Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 8.908
Filtrar
1.
Nat Commun ; 11(1): 547, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31992706

RESUMO

TrkH is a bacterial ion channel implicated in K+ uptake and pH regulation. TrkH assembles with its regulatory protein, TrkA, which closes the channel when bound to ADP and opens it when bound to ATP. However, it is unknown how nucleotides control the gating of TrkH through TrkA. Here we report the structures of the TrkH-TrkA complex in the presence of ADP or ATP. TrkA forms a tetrameric ring when bound to ADP and constrains TrkH to a closed conformation. The TrkA ring splits into two TrkA dimers in the presence of ATP and releases the constraints on TrkH, resulting in an open channel conformation. Functional studies show that both the tetramer-to-dimer conversion of TrkA and the loss of constraints on TrkH are required for channel gating. In addition, deletion of TrkA in Escherichia coli depolarizes the cell, suggesting that the TrkH-TrkA complex couples changes in intracellular nucleotides to membrane potential.


Assuntos
Transportadores de Cassetes de Ligação de ATP/química , Transportadores de Cassetes de Ligação de ATP/metabolismo , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Potenciais da Membrana/fisiologia , Canais de Potássio/química , Canais de Potássio/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Difosfato de Adenosina , Trifosfato de Adenosina/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Transporte Biológico/fisiologia , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Modelos Moleculares , Mutagênese , Potássio/metabolismo , Canais de Potássio/genética , Conformação Proteica , Domínios e Motivos de Interação entre Proteínas , Deleção de Sequência , Vibrio parahaemolyticus/genética , Difração de Raios X
2.
Chemosphere ; 238: 124594, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31445334

RESUMO

Enhancing the biodegradation efficiency of atrazine, a kind of commonly applied herbicide, has been attracted much more concern. Here, Zn2+ which has long been considered essential in adjusting cell physiological status was selected to investigate its role on the biodegradation of atrazine by Arthrobacter sp. DNS10 as well as the transmembrane transport of atrazine during the biodegradation period. The results of gas chromatography showed that the atrazine removal percentages (initial concentration was 100 mg L-1) in 0.05 mM Zn2+ and 1.0 mM Zn2+ treatments were 94.42% and 86.02% respectively at 48 h, while there was also 66.43% of atrazine left in the treatment without exogenous Zn2+ existence. The expression of atrazine chlorohydrolase gene trzN in the strain DNS10 cultured with 0.05 mM and 1.0 mM Zn2+ was 7.30- and 4.67- times respectively compared with that of the non-zinc treatment. In addition, the flow cytometry test suggests that 0.05 mM of Zn2+ could better adjust the membrane permeability of strain DNS10, meanwhile, the amount of atrazine accumulation in the strain DNS10 co-cultured with this level Zn2+ was 2.21 times of that of the strain without Zn2+. This study may facilitate a better understanding of the mechanisms that exogenous Zn2+ enhances the biodegradation of atrazine by Arthrobacter sp. DNS10.


Assuntos
Arthrobacter/metabolismo , Atrazina/análise , Herbicidas/análise , Hidrolases/biossíntese , Zinco/farmacologia , Biodegradação Ambiental/efeitos dos fármacos , Transporte Biológico/fisiologia , Hidrolases/genética , Permeabilidade/efeitos dos fármacos , Microbiologia do Solo
3.
Res Microbiol ; 170(8): 345-357, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31678562

RESUMO

Iron acquisition is an essential aspect of cell physiology for most bacteria. Although much is known about how bacteria initially recognize the various iron sources they can encounter, whether siderophore, heme, host iron/heme binding proteins, much less is known about how the iron containing compounds (Fe2+, Fe3+, Fe3+-siderophore complex or heme) are transported across the cytoplasmic membrane. This last transport step is powered by specific ABC (ATP-Binding-Cassette) transporters, made up of a substrate binding protein (SBP) that delivers its cargo to the TMD (TransMembrane Domain) of the ABC transporter triggering the entry of the substrate inside the cytoplasm upon catalytic activity of the ABC module. This review focuses on structural aspects of the functioning of such ABC transporters with the most part devoted to the substrate binding proteins.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Bactérias/metabolismo , Compostos de Ferro/metabolismo , Transporte Biológico/fisiologia , Membrana Celular/metabolismo , Heme/metabolismo , Modelos Moleculares , Sideróforos/metabolismo
4.
Infect Immun ; 87(12)2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31570563

RESUMO

Bacteria use siderophores to scavenge iron from environmental or host sources. The iron acquisition systems of Chromobacterium violaceum, a ubiquitous environmental bacterium that can cause infections in humans, are still unknown. In this work, we demonstrated that C. violaceum produces putative distinct endogenous siderophores, here named chromobactin and viobactin, and showed that they are each required for iron uptake and virulence. An in silico analysis in the genome of C. violaceum revealed that genes related to synthesis and uptake of chromobactin (cba) and viobactin (vba) are located within two secondary-metabolite biosynthetic gene clusters. Using a combination of gene deletions and siderophore detection assays, we revealed that chromobactin and viobactin are catecholate siderophores synthesized from the common precursor 2,3-dihydroxybenzoate (2,3-DHB) on two nonribosomal peptide synthetase (NRPS) enzymes (CbaF and VbaF) and taken up by two TonB-dependent receptors (CbuA and VbuA). Infection assays in mice revealed that both the synthesis and the uptake of chromobactin or viobactin are required for the virulence of C. violaceum, since only the mutant strains that do not produce any siderophores or are unable to take up both of them were attenuated for virulence. In addition, the mutant strain unable to take up both siderophores showed a pronounced attenuation of virulence in vivo and reduced neutrophil extracellular trap (NET) formation in in vitro assays, suggesting that extracellularly accumulated siderophores modulate the host immune response. Overall, our results revealed that C. violaceum uses distinct endogenous siderophores for iron uptake and its establishment in the host.


Assuntos
Chromobacterium/genética , Chromobacterium/metabolismo , Ferro/metabolismo , Sideróforos/genética , Sideróforos/metabolismo , Animais , Transporte Biológico/fisiologia , Chromobacterium/patogenicidade , Armadilhas Extracelulares/metabolismo , Feminino , Hidroxibenzoatos/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Família Multigênica/genética , Neutrófilos/metabolismo , Peptídeo Sintases/metabolismo
5.
Res Microbiol ; 170(8): 321-337, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31560984

RESUMO

ATP-binding cassette (ABC) transporters use the energy of ATP hydrolysis to transport a large diversity of molecules actively across biological membranes. A combination of biochemical, biophysical, and structural studies has established the maltose transporter MalFGK2 as one of the best characterized proteins of the ABC family. MalF and MalG are the transmembrane domains, and two MalKs form a homodimer of nucleotide-binding domains. A periplasmic maltose-binding protein (MalE) delivers maltose and other maltodextrins to the transporter, and triggers its ATPase activity. Substrate import occurs in a unidirectional manner by ATP-driven conformational changes in MalK2 that allow alternating access of the substrate-binding site in MalF to each side of the membrane. In this review, we present an integrated molecular mechanism of the transport process considering all currently available information. Furthermore, we summarize remaining inconsistencies and outline possible future routes to decipher the full mechanistic details of transport by MalEFGK2 complex and that of related importer systems.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Trifosfato de Adenosina/metabolismo , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Maltose/metabolismo , Polissacarídeos/metabolismo , Sítios de Ligação , Transporte Biológico/fisiologia , Membrana Celular/metabolismo , Modelos Moleculares , Proteínas Periplásmicas de Ligação/metabolismo , Conformação Proteica
6.
Res Microbiol ; 170(8): 417-425, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31562919

RESUMO

ABC transporters of the Pleiotropic Drug Resistance (PDR) family are the main actors of antifungal resistance in pathogenic fungi. While their involvement in clinical resistant strains has been proven, their transport mechanism remains unclear. Notably, one hallmark of PDR transporters is their asymmetry, with one canonical nucleotide-binding site capable of ATP hydrolysis while the other site is not. Recent publications reviewed here show that the so-called "deviant" site is of crucial importance for drug transport and is a step towards alleviating the mystery around the existence of non-catalytic binding sites.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Antifúngicos/metabolismo , Candida albicans/metabolismo , Farmacorresistência Fúngica/fisiologia , Antifúngicos/farmacologia , Sítios de Ligação/fisiologia , Transporte Biológico/fisiologia , Candida albicans/efeitos dos fármacos , Candidíase/tratamento farmacológico , Candidíase/patologia , Humanos
7.
Nat Commun ; 10(1): 4276, 2019 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-31537798

RESUMO

Transport of dietary cholesterol from endocytic organelles to the endoplasmic reticulum (ER) is essential for cholesterol homoeostasis, but the mechanism and regulation of this transport remains poorly defined. Membrane contact sites (MCS), microdomains of close membrane apposition, are gaining attention as important platforms for non-vesicular, inter-organellar communication. Here we investigate the impact of ER-endocytic organelle MCS on cholesterol transport. We report a role for Niemann-Pick type C protein 1 (NPC1) in tethering ER-endocytic organelle MCS where it interacts with the ER-localised sterol transport protein Gramd1b to regulate cholesterol egress. We show that artificially tethering MCS rescues the cholesterol accumulation that characterises NPC1-deficient cells, consistent with direct lysosome to ER cholesterol transport across MCS. Finally, we identify an expanded population of lysosome-mitochondria MCS in cells depleted of NPC1 or Gramd1b that is dependent on the late endosomal sterol-binding protein STARD3, likely underlying the mitochondrial cholesterol accumulation in NPC1-deficient cells.


Assuntos
Transporte Biológico/fisiologia , Colesterol/metabolismo , Retículo Endoplasmático/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas de Membrana/metabolismo , Animais , Células CHO , Proteínas de Transporte/metabolismo , Linhagem Celular Tumoral , Cricetinae , Cricetulus , Células HeLa , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Lisossomos/metabolismo , Mitocôndrias/metabolismo , Doença de Niemann-Pick Tipo C/genética , Interferência de RNA , RNA Interferente Pequeno/genética
8.
Res Microbiol ; 170(8): 435-447, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31563533

RESUMO

The ATP binding cassette protein superfamily comprises ATPase enzymes which are, for the most part, involved in transmembrane transport. Within this superfamily however, some protein families have other functions unrelated to transport. One example is the ABC-F family, which comprises an extremely diverse set of cytoplasmic proteins. All of the proteins in the ABC-F family characterized to date act on the ribosome and are translation factors. Their common function is ATP-dependent modulation of the stereochemistry of the peptidyl transferase center (PTC) in the ribosome coupled to changes in its global conformation and P-site tRNA binding geometry. In this review, we give an overview of the function, structure, and theories for the mechanisms-of-action of microbial proteins in the ABC-F family, including those involved in mediating resistance to ribosome-binding antibiotics.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Farmacorresistência Bacteriana Múltipla/fisiologia , Escherichia coli/metabolismo , Biossíntese de Proteínas/efeitos dos fármacos , Ribossomos/efeitos dos fármacos , Transportadores de Cassetes de Ligação de ATP/genética , Antibacterianos/metabolismo , Antibacterianos/farmacologia , Transporte Biológico/fisiologia , Cristalografia por Raios X , Farmacorresistência Bacteriana Múltipla/genética , Biossíntese de Proteínas/genética , Conformação Proteica , Domínios Proteicos , Ribossomos/metabolismo
9.
Res Microbiol ; 170(8): 399-406, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31401108

RESUMO

Microcins and bacteriocins are ribosomally-synthesized defence peptides produced by Gram-negative and -positive bacteria to target competitors in their niche. Some of them carry posttranslational modifications established by dedicated enzymes. To protect themselves from their own toxic peptides, bacteria use dedicated immunity proteins or expel the toxin using ATP-binding cassette (ABC) transporters. In this last case, this immunity function is associated to export of the antimicrobial peptide out of the producing cells for targeting their competitors. Here we review the characteristics of these ABC-exporters and the mechanisms they use that unexpectedly cover from high promiscuity to high specificity or ensure another function concomitantly.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Peptídeos Catiônicos Antimicrobianos/metabolismo , Bacteriocinas/metabolismo , Bactérias Gram-Negativas/metabolismo , Bactérias Gram-Positivas/metabolismo , Antibacterianos/metabolismo , Bacteriocinas/genética , Transporte Biológico/fisiologia , Farmacorresistência Bacteriana/fisiologia
10.
Drug Deliv ; 26(1): 831-840, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31401887

RESUMO

Formulations for nasal drug delivery often rely on water sorption to adhere to the mucosa, which also causes a higher water gradient over the tissue and subsequent dehydration. The primary aim of this study was therefore to evaluate mucosal response to dehydration and resolve the hypothesis that mucoadhesion achieved through water sorption could also be a constraint for drug absorption via the nasal route. The effect of altering water activity of the vehicle on Xylometazoline HCl and 51Cr-EDTA uptake was studied separately ex vivo using flow through diffusion cells and excised porcine mucosa. We have shown that a modest increase in the water gradient over mucosa induces a substantial decrease in drug uptake for both Xylometazoline HCl and 51Cr-EDTA. A similar result was obtained when comparing two different vehicles on the market; Nasoferm® (Nordic Drugs, Sweden) and BLOX4® (Bioglan, Sweden). Mucoadhesion based on water sorption can slow down drug uptake in the nasal cavity. However, a clinical study is required to determine whether prolonged duration of the vehicle in situ or preventing dehydration of the mucosa is the most important factor for improving bioavailability.


Assuntos
Transporte Biológico/fisiologia , Desidratação/metabolismo , Desidratação/fisiopatologia , Mucosa Nasal/metabolismo , Preparações Farmacêuticas/metabolismo , Administração Intranasal/métodos , Animais , Disponibilidade Biológica , Sistemas de Liberação de Medicamentos/métodos , Excipientes/química , Suínos
11.
Drug Deliv ; 26(1): 841-848, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31401891

RESUMO

The purpose of this study was to compare the pharmacokinetic profile of tetramethylpyrazine hydrochloride (TMPH) in rat plasma and tissues following intravenous (iv), intragastric (ig) and intraocular (io) administration. After io, ig and iv administration of a single dose at 10 mg/kg, tissue and plasma samples drawn from the femoral artery were collected at timed intervals. The concentration of TMPH in the samples was analyzed using high-performance liquid chromatography (HPLC). The area under the concentration-time curve (AUC) and the drug targeting efficiency percentage (DTE(%)) were calculated to evaluate the targeting efficiency of the drug with the three different administration routes. After io administration, TMPH was rapidly absorbed to reach its peak plasma and brain concentration within 5 min. The systemic bioavailability obtained with io administration was greater than that obtained through the ig route (63.22% vs. 16.88%). The AUCt rank order of the iv administration group was AUCkidney >AUCheart >AUCliver >AUCbrain >AUCspleen >AUClung; that of the ig administration group as AUCkidney >AUCliver >AUCheart >AUCspleen >AUCbrain >AUClung; while that of the io administration group was AUCkidney >AUCbrain >AUCheart >AUCliver >AUCspleen >AUClung. The ratio of the AUCbrain value between the io route and iv injection was 1.05, which was greater than that obtained after ig administration (0.30). The DTE after io administration was calculated: brain (165.72%), heart (97.76%), liver (113.06%), spleen (105.31%), lung (163.40%) and kidney (135.31%). The io administration group showed obvious drug transport to the brain. These results indicate that TMPH is rapidly absorbed from the eye into the systemic circulation, and there may be a direct translocation pathway for TMPH from the eye to the brain. Therefore, io administration of TMPH could be a promising alternative to intravenous and oral approaches.


Assuntos
Encéfalo/efeitos dos fármacos , Pirazinas/administração & dosagem , Animais , Disponibilidade Biológica , Transporte Biológico/fisiologia , Sistemas de Liberação de Medicamentos/métodos , Injeções Intraoculares/métodos , Masculino , Ratos , Ratos Sprague-Dawley
12.
Nat Commun ; 10(1): 3564, 2019 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-31395861

RESUMO

In plants, plasmodesmata (PD) are nanopores that serve as channels for molecular cell-to-cell transport. Precise control of PD permeability is essential to regulate processes such as growth and tissue patterning, photoassimilate distribution and defense against pathogens. Callose deposition modulates PD transport but little is known of the rapid events that lead to PD closure in response to tissue damage or osmotic shock. We propose a mechanism of PD closure as a result of mechanosensing. Pressure forces acting on the dumbbell-shaped ER-desmotubule complex cause it to be displaced from its equilibrium position, thus closing the PD aperture. The filamentous protein tethers that link the plasma membrane to the ER-desmotubule complex play a key role in determining the selectivity of the PD pore. This model of PD control compares favorably with experimental data on the pressure-generated closure of PD.


Assuntos
Comunicação Celular/fisiologia , Permeabilidade da Membrana Celular/fisiologia , Mecanotransdução Celular , Fenômenos Fisiológicos Vegetais , Plasmodesmos/metabolismo , Transporte Biológico/fisiologia , Retículo Endoplasmático/metabolismo , Glucanos/metabolismo , Nanoporos , Pressão Osmótica/fisiologia
13.
Eur J Pharm Biopharm ; 143: 18-23, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31419586

RESUMO

Retinal pigment epithelium (RPE) is a major part of blood-retinal barrier that affects drug elimination from the vitreous to the blood and drug distribution from blood circulation into the eye. Even though drug clearance from the vitreous has been well studied, the role of RPE in the process has not been quantified. The aim of this work was to study the role of RPE clearance (CLRPE) as part of drug elimination from the vitreous and ocular drug distribution from the systemic blood circulation. We determined the bidirectional permeability of eight small molecular weight drugs and bevacizumab antibody across isolated bovine RPE-choroid. Permeability of small molecules was 10-6-10-5 cm/s showing 13-15 fold range of outward and inward permeation, while permeability of bevacizumab was lower by 2-3 orders of magnitude. Most small molecular weight drugs showed comparable outward (vitreous-to-choroid) and inward (choroid-to-vitreous) permeability across the RPE-choroid, except ciprofloxacin and ketorolac that had an over 6 and 14-fold higher outward than inward permeability, respectively, possibly indicating active transport. Six of seven tested small molecular weight drugs had outward CLRPE values that were comparable with their intravitreal clearance (CLIVT) values (0.84-2.6 fold difference). On the contrary, bevacizumab had an outward CLRPE that was only 3.5% of the CLIVT, proving that its main route of elimination (after intravitreal injection) is not RPE permeation. Experimental values were used in pharmacokinetic simulations to assess the role of the RPE in drug transfer from the systemic blood circulation to the vitreous (CLBV). We conclude that for small molecular weight drugs the RPE is an important route in drug transfer between the vitreal cavity and blood, whereas it effectively hinders the movement of bevacizumab from the vitreous to the systemic circulation.


Assuntos
Preparações Farmacêuticas/metabolismo , Segmento Posterior do Olho/metabolismo , Retina/metabolismo , Epitélio Pigmentado da Retina/metabolismo , Animais , Transporte Biológico/fisiologia , Transporte Biológico Ativo/fisiologia , Barreira Hematorretiniana/metabolismo , Bovinos , Corioide/metabolismo , Injeções Intravítreas , Taxa de Depuração Metabólica/fisiologia , Permeabilidade
14.
Res Microbiol ; 170(8): 392-398, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31442612

RESUMO

Multidrug transporters are important and interesting molecular machines that extrude a wide variety of cytotoxic drugs from target cells. This review summarizes novel insights in the energetics and mechanisms of bacterial ATP-binding cassette multidrug transporters as well as recent advances connecting multidrug transport to ion and lipid translocation processes in other membrane proteins.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Antibacterianos/metabolismo , Bactérias/metabolismo , Farmacorresistência Bacteriana Múltipla/fisiologia , Metabolismo Energético/fisiologia , Trifosfato de Adenosina/metabolismo , Antibacterianos/farmacologia , Transporte Biológico/fisiologia , Conformação Proteica
15.
Res Microbiol ; 170(8): 304-320, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31442613

RESUMO

This review will inevitably be influenced by my personal experience and personal view of the progression of this amazing family of proteins. This has generated a huge literature in over nearly five decades, some ideas have bloomed and faded while others have persisted, other contributions simply become redundant, overtaken by better techniques. At the outset, the pioneers had no idea of the magnitude of the topic they were working on, then a very rough idea of the significance emerged and, progressively, the picture becomes sharper and finally extraordinary. I have tried to produce at least an outline of that progression. My apologies for the also inevitable omissions, especially relating to the mass of biochemical and spectroscopy and genetical studies. I decided to prioritise structural biology because structures when successful are definitive and of course provide a 'visual' image. However, I tried to limit the structural aspects to the proteins that reflected the main advances.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Trifosfato de Adenosina/metabolismo , Antibacterianos/metabolismo , Bactérias/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Transporte Biológico/fisiologia , Farmacorresistência Bacteriana/genética , Farmacorresistência Bacteriana/fisiologia , Metabolismo dos Lipídeos/fisiologia , Conformação Proteica
16.
Res Microbiol ; 170(8): 366-373, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31376484

RESUMO

The surface of the outer membrane of Gram-negative bacteria is covered by a tightly packed layer of lipopolysaccharide molecules which provide a barrier against many toxic compounds and antibiotics. Lipopolysaccharide, synthesized in the cytoplasm, is assembled in the periplasmic leaflet of the inner membrane where the intermembrane Lpt system mediates its transport to the cell surface. The first step of lipopolysaccharide transport is its extraction from the outer leaflet of inner membrane powered by the atypical LptB2FGC ABC transporter. Here we review latest advances leading to understanding at molecular level how lipopolysaccharide is transported irreversibly to the outer membrane.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Escherichia coli/metabolismo , Lipopolissacarídeos/metabolismo , Proteínas da Membrana Bacteriana Externa/metabolismo , Transporte Biológico/fisiologia , Membrana Celular/metabolismo , Conformação Proteica
17.
Res Microbiol ; 170(8): 338-344, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31376485

RESUMO

The transport of peptides in microorganisms plays an important role in their physiology and behavior, both as a nutrient source and as a proxy to sense their environment. This latter function is evidenced in Gram-positive bacteria where cell-cell communication is mediated by small peptides. Here, we highlight the importance of the oligopeptide permease (Opp) systems in the various major processes controlled by signaling peptides, such as sporulation, virulence and conjugation. We underline that the functioning of these communication systems is tightly linked to the developmental status of the bacteria via the regulation of opp gene expression by transition phase regulators.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Proteínas de Bactérias/metabolismo , Regulação Bacteriana da Expressão Gênica/genética , Bactérias Gram-Positivas/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Transporte Biológico/fisiologia , Fatores de Terminação de Peptídeos/metabolismo , Percepção de Quorum/fisiologia , Transdução de Sinais/fisiologia
18.
Eur J Pharm Biopharm ; 143: 51-60, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31445156

RESUMO

Extensive research has been undertaken to investigate the effect of liposome size in vitro and in vivo. However, it is often difficult to generate liposomes in different size ranges that offer similar low polydispersity and lamellarity. Conventional methods used in the preparation of liposomes, such as lipid film hydration or reverse phase evaporation, generally give rise to liposomal suspensions displaying broad, multimodal size distribution combined with uncontrolled degree of lamellarity. In contrast, microfluidics allows highly homogeneous liposome dispersions to be produced and adjustment of microfluidic operating parameters (flow rate ratio (FRR) and total flow rate (TFR)) can offer size-tuning of liposomes (up to 300 nm, depending on the formulation). Herein, we demonstrate a novel method which allows the production of highly monodisperse, cationic liposomes over a wide particle size range (up to 750 nm in size). This is achieved through controlling the concentration of the aqueous buffer during production. Using this method, liposomes composed of 1,2-dioleoyl-sn-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or dimethyldioctadecylammonium (DDA) - DOPE:DOTAP and DOPE:DDA liposomes - of up to 750 nm were prepared and investigated. These investigations demonstrate that the in vitro cellular uptake of small (40 nm) and large (>500 nm) liposomes in bone marrow-derived macrophages (BMDM) is similar terms of percentage of liposome+ cells and mean fluorescence intensity (MFI). However, significant differences are observed in BMDM uptake when represented in terms of number of liposomes, liposome surface area or liposome internal volume. In vivo biodistribution studies in mice show that by creating small (<50 nm) liposomes we can modify the clearance rates of these liposomes from the injection site and increase accumulation to the draining lymphatics.


Assuntos
Cátions/química , Cátions/metabolismo , Lipossomas Unilamelares/química , Lipossomas Unilamelares/metabolismo , Animais , Transporte Biológico/fisiologia , Química Farmacêutica/métodos , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Microfluídica/métodos , Tamanho da Partícula , Compostos de Amônio Quaternário/química , Distribuição Tecidual/fisiologia
19.
PLoS Biol ; 17(7): e3000363, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31318874

RESUMO

For many years, double-layer phospholipid membrane vesicles, released by most cells, were not considered to be of biological significance. This stance has dramatically changed with the recognition of extracellular vesicles (EVs) as carriers of biologically active molecules that can traffic to local or distant targets and execute defined biological functions. The dimensionality of the field has expanded with the appreciation of diverse types of EVs and the complexity of vesicle biogenesis, cargo loading, release pathways, targeting mechanisms, and vesicle processing. With the expanded interest in the field and the accelerated rate of publications on EV structure and function in diverse biomedical fields, it has become difficult to distinguish between well-established biological features of EV and the untested hypotheses or speculative assumptions that await experimental proof. With the growing interest despite the limited evidence, we sought in this essay to formulate a set of unsolved mysteries in the field, sort out established data from fascinating hypotheses, and formulate several challenging questions that must be answered for the field to advance.


Assuntos
Comunicação Celular/fisiologia , Membrana Celular/metabolismo , Vesículas Extracelulares/metabolismo , Modelos Biológicos , Animais , Transporte Biológico/fisiologia , Endocitose/fisiologia , Exocitose/fisiologia , Vesículas Extracelulares/classificação , Humanos , Tamanho da Partícula
20.
Fluids Barriers CNS ; 16(1): 23, 2019 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-31299984

RESUMO

In our work, "Analysis of Convective and Diffusive Transport in the Brain Interstitium", published in this journal (2019, 16:6), we estimate the interstitial superficial velocity by comparison of transport model simulations to published experimental Real-Time Iontophoresis (RTI) data. In the Discussion section, we calculate a value for perfusion rate, or volumetric flow rate per unit mass of tissue, from these fundamental results of superficial velocity. Drs. Hladky and Barrand have proposed an alternative method for choosing the surface area per volume used to calculate perfusion rate from superficial velocity, using our model domain. Their method seems reasonable to us, as does ours. Upon reflection, a range of volumetric flow per unit mass values should have been reported in our paper, 1-40 µL/min-g. The value calculated using Drs. Hladky and Barrand surface area is a likely upper-bound on this range and the value in the paper is a low estimate at the bottom of the range. We are confident in the estimates of interstitial velocity reported in our article, using the assumptions of the model. Peclet (Pe) numbers, which compare convective and diffusive transport rates for different molecules, were calculated using the superficial velocity estimates; and we continue to believe these values are correct along with all other major results and conclusions presented in the paper.


Assuntos
Encéfalo/metabolismo , Espaço Extracelular/metabolismo , Substância Cinzenta/metabolismo , Transporte Biológico/fisiologia , Difusão , Humanos
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA