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Timothy J Egan - One of the best experts on this subject based on the ideXlab platform.
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Kinetics of b-haematin formation from suspensions of haematin in aqueous benzoic acid
2020Co-Authors: Timothy J Egan, Mmboneni G TshivhaseAbstract:Kinetics of b-haematin (synthetic malaria pigment) formation from haematin have been studied in the presence of aqueous benzoic acid and derivatives of benzoic acid. Formation of the b-haematin product is demonstrated by X-ray diffraction and IR spectroscopy. Reactions were followed by determining the fraction of unreacted haematin at various time points during the process via reaction of extracted aliquots with pyridine. The kinetics can be fitted to the Avrami equation, indicating that the process involves nucleation and growth. Reaction kinetics in stirred benzoic acid are similar to those previously observed in acetic acid, except that benzoic acid is far more active in promoting the reaction than acetic acid. The reaction reaches completion within 2 h in the presence of 0.050 M benzoic acid (pH 4.5, 60 • C). This compares with 1 h in the presence of 4.5 M acetic acid and 4 h in the presence of 2 M acetic acid. The reaction rate in benzoic acid is not affected if the stirring rate is decreased to zero, but very vigorous stirring appears to disrupt nucleation. The rate constant for b-haematin formation in benzoic acid has a linear dependence on benzoic acid concentration and follows Arrhenius behaviour with temperature. There is a bell-shaped dependence on pH. This suggests that the haematin species in which one propionate group is protonated and the other is deprotonated is optimal for b-haematin formation. When the reaction is conducted in para-substituted benzoic acid derivatives, the log of the rate constant increases linearly with the Hammett constant. These findings suggest that the role of the carboxylic acid may be to disrupt hydrogen bonding and p-stacking in haematin, facilitating conversion to b-haematin. The large activation energy for conversion of precipitated haematin to b-haematin suggests that the reaction in vivo most likely involves direct nucleation from solution and probably does not occur in aqueous medium
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hemozoin inhibiting 2 phenylbenzimidazoles active against malaria parasites
European Journal of Medicinal Chemistry, 2018Co-Authors: Fabrizio P Labbate, Roger Hunter, Jill M. Combrinck, Katherine A De Villiers, Ronel Muller, Roxanne Openshaw, Timothy J EganAbstract:Abstract The 2-phenylbenzimidazole scaffold has recently been discovered to inhibit β-Hematin (synthetic hemozoin) formation by high throughput screening. Here, a library of 325,728 N-4-(1H-benzo[d]imidazol-2-yl)aryl)benzamides was enumerated, and Bayesian statistics used to predict β-Hematin and Plasmodium falciparum growth inhibition. Filtering predicted inactives and compounds with negligible aqueous solubility reduced the library to 35,124. Further narrowing to compounds with terminal aryl ring substituents only, reduced the library to 18, 83% of which were found to inhibit β-Hematin formation
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identification and mechanistic evaluation of hemozoin inhibiting triarylimidazoles active against plasmodium falciparum
ACS Medicinal Chemistry Letters, 2017Co-Authors: Kathryn J. Wicht, Roger Hunter, Jill M. Combrinck, Pete Smith, Timothy J EganAbstract:In a previous study, target based screening was carried out for inhibitors of β-Hematin (synthetic hemozoin) formation, and a series of triarylimidazoles were identified as active against Plasmodium falciparum. Here, we report the subsequent synthesis and testing of derivatives with varying substituents on the three phenyl rings for this series. The results indicated that a 2-hydroxy-1,3-dimethoxy substitution pattern on ring A is required for submicromolar parasite activity. In addition, cell-fractionation studies revealed uncommonly large, dose-dependent increases of P. falciparum intracellular exchangeable (free) heme, correlating with decreased parasite survival for β-Hematin inhibiting derivatives.
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Identification and Mechanistic Evaluation of Hemozoin-Inhibiting Triarylimidazoles Active against Plasmodium falciparum
2017Co-Authors: Kathryn J. Wicht, Jill M. Combrinck, Roger Hunter, Peter J. Smith, Timothy J EganAbstract:In a previous study, target based screening was carried out for inhibitors of β-Hematin (synthetic hemozoin) formation, and a series of triarylimidazoles were identified as active against Plasmodium falciparum. Here, we report the subsequent synthesis and testing of derivatives with varying substituents on the three phenyl rings for this series. The results indicated that a 2-hydroxy-1,3-dimethoxy substitution pattern on ring A is required for submicromolar parasite activity. In addition, cell-fractionation studies revealed uncommonly large, dose-dependent increases of P. falciparum intracellular exchangeable (free) heme, correlating with decreased parasite survival for β-Hematin inhibiting derivatives
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Identification and SAR Evaluation of Hemozoin-Inhibiting Benzamides Active against Plasmodium falciparum
Journal of medicinal chemistry, 2016Co-Authors: Kathryn J. Wicht, Roger Hunter, Jill M. Combrinck, Pete Smith, Timothy J EganAbstract:Quinoline antimalarials target hemozoin formation causing a cytotoxic accumulation of ferriprotoporphyrin IX (Fe(III)PPIX). Well-developed SAR models exist for β-Hematin inhibition, parasite activity, and cellular mechanisms for this compound class, but no comparably detailed investigations exist for other hemozoin inhibiting chemotypes. Here, benzamide analogues based on previous HTS hits have been purchased or synthesized. Only derivatives containing an electron deficient aromatic ring and capable of adopting flat conformations, optimal for π–π interactions with Fe(III)PPIX, inhibited β-Hematin formation. The two most potent analogues showed nanomolar parasite activity, with little CQ cross-resistance, low cytotoxicity, and high in vitro microsomal stability. Selected analogues inhibited hemozoin formation in Plasmodium falciparum causing high levels of free heme. In contrast to quinolines, introduction of amine side chains did not lead to benzamide accumulation in the parasite. These data reveal comple...
Jaime Charris - One of the best experts on this subject based on the ideXlab platform.
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synthesis characterization crystal structure and antimalarial activity of 2e 2 1 4 7 chloroquinolin 4 yl amino phenyl ethylidene hydrazine carbothioamide
Orbital: The Electronic Journal of Chemistry, 2017Co-Authors: Yonathan Parra, Gricela Lobo, Jaime Charris, Neira Gamboa De Dominguez, Philip J Rosenthal, Rosa Ferrer, Julia Brunocolmenarez, Jiri GutAbstract:A simple synthesis and study by UV-vis, IR, NMR, ESI-CID-MS 2 and X-ray diffraction of ((2E)-2-(1-{4-[(7-chloroquinolin-4-yl)amino]phenyl}ethylidene)hydrazinecarbothioamide is reported. It was tested in vitro against chloroquine-resistant strain (W2) of Plasmodium falciparum, hemozoin (β-Hematin) formation and cysteine protease falcipain-2. In general, it was found to possess a proved activity in its inhibitory power on the parasite but less active on the formation of hemozoin (β-Hematin) and falcipain-2. Also, the X-ray analysis presented an unexpected electronic density that can be assigned like S(2). This electronic density can be attributed to autocondensation of thiosemicarbazide, generating H 2 S as a subproduct. DOI: http://dx.doi.org/10.17807/orbital.v9i4.1001
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Synthesis, Characterization, Crystal Structure and Antimalarial Activity of (2E)-2-(1-{4-[(7-chloroquinolin-4-yl)amino]phenyl} ethylidene)hydrazine Carbothioamide
Universidade Federal de Mato Grosso do Sul, 2017Co-Authors: Yonathan De Jesus Parra, Gricela Lobo, Jaime Charris, Neira Gamboa De Dominguez, Philip J Rosenthal, Rosa Elena Ferrer, Julia Bruno-colmenarez, Jiri GutAbstract:A simple synthesis and study by UV-vis, IR, NMR, ESI-CID-MS2 and X-ray diffraction of ((2E)-2-(1-{4-[(7-chloroquinolin-4-yl)amino]phenyl}ethylidene)hydrazinecarbothioamide is reported. It was tested in vitro against chloroquine-resistant strain (W2) of Plasmodium falciparum, hemozoin (β-Hematin) formation and cysteine protease falcipain-2. In general, it was found to possess a proved activity in its inhibitory power on the parasite but less active on the formation of hemozoin (β-Hematin) and falcipain-2. Also, the X-ray analysis presented an unexpected electronic density that can be assigned like S(2). This electronic density can be attributed to autocondensation of thiosemicarbazide, generating H2S as a subproduct. DOI: http://dx.doi.org/10.17807/orbital.v9i4.1001
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synthesis and biological evaluation of benzimidazole 5 carbohydrazide derivatives as antimalarial cytotoxic and antitubercular agents
Bioorganic & Medicinal Chemistry, 2011Co-Authors: Jose Camacho, Arthur Barazarte, Neira Gamboa, Juan Rodrigues, Rosario Rojas, Abraham Vaisberg, Robert H Gilman, Jaime CharrisAbstract:Abstract A series of N′-substituted-2-(5-nitrofuran or 5-nitrothiophen-2-yl)-3 H -benzo[ d ]imidazole-5-carbohydrazide derivatives were synthesized and investigated for their abilities to inhibit β-Hematin formation, hemoglobin hydrolysis and in vivo for their antimalarial efficacy in rodent Plasmodium berghei . Selected analogues were screened for their antitubercular activity against sensitive MTB H 37 Rv and multidrug-resistant MDR-MTB strains, and cytotoxic activity against a panel of human tumor cell lines and two nontumourogenic cell lines. Compounds 3a , 5a , f , 6g were the most promising as inhibitors of β-Hematin formation, however, their effect as inhibitors of hemoglobin hydrolysis were marginal. The most active compounds to emerge from the in vitro and in vivo murine studies were 3a and 6i , suggesting an antimalarial activity via inhibition of β-Hematin formation and are as efficient as chloroquine. The cytotoxic and antitubercular activities of the present compounds were not comparable with those of the standard drugs employed. But, however, compound 5b showed better antitubercular activity compared to rifampin against multidrug-resistant MDR-MTB strains. Compounds 3a , 6i and 5b showed a good safety index.
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Synthesis and antimalarial activity of pyrazolo and pyrimido benzothiazine dioxide derivatives.
European journal of medicinal chemistry, 2008Co-Authors: Arthur Barazarte, Gricela Lobo, Neira Gamboa, Juan Rodrigues, Mario V. Capparelli, Angel Alvarez-larena, Simón E. López, Jaime CharrisAbstract:Abstract A series of phenylsubstituted pyrazolo and pyrimido benzothiazine dioxide derivatives were synthesized and investigated for their abilities to inhibit β-Hematin formation, hemoglobin hydrolysis and in vivo for their antimalarial efficacy in rodent Plasmodium berghei. Compounds 3-amino-7-chloro-9-(2′-methylpheyl)-1,9-dihydro-pyrazolo-[4,3-b]benzothiazine 4,4-dioxide 2b and 2,4-diamino-8-chloro-10H-phenyl-pyrimido-[5,4-b]benzothiazine 5,5-dioxide 3a were the most promising as inhibitors of hemoglobin hydrolysis, however, their effect as inhibitors of β-Hematin formation was marginal, except for compound 3-amino-7-chloro-9-(3′-chlorophenyl)-1,9dihydro-pyrazolo-[4,3-b]benzothiazine 4,4-dioxide 2g. The most active compound to emerge from the in vitro and in vivo murine studies was 2b, suggesting an antimalarial activity via inhibition of hemoglobin hydrolysis, however, not as efficient as chloroquine.
Roger Hunter - One of the best experts on this subject based on the ideXlab platform.
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hemozoin inhibiting 2 phenylbenzimidazoles active against malaria parasites
European Journal of Medicinal Chemistry, 2018Co-Authors: Fabrizio P Labbate, Roger Hunter, Jill M. Combrinck, Katherine A De Villiers, Ronel Muller, Roxanne Openshaw, Timothy J EganAbstract:Abstract The 2-phenylbenzimidazole scaffold has recently been discovered to inhibit β-Hematin (synthetic hemozoin) formation by high throughput screening. Here, a library of 325,728 N-4-(1H-benzo[d]imidazol-2-yl)aryl)benzamides was enumerated, and Bayesian statistics used to predict β-Hematin and Plasmodium falciparum growth inhibition. Filtering predicted inactives and compounds with negligible aqueous solubility reduced the library to 35,124. Further narrowing to compounds with terminal aryl ring substituents only, reduced the library to 18, 83% of which were found to inhibit β-Hematin formation
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identification and mechanistic evaluation of hemozoin inhibiting triarylimidazoles active against plasmodium falciparum
ACS Medicinal Chemistry Letters, 2017Co-Authors: Kathryn J. Wicht, Roger Hunter, Jill M. Combrinck, Pete Smith, Timothy J EganAbstract:In a previous study, target based screening was carried out for inhibitors of β-Hematin (synthetic hemozoin) formation, and a series of triarylimidazoles were identified as active against Plasmodium falciparum. Here, we report the subsequent synthesis and testing of derivatives with varying substituents on the three phenyl rings for this series. The results indicated that a 2-hydroxy-1,3-dimethoxy substitution pattern on ring A is required for submicromolar parasite activity. In addition, cell-fractionation studies revealed uncommonly large, dose-dependent increases of P. falciparum intracellular exchangeable (free) heme, correlating with decreased parasite survival for β-Hematin inhibiting derivatives.
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Identification and Mechanistic Evaluation of Hemozoin-Inhibiting Triarylimidazoles Active against Plasmodium falciparum
2017Co-Authors: Kathryn J. Wicht, Jill M. Combrinck, Roger Hunter, Peter J. Smith, Timothy J EganAbstract:In a previous study, target based screening was carried out for inhibitors of β-Hematin (synthetic hemozoin) formation, and a series of triarylimidazoles were identified as active against Plasmodium falciparum. Here, we report the subsequent synthesis and testing of derivatives with varying substituents on the three phenyl rings for this series. The results indicated that a 2-hydroxy-1,3-dimethoxy substitution pattern on ring A is required for submicromolar parasite activity. In addition, cell-fractionation studies revealed uncommonly large, dose-dependent increases of P. falciparum intracellular exchangeable (free) heme, correlating with decreased parasite survival for β-Hematin inhibiting derivatives
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Identification and SAR Evaluation of Hemozoin-Inhibiting Benzamides Active against Plasmodium falciparum
Journal of medicinal chemistry, 2016Co-Authors: Kathryn J. Wicht, Roger Hunter, Jill M. Combrinck, Pete Smith, Timothy J EganAbstract:Quinoline antimalarials target hemozoin formation causing a cytotoxic accumulation of ferriprotoporphyrin IX (Fe(III)PPIX). Well-developed SAR models exist for β-Hematin inhibition, parasite activity, and cellular mechanisms for this compound class, but no comparably detailed investigations exist for other hemozoin inhibiting chemotypes. Here, benzamide analogues based on previous HTS hits have been purchased or synthesized. Only derivatives containing an electron deficient aromatic ring and capable of adopting flat conformations, optimal for π–π interactions with Fe(III)PPIX, inhibited β-Hematin formation. The two most potent analogues showed nanomolar parasite activity, with little CQ cross-resistance, low cytotoxicity, and high in vitro microsomal stability. Selected analogues inhibited hemozoin formation in Plasmodium falciparum causing high levels of free heme. In contrast to quinolines, introduction of amine side chains did not lead to benzamide accumulation in the parasite. These data reveal comple...
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structure function relationships in aminoquinolines effect of amino and chloro groups on quinoline Hematin complex formation inhibition of β Hematin formation and antiplasmodial activity
Journal of Medicinal Chemistry, 2000Co-Authors: Timothy J Egan, Roger Hunter, Catherine H Kaschula, Helder M Marques, And Ashley Misplon, Jason C WaldenAbstract:Comparison of 19 aminoquinolines supports the hypothesis that chloroquine and related antimalarials act by complexing ferriprotoporphyrin IX (Fe(III)PPIX), inhibiting its conversion to β-Hematin (hemozoin) and hence its detoxification. The study suggests that a basic amino side chain is also essential for antiplasmodial activity. 2- And 4-aminoquinolines are unique in their strong affinity for Fe(III)PPIX, and attachment of side chains to the amino group has relatively little influence on the strength of complex formation. Association with Fe(III)PPIX is necessary, but not sufficient, for inhibiting β-Hematin formation. Presence of a 7-chloro group in the 4-aminoquinoline ring is a requirement for β-Hematin inhibitory activity, and this is also unaffected by side chains attached to the amino group. In turn, β-Hematin inhibitory activity is necessary, but not sufficient, for antiplasmodial activity as the presence of an aminoalkyl group attached to the 4-amino-7-chloroquinoline template is essential for st...
Athar H Chishti - One of the best experts on this subject based on the ideXlab platform.
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dematin and adducin tether sodium hydrogen exchanger nhe1 to erythrocyte membrane cytoskeleton
Blood, 2016Co-Authors: Alicia Rivera, Athar H ChishtiAbstract:Dematin is a critical component of the membrane junctional complex in red blood cells. It tethers the spectrin cytoskeleton proteins to the membrane and its genetic deletion in mice causes dissociation of the spectrin, actin and β-adducin from the membrane resulting in the collapse of the red blood cells (RBCs). As dematin lacks a transmembrane domain, it is still unclear how this critical component of the junctional complex is anchored to the RBC membrane. Our previous studies have shown that the multi-transmembrane glucose transporter-1 (GLUT1) interacts with dematin and β-adducin in human RBCs, suggesting a potential role for GLUT1 in recruiting dematin to the membrane. However, as mouse RBCs do not express a GLUT1 homologue, an equivalent membrane receptor for dematin and/or adducin in mice remains to be determined. Using multiple in vitro and in vivo biochemical assays, here we demonstrate that the ubiquitously expressed plasma membrane Na + /H + exchanger, NHE1 (Slc9a1), is one of the receptors for dematin and β-adducin in mature mouse red blood cells. NHE1 directly interacts with the core domain of dematin. Moreover, the dematin headpiece domain mutant S381E, which binds to the core domain with a higher affinity than the wild type, abolished the biochemical interaction between dematin and NHE1. This observation suggests that NHE1 and dematin headpiece domain compete for the same binding site(s) on the core domain. Furthermore, this finding highlights a molecular mechanism whereby an intermolecular switch of dematin regulates its interaction with NHE1 by phosphorylation. Dematin and β-adducin directly interact with NHE1 at its membrane-proximal cytoplasmic domain, which in turn regulates NHE1 activity in response to growth factor stimuli and intracellular pH alterations. Accordingly,we observed an increased cellular sodium content in erythrocytes of dematin headpiece and adducin double knockout mice (DAKO), suggesting a higher NHE1 activity in DAKO erythrocytes. Unlike GLUT1, NHE1 is expressed in both mouse and human RBCs. Thus, our results provide a novel mechanism for linking NHE1 to membrane skeleton and multiple cell signaling pathways through dematin and adducin (Figure 1). Since NHE1 is one of the major regulators of intracellular pH and hypertonic stress, our findings raise the possibility that the dematin-adducin-NHE1 complex may modulate these functions in RBCs as well as in other cell types with broad impact on the regulation of the actin cytoskeleton and cell migration. Disclosures No relevant conflicts of interest to declare.
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dematin and adducin provide a novel link between the spectrin cytoskeleton and human erythrocyte membrane by directly interacting with glucose transporter 1
Journal of Biological Chemistry, 2008Co-Authors: Anwar A Khan, Toshihiko Hanada, Morvarid Mohseni, Jongjin Jeong, Lixiao Zeng, Massimiliano Gaetani, Brent C Reed, David W Speicher, Athar H ChishtiAbstract:Dematin and adducin are actin-binding proteins located at the spectrin-actin junctions, also called the junctional complex, in the erythrocyte membrane. Here we propose a new model whereby dematin and adducin link the junctional complex to human erythrocyte plasma membrane. Using a combination of surface labeling, immunoprecipitation, and vesicle proteomics approaches, we have identified glucose transporter-1 as the receptor for dematin and adducin in the human erythrocyte membrane. This finding is the first description of a transmembrane protein that binds to dematin and adducin, thus providing a rationale for the attachment of the junctional complex to the lipid bilayer. Because homologues of dematin, adducin, and glucose transporter-1 exist in many non-erythroid cells, we propose that a conserved mechanism may exist that couples sugar and other related transporters to the actin cytoskeleton.
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combined deletion of mouse dematin headpiece and β adducin exerts a novel effect on the spectrin actin junctions leading to erythrocyte fragility and hemolytic anemia
Journal of Biological Chemistry, 2006Co-Authors: Huiqing Chen, Anwar A Khan, Fei Liu, Diana M Gilligan, Luanne L Peters, Joanne B Messick, Wanda M Haschekhock, Agnes E Ostafin, Athar H ChishtiAbstract:Dematin and adducin are actin-binding proteins of the erythrocyte "junctional complex." Individually, they exert modest effects on erythrocyte shape and membrane stability, and their homologues are expressed widely in non-erythroid cells. Here we report generation and characterization of double knock-out mice lacking beta-adducin and the headpiece domain of dematin. The combined mutations result in altered erythrocyte morphology, increased membrane instability, and severe hemolysis. Peripheral blood analysis shows evidence of severe hemolytic anemia with reduced number of erythrocytes/hematocrit/hemoglobin and an approximately 12-fold increase in the number of circulating reticulocytes. The presence of a variety of misshapen and fragmented erythrocytes correlates with increased osmotic fragility and reduced in vivo life span. Despite the apparently normal protein composition of the mutant erythrocyte membrane, the retention of the spectrin-actin complex in the membrane under low ionic strength conditions is significantly reduced by the double mutation. Atomic force microscopy reveals an increase in grain size and a decrease in filament number of the mutant membrane cytoskeleton, although the volume parameter is similar to wild type erythrocytes. Aggregated, disassembled, and irregular features are visualized in the mutant membrane, consistent with the presence of large protein aggregates. Importantly, purified dematin binds to the stripped inside-out vesicles in a saturable manner, and dematin-membrane binding is abolished upon pretreatment of membrane vesicles with trypsin. Together, these results reveal an essential role of dematin and adducin in the maintenance of erythrocyte shape and membrane stability, and they suggest that the dematin-membrane interaction could link the junctional complex to the plasma membrane in erythroid cells.
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combined deletion of mouse dematin headpiece and β adducin exerts a novel effect on the spectrin actin junctions leading to erythrocyte fragility and hemolytic anemia
Journal of Biological Chemistry, 2006Co-Authors: Huiqing Chen, Anwar A Khan, Fei Liu, Diana M Gilligan, Luanne L Peters, Joanne B Messick, Wanda M Haschekhock, Agnes E Ostafin, Athar H ChishtiAbstract:Abstract Dematin and adducin are actin-binding proteins of the erythrocyte “junctional complex.” Individually, they exert modest effects on erythrocyte shape and membrane stability, and their homologues are expressed widely in non-erythroid cells. Here we report generation and characterization of double knock-out mice lacking β-adducin and the headpiece domain of dematin. The combined mutations result in altered erythrocyte morphology, increased membrane instability, and severe hemolysis. Peripheral blood analysis shows evidence of severe hemolytic anemia with reduced number of erythrocytes/hematocrit/hemoglobin and an ∼12-fold increase in the number of circulating reticulocytes. The presence of a variety of misshapen and fragmented erythrocytes correlates with increased osmotic fragility and reduced in vivo life span. Despite the apparently normal protein composition of the mutant erythrocyte membrane, the retention of the spectrin-actin complex in the membrane under low ionic strength conditions is significantly reduced by the double mutation. Atomic force microscopy reveals an increase in grain size and a decrease in filament number of the mutant membrane cytoskeleton, although the volume parameter is similar to wild type erythrocytes. Aggregated, disassembled, and irregular features are visualized in the mutant membrane, consistent with the presence of large protein aggregates. Importantly, purified dematin binds to the stripped inside-out vesicles in a saturable manner, and dematin-membrane binding is abolished upon pretreatment of membrane vesicles with trypsin. Together, these results reveal an essential role of dematin and adducin in the maintenance of erythrocyte shape and membrane stability, and they suggest that the dematin-membrane interaction could link the junctional complex to the plasma membrane in erythroid cells.
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headpiece domain of dematin is required for the stability of the erythrocyte membrane
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Richie Khanna, Alicia Rivera, Seon Hee Chang, Shaida Andrabi, Mohammad Azam, Anthony C Kim, Carlo Brugnara, Philip S Low, Shih Chun Liu, Athar H ChishtiAbstract:Dematin is an actin-binding and bundling protein of the erythrocyte membrane skeleton. Dematin is localized to the spectrin-actin junctions, and its actin-bundling activity is regulated by phosphorylation of cAMP-dependent protein kinase. The carboxyl terminus of dematin is homologous to the "headpiece" domain of villin, an actin-bundling protein of the microvillus cytoskeleton. The headpiece domain contains an actin-binding site, a cAMP-kinase phosphorylation site, plays an essential role in dematin self-assembly, and bundles F-actin in vitro. By using homologous recombination in mouse embryonic stem cells, the headpiece domain of dematin was deleted to evaluate its function in vivo. Dematin headpiece null mice were viable and born at the expected Mendelian ratio. Hematological evaluation revealed evidence of compensated anemia and spherocytosis in the dematin headpiece null mice. The headpiece null erythrocytes were osmotically fragile, and ektacytometry/micropore filtration measurements demonstrated reduced deformability and filterability. In vitro membrane stability measurements indicated significantly greater membrane fragmentation of the dematin headpiece null erythrocytes. Finally, biochemical characterization, including the vesicle/cytoskeleton dissociation, spectrin self-association, and chemical crosslinking measurements, revealed a weakened membrane skeleton evidenced by reduced association of spectrin and actin to the plasma membrane. Together, these results provide evidence for the physiological significance of dematin and demonstrate a role for the headpiece domain in the maintenance of structural integrity and mechanical properties of erythrocytes in vivo.
Jason C Walden - One of the best experts on this subject based on the ideXlab platform.
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structure function relationships in aminoquinolines effect of amino and chloro groups on quinoline Hematin complex formation inhibition of β Hematin formation and antiplasmodial activity
Journal of Medicinal Chemistry, 2000Co-Authors: Timothy J Egan, Roger Hunter, Catherine H Kaschula, Helder M Marques, And Ashley Misplon, Jason C WaldenAbstract:Comparison of 19 aminoquinolines supports the hypothesis that chloroquine and related antimalarials act by complexing ferriprotoporphyrin IX (Fe(III)PPIX), inhibiting its conversion to β-Hematin (hemozoin) and hence its detoxification. The study suggests that a basic amino side chain is also essential for antiplasmodial activity. 2- And 4-aminoquinolines are unique in their strong affinity for Fe(III)PPIX, and attachment of side chains to the amino group has relatively little influence on the strength of complex formation. Association with Fe(III)PPIX is necessary, but not sufficient, for inhibiting β-Hematin formation. Presence of a 7-chloro group in the 4-aminoquinoline ring is a requirement for β-Hematin inhibitory activity, and this is also unaffected by side chains attached to the amino group. In turn, β-Hematin inhibitory activity is necessary, but not sufficient, for antiplasmodial activity as the presence of an aminoalkyl group attached to the 4-amino-7-chloroquinoline template is essential for st...
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structure function relationships in aminoquinolines effect of amino and chloro groups on quinoline Hematin complex formation inhibition of beta Hematin formation and antiplasmodial activity
Journal of Medicinal Chemistry, 2000Co-Authors: Timothy J Egan, Roger Hunter, Catherine H Kaschula, Helder M Marques, And Ashley Misplon, Jason C WaldenAbstract:Comparison of 19 aminoquinolines supports the hypothesis that chloroquine and related antimalarials act by complexing ferriprotoporphyrin IX (Fe(III)PPIX), inhibiting its conversion to beta-Hematin (hemozoin) and hence its detoxification. The study suggests that a basic amino side chain is also essential for antiplasmodial activity. 2- And 4-aminoquinolines are unique in their strong affinity for Fe(III)PPIX, and attachment of side chains to the amino group has relatively little influence on the strength of complex formation. Association with Fe(III)PPIX is necessary, but not sufficient, for inhibiting beta-Hematin formation. Presence of a 7-chloro group in the 4-aminoquinoline ring is a requirement for beta-Hematin inhibitory activity, and this is also unaffected by side chains attached to the amino group. In turn, beta-Hematin inhibitory activity is necessary, but not sufficient, for antiplasmodial activity as the presence of an aminoalkyl group attached to the 4-amino-7-chloroquinoline template is essential for strong activity. We thus propose that the 4-aminoquinoline nucleus of chloroquine and related antimalarials is responsible for complexing Fe(III)PPIX, the 7-chloro group is required for inhibition of beta-Hematin formation, and the basic amino side chain is required for drug accumulation in the food vacuole of the parasite.