stronger polarity could enhance the intermolecular interaction between HPI and chitosan more effectively than phosphodiester at pH 6.5. Preventing the deprotonation of carboxylic functional groups by adjusting the pH to 4.3 could effectively alleviate the harvesting inhibition caused by HPI. These findings revealed the inhibition mechanism of AOM on the coagulation harvesting of M. flos-aquae cells from the perspective of deprotonation of proton-active functional groups, which may provide important insights for assessing the role of AOM in the coagulation harvesting of Microcystis cells.


Assuntos
Quitosana , Microcystis , Prótons
16.
Arch Biochem Biophys ; 690: 108474, 2020 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-32687799

RESUMO

Kynurenine 3-monoxygenase (KMO) catalyzes the conversion of l-kynurenine (L-Kyn) to 3-hydroxykynurenine (3-OHKyn) in the pathway for tryptophan catabolism. We have investigated the effects of pH and deuterium substitution on the oxidative half-reaction of KMO from P. fluorescens (PfKMO). The three phases observed during the oxidative half reaction are formation of the hydroperoxyflavin, hydroxylation and product release. The measured rate constants for these phases proved largely unchanging with pH, suggesting that the KMO active site is insulated from exchange with solvent during catalysis. A solvent inventory study indicated that a solvent isotope effect of 2-3 is observed for the hydroxylation phase and that two or more protons are in flight during this step. An inverse isotope effect of 0.84 ± 0.01 on the rate constant for the hydroxylation step with ring perdeutero-L-Kyn as a substrate indicates a shift from sp2 to sp3 hybridization in the transition state leading to the formation of a non-aromatic intermediate. The pH dependence of transient state data collected for the substrate analog meta-nitrobenzoylalanine indicate that groups proximal to the hydroperoxyflavin are titrated in the range pH 5-8.5 and can be described by a pKa of 8.8. That higher pH values do not slow the rate of hydroxylation precludes that the pKa measured pertains to the proton of the hydroperoxflavin. Together, these observations indicate that the C4a-hydroperoxyflavin has a pKa ≫ 8.5, that a non-aromatic species is the immediate product of hydroxylation and that at least two solvent derived protons are in-flight during oxygen insertion to the substrate aromatic ring. A unifying mechanistic proposal for these observations is proposed.


Assuntos
Hidrogênio/química , Quinurenina 3-Mono-Oxigenase/química , Quinurenina 3-Mono-Oxigenase/metabolismo , Cinurenina/química , Pseudomonas fluorescens/química , Catálise , Domínio Catalítico , Deutério/química , Dinitrocresóis/metabolismo , Flavinas/química , Concentração de Íons de Hidrogênio , Hidroxilação , Cinética , Oxigenases de Função Mista/metabolismo , Oxirredução , Estresse Oxidativo , Oxigênio/química , Prótons , Solventes/química
17.
Biochim Biophys Acta Bioenerg ; 1861(10): 148258, 2020 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-32619428

RESUMO

Upon a dark-to-light transition, multiple species of cyanobacteria release a certain amount of H+ from the inside to the outside of their cells. Previous studies revealed the plasma membrane-localizing Proton exchange A (PxcA) is involved in the light-induced H+ extrusion in the cyanobacterium Synechocystis sp. PCC6803. Among oxygenic phototrophs, two PxcA homologs are conserved; they are the nuclear-encoded Day-length-dependent delayed-greening1 (DLDG1) and the plastid-encoded Ycf10 in Arabidopsis thaliana. We previously identified the putative DLDG1/Ycf10-interacting protein, Fluctuating-light acclimation protein1 (FLAP1), required for pH regulation in Arabidopsis chloroplasts. Synechocystis has PxcA and FLAP1 homologs designated here as PxcA like (PxcL) and FLAP1 homolog A (FlpA). Synechocystis mutants lacking pxcA, pxcL, and flpA were constructed and characterized to gain more insight into regulatory mechanisms of light-induced H+ extrusion in cyanobacteria. pH change kinetics of the extracellular solvent after shifting Synechocystis cells from dark to light indicated that PxcA is essential for the light-induced H+ extrusion, and both PxcA and PxcL were involved in H+ uptake. Mutational loss of flpA resulted in altered PxcA- and PxcL-dependent H+ efflux/influx activities, and the flpA-null mutant showed inhibited growth under dark-light cycles, indicating the importance of FlpA function for photosynthetic growth under fluctuating light. Collectively, these data suggest that PxcA is involved in H+ efflux immediately after light irradiation for the rapid formation of the H+ concentration gradient across the thylakoid membranes, PxcL is involved in H+ influx for activation of the Calvin-Benson-Bassham cycle, and FlpA controls the H+ transport under fluctuating light.


Assuntos
Proteínas de Bactérias/metabolismo , Luz , Plastídeos/metabolismo , Prótons , Homologia de Sequência de Aminoácidos , Synechocystis/metabolismo , Synechocystis/efeitos da radiação , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Transporte Biológico/efeitos da radiação , Concentração de Íons de Hidrogênio , Mutação , Synechocystis/genética
18.
Phytochemistry ; 178: 112454, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32692658

RESUMO

Rooperol and its derivatives, derived from the Hypoxis rooperi plant, are polyphenolic and norlignan compounds with excellent antioxidant activities. The reaction enthalpies for the free-radical scavenging by rooperol and its six derivatives were studied using density functional theory. We found that the C-H groups played a significant role in the antioxidant activities in non-polar phases. In the gas and benzene phases, rooperol and its derivatives preferentially underwent the free-radical scavenging process via the 3‒CH group by following the hydrogen atom transfer (HAT) mechanism. In polar phases, the sequential proton loss electron transfer (SPLET) was the most preferred mechanism, and the phenolic O‒H groups played a significant role. Additionally, we found that when the hydrogen atom in the OH group was replaced by a glucose moiety, the antioxidant activity of the adjacent OH group was reduced. ROP, DHROP-I, DHROP-II, ROP-4″-G and ROP-4'G have catechol moiety, they may proceed double step-wise mechanisms to trap free radicals. In the gas and benzene phases, the preferable mechanism is dHAT. In water phase, it is SPLHAT.


Assuntos
Antioxidantes , Catecóis , Transporte de Elétrons , Prótons
20.
Science ; 369(6500): 138-139, 2020 07 10.
Artigo em Inglês | MEDLINE | ID: mdl-32646984
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