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Membrane Transporters (membrane + transporter)
Selected AbstractsChemInform Abstract: 1,2,3-Triazole-Strapped Calix[4]pyrrole: A New Membrane Transporter for Chloride.CHEMINFORM, Issue 42 2009Matthew G. Fisher Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The uptake by cells of 2-arachidonoylglycerol, an endogenous agonist of cannabinoid receptorsFEBS JOURNAL, Issue 7 2001Tiziana Bisogno It is not yet clear if the endocannabinoid 2-arachidonoylglycerol (2-AG) is transported into cells through the same membrane transporter mediating the uptake of the other endogenous cannabinoid, anandamide (N -arachidonoylethanolamine, AEA), and whether this process (a) is regulated by cells and (b) limits 2-AG pharmacological actions. We have studied simultaneously the facilitated transport of [14C]AEA and [3H]2-AG into rat C6 glioma cells and found uptake mechanisms with different efficacies but similar affinities for the two compounds (Km 11.0 ± 2.0 and 15.3 ± 3.1 µm, Bmax 1.70 ± 0.30 and 0.24 ± 0.04 nmol·min,1·mg protein,1, respectively). Despite these similar Km values, 2-AG inhibits [14C]AEA uptake by cells at concentrations (Ki = 30.1 ± 3.9 µm) significantly higher than those required to either 2-AG or AEA to inhibit [3H]2-AG uptake (Ki = 18.9 ± 1.8 and 20.5 ± 3.2 µm, respectively). Furthermore: (a) if C6 cells are incubated simultaneously with identical concentrations of [14C]AEA and [3H]2-AG, only the uptake of the latter compound is significantly decreased as compared to that observed with [3H]2-AG alone; (b) the uptake of [14C]AEA and [3H]2-AG by cells is inhibited with the same potency by AM404 (Ki = 7.5 ± 0.7 and 10.2 ± 1.7 µm, respectively) and linvanil (Ki = 9.5 ± 0.7 and 6.4 ± 1.2 µm, respectively), two inhibitors of the AEA membrane transporter; (c) nitric oxide (NO) donors enhance the uptake of both [14C]AEA and [3H]2-AG, thus suggesting that 2-AG action can be regulated through NO release; (d) AEA and 2-AG induce a weak release of NO that can be blocked by a CB1 cannabinoid receptor antagonist, and significantly enhanced in the presence of AM404 and linvanil, thus suggesting that transport into C6 cells limits the action of both endocannabinoids. [source] Levodopa treatment reverses endocannabinoid system abnormalities in experimental parkinsonismJOURNAL OF NEUROCHEMISTRY, Issue 4 2003Mauro Maccarrone Abstract Cannabinoid receptors and their endogenous ligands are potent inhibitors of neurotransmitter release in the brain. Here, we show that in a rat model of Parkinson's disease induced by unilateral nigral lesion with 6-hydroxydopamine (6-OHDA), the striatal levels of the endocannabinoid anandamide (AEA) were increased, while the activity of its membrane transporter and hydrolase (fatty-acid amide hydrolase, FAAH) were decreased. These changes were not observed in the cerebellum of the same animals. Moreover, the frequency and amplitude of glutamate-mediated spontaneous excitatory post-synaptic currents were augmented in striatal spiny neurones recorded from parkinsonian rats. Remarkably, the anomalies in the endocannabinoid system, as well as those in glutamatergic activity, were completely reversed by chronic treatment of parkinsonian rats with levodopa, and the pharmacological inhibition of FAAH restored a normal glutamatergic activity in 6-OHDA-lesioned animals. Thus, the increased striatal levels of AEA may reflect a compensatory mechanism trying to counteract the abnormal corticostriatal glutamatergic drive in parkinsonian rats. However, this mechanism seems to be unsuccessful, since spontaneous excitatory activity is still higher in these animals. Taken together, these data show that anomalies in the endocannabinoid system induced by experimental parkinsonism are restricted to the striatum and can be reversed by chronic levodopa treatment, and suggest that inhibition of FAAH might represent a possible target to decrease the abnormal cortical glutamatergic drive in Parkinson's disease. [source] Lipid formulation strategies for enhancing intestinal transport and absorption of P-glycoprotein (P-gp) substrate drugs: In vitro/In vivo case studiesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2007Panayiotis P. Constantinides Abstract The intestinal efflux pump, P-glycoprotein (P-gp), located in the apical membranes of intestinal absorptive cells, can reduce the bioavailability of a wide range of drugs which are substrates for this membrane transporter. In addition to anticancer and anti-HIV drugs, NCEs for other disease indications are P-gp substrates and there is considerable interest in inhibiting P-gp and thus increasing the bioavailability of these molecules. In this review article, an overview of P-gp and its role in drug transport and absorption will be presented first and then formulation strategies to effectively inhibit P-gp will be discussed and compared. These strategies independently and in combination, are: (a) coadministration of another P-gp substrate/specific inhibitor, and (b) incorporation of a nonspecific lipid and/or polymer excipient in the formulation. The first approach, although very effective in inhibiting P-gp, utilizes a second active compound in the formulation and thus imposes regulatory constraints and long development timelines on such combination products. Excipient inhibitors appear to have minimal nonspecific pharmacological activity and thus potential side effects of specific active compound inhibitors can be avoided. Case studies will be presented where specific active compounds, surfactants, polymers, and formulations incorporating these molecules are shown to significantly improve the intestinal absorption of poorly soluble and absorbed drugs as a result of P-gp inhibition and enhanced drug transport in vitro. ©2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:235,248, 2007 [source] Functional specialization and differential regulation of short-chain carboxylic acid transporters in the pathogen Candida albicansMOLECULAR MICROBIOLOGY, Issue 6 2010Neide Vieira Summary The major fungal pathogen Candida albicans has the metabolic flexibility to assimilate a wide range of nutrients in its human host. Previous studies have suggested that C. albicans can encounter glucose-poor microenvironments during infection and that the ability to use alternative non-fermentable carbon sources contributes to its virulence. JEN1 encodes a monocarboxylate transporter in C. albicans and we show that its paralogue, JEN2, encodes a novel dicarboxylate plasma membrane transporter, subjected to glucose repression. A strain deleted in both genes lost the ability to transport lactic, malic and succinic acids by a mediated mechanism and it displayed a growth defect on these substrates. Although no significant morphogenetic or virulence defects were found in the double mutant strain, both JEN1 and JEN2 were strongly induced during infection. Jen1-GFP (green fluorescent protein) and Jen2-GFP were upregulated following the phagocytosis of C. albicans cells by neutrophils and macrophages, displaying similar behaviour to an Icl1-GFP fusion. In the murine model of systemic candidiasis approximately 20,25% of C. albicans cells infecting the kidney expressed Jen1-GFP and Jen2-GFP. Our data suggest that Jen1 and Jen2 are expressed in glucose-poor niches within the host, and that these short-chain carboxylic acid transporters may be important in the early stages of infection. [source] Changes in red cell ion transport, reduced intratumoral neovascularization, and some mild motor function abnormalities accompany targeted disruption of the Mouse Kell gene (Kel),AMERICAN JOURNAL OF HEMATOLOGY, Issue 8 2009Xiang Zhu Kell (ECE-3), a highly polymorphic blood group glycoprotein, displays more than 30 antigens that produce allo-antibodies and, on red blood cells (RBCs), is complexed through a single disulfide bond with the integral membrane protein, XK. XK is a putative membrane transporter whose absence results in a late onset form of neuromuscular abnormalities known as the McLeod syndrome. Although Kell glycoprotein is known to be an endothelin-3-converting enzyme, the full extent of its physiological function is unknown. To study the functions of Kell glycoprotein, we undertook targeted disruption of the murine Kel gene by homologous recombination. RBCs from Kel(,/,) mice lacked Kell glycoprotein, Kell/XK complex, and endothelin-3-converting enzyme activity and had reduced levels of XK. XK mRNA levels in spleen, brain, and testis were unchanged. In Kel(,/,) mice RBC Gardos channel activity was increased and the normal enhancement by endothelin-3 was blunted. Analysis of the microvessels of tumors produced from LL2 cells indicated that the central portion of tumors from wild-type mice were populated with many mature blood vessels, but that vessels in tumors from Kel(,/,) mice were fewer and smaller. The absence of Kell glycoprotein mildly affected some motor activities identified by foot splay on the drop tests. The targeted disruption of Kel in mouse enabled us to identify phenotypes that would not be easily detected in humans lacking Kell glycoprotein. In this regard, the Kell knockout mouse provides a good animal model for the study of normal and/or pathophysiological functions of Kell glycoprotein. Am. J. Hematol., 2009. © 2009 Wiley-Liss, Inc. [source] Use of an in-house approach to study the three-dimensional structures of various outer membrane proteins: structure of the alcaligin outer membrane transporter FauA from Bordetella pertussisACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Karl Brillet Bordetella pertussis is the bacterial agent of whooping cough in humans. Under iron-limiting conditions, it produces the siderophore alcaligin. Released to the extracellular environment, alcaligin chelates iron, which is then taken up as a ferric alcaligin complex via the FauA outer membrane transporter. FauA belongs to a family of TonB-dependent outer membrane transporters that function using energy derived from the proton motive force. Using an in-house protocol for membrane-protein expression, purification and crystallization, FauA was crystallized in its apo form together with three other TonB-dependent transporters from different organisms. Here, the protocol used to study FauA is described and its three-dimensional structure determined at 2.3,Å resolution is discussed. [source] Post-translational regulation of EAAT2 function by co-expressed ubiquitin ligase Nedd4-2 is impacted by SGK kinasesJOURNAL OF NEUROCHEMISTRY, Issue 4 2006Christoph Boehmer Abstract The human excitatory amino acid transporter (EAAT)2 is the major glutamate carrier in the mammalian CNS. Defective expression of the transporter results in neuroexcitotoxicity that may contribute to neuronal disorders such as amyotrophic lateral sclerosis (ALS). The serum and glucocorticoid inducible kinase (SGK) 1 is expressed in the brain and is known to interact with the ubiquitin ligase Nedd4-2 to modulate membrane transporters and ion channels. The present study aimed to investigate whether SGK isoforms and the related kinase, protein kinase B (PKB), regulate EAAT2. Expression studies in Xenopus oocytes demonstrated that glutamate-induced inward current (IGLU) was stimulated by co-expression of SGK1, SGK2, SGK3 or PKB. IGLU is virtually abolished by Nedd4-2, an effect abrogated by additional co-expression of either kinase. The kinases diminish the effect through Nedd4-2 phosphorylation without altering Nedd4-2 protein abundance. SGKs increase the transporter maximal velocity without significantly affecting substrate affinity. Similar to glutamate-induced currents, [3H] glutamate uptake and cell surface abundance of the transporter were increased by the SGK isoforms and down-regulated by the ubiquitin ligase Nedd4-2. In conclusion, all three SGK isoforms and PKB increase EAAT2 activity and plasma membrane expression and thus, may participate in the regulation of neuroexcitability. [source] Expression of transketolase-like 1 (TKTL1) and p-Akt correlates with the progression of cervical neoplasiaJOURNAL OF OBSTETRICS AND GYNAECOLOGY RESEARCH (ELECTRONIC), Issue 3 2008Nico Kohrenhagen Abstract Aim:, It is supposed that increased glycolysis is crucial for the energy supply during tumor progression. Unfortunately, the relevance of glycolysis in cervical neoplasia is unknown, but what is certain is the fact that cervical cancer shows a high expression of glucose membrane transporters, which are necessary for glucose uptake as an energy source. Transketolase-like enzyme 1 (TKTL1) and the oncogene p-Akt have been described to play an important role in glycolysis during tumorigenesis. Thus, we were interested in their expression in cervical tissue. Methods:, We examined the expression of TKTL1 and p-Akt in 80 formalin-fixed, paraffin-embedded cervical specimens: 20 benign cervical tissues, 20 low-grade squamous intraepithelial lesions, 20 high-grade intraepithelial lesions, and 20 invasive squamous cell carcinomas (ISCC). Results:, Immunhistochemical analyses revealed that the intensity of the expression of TKTL1 and p-Akt increases significantly with an increase in the histopathological grade of cervical tissues. Conclusion:, The results suggest that both TKTL1 and p-Akt play an important role in the progression of cervical neoplasia, which may be due to their impact on glycolysis. [source] Genetic analysis of Escherichia coli K1 gastrointestinal colonizationMOLECULAR MICROBIOLOGY, Issue 6 2000J. Martindale Strains of Escherichia coli expressing the K1 polysaccharide capsule colonize the large intestine of newborn infants, and are the leading cause of Gram-negative septicaemia and meningitis in the neonatal period. We used signature-tagged mutagenesis (STM) to identify genes that E. coli K1 requires to colonize the gastrointestinal (GI) tract. A total of 2140 mTn5 mutants was screened for their capacity to colonize the GI tract of infant rats, and 16 colonization defective mutants were identified. The mutants have transposon insertions in genes affecting the synthesis of cell surface structures, membrane transporters, transcriptional regulators, enzymes in metabolic pathways, and in genes of unknown function, designated dgc (defective in GI colonization). Three dgcs are absent from the whole genome sequence of E. coli K-12, although related sequences are found in other pathogenic strains of E. coli and in Shigella flexneri. Additionally, immunohistochemistry was used to define the nature of the colonization defect in five mutants including all dgc mutants. STM was successfully applied to examine the factors involved in E. coli K1 colonization, and the findings are relevant to the pathogenesis of other enteric infections. [source] Structural conservation in the major facilitator superfamily as revealed by comparative modelingPROTEIN SCIENCE, Issue 7 2004Eyal Vardy Abstract The structures of membrane transporters are still mostly unsolved. Only recently, the first two high-resolution structures of transporters of the major facilitator superfamily (MFS) were published. Despite the low sequence similarity of the two proteins involved, lactose permease and glycerol-3-phosphate transporter, the reported structures are highly similar. This leads to the hypothesis that all members of the MFS share a similar structure, regardless of their low sequence identity. To test this hypothesis, we generated models of two other members of the MFS, the Tn10-encoded metal-tetracycline/H+ antiporter (TetAB) and the rat vesicular monoamine transporter (rVMAT2). The models are based on the two MFS structures and on experimental data. The models for both proteins are in good agreement with the data available and support the notion of a shared fold for all MFS proteins. [source] Pseudomonas putida KT2440 responds specifically to chlorophenoxy herbicides and their initial metabolitesPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 11 2006Dirk Benndorf Dr. Abstract Pseudomonas putida,KT2440 is often used as a model to investigate toxicity mechanisms and adaptation to hazardous chemicals in bacteria. The objective of this paper was to test the impact of the chlorophenoxy herbicides 2,4-dichlorophenoxyacetic acid,(2,4-D) and 2-(2,4-dichlorophenoxy)propanoic acid,(DCPP) and their metabolites 2,4-dichlorophenol,(DCP) and 3,5-dichlorocatechol,(DCC), on protein expression patterns and physiological parameters. Both approaches showed that DCC has a different mode of action and induces different responses than DCPP, 2,4-D and DCP. DCC was the most toxic compound and was active as an uncoupler of oxidative phosphorylation. It repressed the synthesis of ferric uptake regulator (Fur)-dependent proteins, e.g. fumarase,C and L -ornithine N5-oxygenase, which are involved in oxidative stress response and iron uptake. DCPP, 2,4-D and DCP were less toxic than DCC. They disturbed oxidative phosphorylation to a lesser extent by a yet unknown mechanism. Furthermore, they repressed enzymes of energy-consuming biosynthetic pathways and induced membrane transporters for organic substrates. A TolC homologue component of multidrug resistance transporters was found to be induced, which is probably involved in the removal of lipophilic compounds from membranes. [source] A comparative proteomic evaluation of culture grown vs nodule isolated Bradyrhizobium japonicumPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 10 2006Annamraju D. Sarma Abstract Total protein extract of Bradyrhizobium japonicum cultivated in HM media were resolved by 2-D PAGE using narrow range IPG strips. More than 1200,proteins were detected, of which nearly 500,proteins were analysed by MALDI-TOF and 310,spots were tentatively identified. The present study describes at the proteome level a significant number of metabolic pathways related to important cellular events in free-living B.,japonicum. A comparative analysis of proteomes of free-living and nodule residing bacteria revealed major differences and similarities between the two states. Proteins related to fatty acid, nucleic acid and cell surface synthesis were significantly higher in cultured cells. Nitrogen metabolism was more pronounced in bacteroids whereas carbon metabolism was similar in both states. Relative percentage of proteins related to global functions like protein synthesis, maturation & degradation and membrane transporters were similar in both forms, however, different proteins provided these functions in the two states. [source] Estrone/17,-estradiol conversion to, and tumor necrosis factor inhibition by, estrogen metabolites in synovial cells of patients with rheumatoid arthritis and patients with osteoarthritisARTHRITIS & RHEUMATISM, Issue 10 2009Martin Schmidt Objective The role of estrogens in rheumatoid arthritis (RA) is debated since both proinflammatory and antiinflammatory effects have been reported. Important evidence of the dual role of estrogens is conversion to various proinflammatory or antiinflammatory metabolites. This study was undertaken to examine the downstream conversion of estrogens in synovial cells from patients with RA or osteoarthritis (OA). Methods We studied serum levels of estrone, estrone sulfate, and estrone sulfate membrane transporters, intracellular interconversion of estrone and 17,-estradiol, and conversion of estrone/17,-estradiol to various estrogen metabolites in RA and OA synovial cells. The effect of estrogen metabolites on tumor necrosis factor (TNF) secretion was also studied in RA and OA synovial cells. Results Serum levels of estrone sulfate were similar in healthy controls and RA patients. Estrone sulfate transporters were present in synovial tissue. Interconversion of estrone and 17,-estradiol and the expression of converting enzymes of the cytochrome P450 family were similar in RA and OA cells. Using estrone and 17,-estradiol as substrates, RA and OA synovial cells produced 16,-, 4-, and 2-hydroxylated estrogens and their 4- and 2-methylation products. The levels of 16,-hydroxylated estrone/17,-estradiol (16,OH-estrone/16,OH-17,-estradiol) were higher than the levels of all other estrogen metabolites. RA synovial cells produced more 16,OH-estrone than did OA synovial cells. Importantly, the 16,OH estrogens did not inhibit TNF secretion, whereas all other estrogen metabolites had marked inhibitory effects. Conclusion Our findings indicate that precursor estrogens are converted to proinflammatory metabolites, particularly in RA synovial cells. RA synovial cells mainly produce the proproliferative 16,OH-estrone, which, in addition to 16,OH-17,-estradiol, is one of the only 2 estrogens studied that does not inhibit TNF secretion. A preponderance of 16,-hydroxylated estrogens is an unfavorable sign in synovial inflammation. [source] Use of an in-house approach to study the three-dimensional structures of various outer membrane proteins: structure of the alcaligin outer membrane transporter FauA from Bordetella pertussisACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Karl Brillet Bordetella pertussis is the bacterial agent of whooping cough in humans. Under iron-limiting conditions, it produces the siderophore alcaligin. Released to the extracellular environment, alcaligin chelates iron, which is then taken up as a ferric alcaligin complex via the FauA outer membrane transporter. FauA belongs to a family of TonB-dependent outer membrane transporters that function using energy derived from the proton motive force. Using an in-house protocol for membrane-protein expression, purification and crystallization, FauA was crystallized in its apo form together with three other TonB-dependent transporters from different organisms. Here, the protocol used to study FauA is described and its three-dimensional structure determined at 2.3,Å resolution is discussed. [source] Crystallization and preliminary X-ray analysis of a C-terminal TonB fragment from Escherichia coliACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2004Jiri Koedding The TonB protein located in the cell wall of Gram-negative bacteria mediates the proton motive force from the cytoplasmic membrane to specific outer membrane transporters. A C-terminal fragment of TonB from Escherichia coli consisting of amino-acid residues 147,239 (TonB-92) has been purified and crystallized. Crystals grew in space group P21 to dimensions of about 1.0 × 0.12 × 0.12,mm. A native data set has been obtained to 1.09,Å resolution. [source] Crystallization and preliminary X-ray crystallographic analysis of MacA from Actinobacillus actinomycetemcomitansACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2008Shunfu Piao Periplasmic membrane-fusion proteins (MFPs) are an essential component of the multidrug efflux pump in Gram-negative bacteria. They play a crucial role in bridging the outer membrane porin TolC and two distinct types of inner membrane transporters. The MFP MacA bridges the inner membrane ABC-type multidrug transporter MacB and the outer membrane porin TolC. MacA from the pathogenic bacterium Actinobacillus actinomycetemcomitans was expressed in Escherichia coli B834 (DE3) and the recombinant protein was purified using Ni,NTA affinity, Q anion-exchange and gel-filtration chromatography. The purified MacA protein was crystallized using the vapour-diffusion method. A MAD diffraction data set was collected to a resolution of 3.0,Å at 100,K. The crystal belongs to space group P622, with unit-cell parameters a = b = 109.2, c = 255.4,Å, , = , = 90, , = 120°, and contains one molecule in the asymmetric unit. [source] Neurotransmitter transporters and their impact on the development of psychopharmacologyBRITISH JOURNAL OF PHARMACOLOGY, Issue S1 2006Leslie Iversen The synaptic actions of most neurotransmitters are inactivated by reuptake into the nerve terminals from which they are released, or by uptake into adjacent cells. A family of more than 20 transporter proteins is involved. In addition to the plasma membrane transporters, vesicular transporters in the membranes of neurotransmitter storage vesicles are responsible for maintaining vesicle stores and facilitating exocytotic neurotransmitter release. The cell membrane monoamine transporters are important targets for CNS drugs. The transporters for noradrenaline and serotonin are key targets for antidepressant drugs. Both noradrenaline-selective and serotonin-selective reuptake inhibitors are effective against major depression and a range of other psychiatric illnesses. As the newer drugs are safer in overdose than the first-generation tricyclic antidepressants, their use has greatly expanded. The dopamine transporter (DAT) is a key target for amphetamine and methylphenidate, used in the treatment of attention deficit hyperactivity disorder. Psychostimulant drugs of abuse (amphetamines and cocaine) also target DAT. The amino-acid neurotransmitters are inactivated by other families of neurotransmitter transporters, mainly located on astrocytes and other non-neural cells. Although there are many different transporters involved (four for GABA; two for glycine/D -serine; five for L -glutamate), pharmacology is less well developed in this area. So far, only one new amino-acid transporter-related drug has become available: the GABA uptake inhibitor tiagabine as a novel antiepileptic agent. British Journal of Pharmacology (2006) 147, S82,S88. doi:10.1038/sj.bjp.0706428 [source] Paramagnetic Liposomes as Innovative Contrast Agents for Magnetic Resonance (MR) Molecular Imaging ApplicationsCHEMISTRY & BIODIVERSITY, Issue 10 2008Enzo Terreno Abstract This article illustrates some innovative applications of liposomes loaded with paramagnetic lanthanide-based complexes in MR molecular imaging field. When a relatively high amount of a GdIII chelate is encapsulated in the vesicle, the nanosystem can simultaneously affect both the longitudinal (R1) and the transverse (R2) relaxation rate of the bulk H2O H-atoms, and this finding can be exploited to design improved thermosensitive liposomes whose MRI response is not longer dependent on the concentration of the probe. The observation that the liposome compartmentalization of a paramagnetic LnIII complex induce a significant R2 enhancement, primarily caused by magnetic susceptibility effects, prompted us to test the potential of such agents in cell-targeting MR experiments. The results obtained indicated that these nanoprobes may have a great potential for the MR visualization of cellular targets (like the glutamine membrane transporters) overexpressing in tumor cells. Liposomes loaded with paramagnetic complexes acting as NMR shift reagents have been recently proposed as highly sensitive CEST MRI agents. The main peculiarity of CEST probes is to allow the MR visualization of different agents present in the same region of interest, and this article provides an illustrative example of the in vivo potential of liposome-based CEST agents. [source] | ||||||||||||||||||||||||||||