The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Robert Flaumenhaft - One of the best experts on this subject based on the ideXlab platform.
-
Advances in vascular thiol Isomerase function.
Current Opinion in Hematology, 2017Co-Authors: Robert FlaumenhaftAbstract:PURPOSE OF REVIEW The present review will provide an overview of several recent advances in the field of vascular thiol Isomerase function. RECENT FINDINGS The initial observation that protein disulfide Isomerase (PDI) functions in thrombus formation occurred approximately a decade ago. At the time, there was little understanding regarding how PDI or other vascular thiol Isomerases contribute to thrombosis. Although this problem is far from solved, the past few years have seen substantial progress in several areas that will be reviewed in this article. The relationship between PDI structure and its function has been investigated and applied to identify domains of PDI that are critical for thrombus formation. The mechanisms that direct thiol Isomerase storage and release from platelets and endothelium have been studied. New techniques including kinetic-based trapping have identified substrates that vascular thiol Isomerases modify during thrombus formation. Novel inhibitors of thiol Isomerases have been developed that are useful both as tools to interrogate PDI function and as potential therapeutics. Human studies have been conducted to measure circulating PDI in disease states and evaluate the effect of oral administration of a PDI inhibitor on ex-vivo thrombin generation. SUMMARY Current findings indicate that thiol Isomerase-mediated disulfide bond modification in receptors and plasma proteins is an important layer of control of thrombosis and vascular function more generally.
-
Vascular thiol Isomerases.
Blood, 2016Co-Authors: Robert Flaumenhaft, Bruce FurieAbstract:Thiol Isomerases are multifunctional enzymes that influence protein structure via their oxidoreductase, Isomerase, and chaperone activities. These enzymes localize at high concentrations in the endoplasmic reticulum of all eukaryotic cells where they serve an essential function in folding nascent proteins. However, thiol Isomerases can escape endoplasmic retention and be secreted and localized on plasma membranes. Several thiol Isomerases including protein disulfide Isomerase, ERp57, and ERp5 are secreted by and localize to the membranes of platelets and endothelial cells. These vascular thiol Isomerases are released following vessel injury and participate in thrombus formation. Although most of the activities of vascular thiol Isomerases that contribute to thrombus formation are yet to be defined at the molecular level, allosteric disulfide bonds that are modified by thiol Isomerases have been described in substrates such as αIIbβ3, αvβ3, GPIbα, tissue factor, and thrombospondin. Vascular thiol Isomerases also act as redox sensors. They respond to the local redox environment and influence S-nitrosylation of surface proteins on platelets and endothelial cells. Despite our rudimentary understanding of the mechanisms by which thiol Isomerases control vascular function, the clinical utility of targeting them in thrombotic disorders is already being explored in clinical trials.
-
Thiol Isomerases in Thrombus Formation
Circulation Research, 2014Co-Authors: Bruce Furie, Robert FlaumenhaftAbstract:Protein disulfide Isomerase (PDI), ERp5, and ERp57, among perhaps other thiol Isomerases, are important for the initiation of thrombus formation. Using the laser injury thrombosis model in mice to induce in vivo arterial thrombus formation, it was shown that thrombus formation is associated with PDI secretion by platelets, that inhibition of PDI blocked platelet thrombus formation and fibrin generation, and that endothelial cell activation leads to PDI secretion. Similar results using this and other thrombosis models in mice have demonstrated the importance of ERp5 and ERp57 in the initiation of thrombus formation. The integrins, αIIbβ3 and αVβ3, play a key role in this process and interact directly with PDI, ERp5, and ERp57. The mechanism by which thiol Isomerases participate in thrombus generation is being evaluated using trapping mutant forms to identify substrates of thiol Isomerases that participate in the network pathways linking thiol Isomerases, platelet receptor activation, and fibrin generation. PDI as an antithrombotic target is being explored using isoquercetin and quercetin 3-rutinoside, inhibitors of PDI identified by high throughput screening. Regulation of thiol Isomerase expression, analysis of the storage, and secretion of thiol Isomerases and determination of the electron transfer pathway are key issues to understanding this newly discovered mechanism of regulation of the initiation of thrombus formation.
Bruce Furie - One of the best experts on this subject based on the ideXlab platform.
-
Regulatory role of thiol Isomerases in thrombus formation.
Expert Review of Hematology, 2018Co-Authors: Anish V. Sharda, Bruce FurieAbstract:ABSTRACTIntroduction: The protein disulfide Isomerase (PDI) family of thiol Isomerases are intracellular enzymes known to catalyze the oxidation, reduction and isomerization of disulfide bonds duri...
-
Vascular thiol Isomerases.
Blood, 2016Co-Authors: Robert Flaumenhaft, Bruce FurieAbstract:Thiol Isomerases are multifunctional enzymes that influence protein structure via their oxidoreductase, Isomerase, and chaperone activities. These enzymes localize at high concentrations in the endoplasmic reticulum of all eukaryotic cells where they serve an essential function in folding nascent proteins. However, thiol Isomerases can escape endoplasmic retention and be secreted and localized on plasma membranes. Several thiol Isomerases including protein disulfide Isomerase, ERp57, and ERp5 are secreted by and localize to the membranes of platelets and endothelial cells. These vascular thiol Isomerases are released following vessel injury and participate in thrombus formation. Although most of the activities of vascular thiol Isomerases that contribute to thrombus formation are yet to be defined at the molecular level, allosteric disulfide bonds that are modified by thiol Isomerases have been described in substrates such as αIIbβ3, αvβ3, GPIbα, tissue factor, and thrombospondin. Vascular thiol Isomerases also act as redox sensors. They respond to the local redox environment and influence S-nitrosylation of surface proteins on platelets and endothelial cells. Despite our rudimentary understanding of the mechanisms by which thiol Isomerases control vascular function, the clinical utility of targeting them in thrombotic disorders is already being explored in clinical trials.
-
Thiol Isomerases in Thrombus Formation
Circulation Research, 2014Co-Authors: Bruce Furie, Robert FlaumenhaftAbstract:Protein disulfide Isomerase (PDI), ERp5, and ERp57, among perhaps other thiol Isomerases, are important for the initiation of thrombus formation. Using the laser injury thrombosis model in mice to induce in vivo arterial thrombus formation, it was shown that thrombus formation is associated with PDI secretion by platelets, that inhibition of PDI blocked platelet thrombus formation and fibrin generation, and that endothelial cell activation leads to PDI secretion. Similar results using this and other thrombosis models in mice have demonstrated the importance of ERp5 and ERp57 in the initiation of thrombus formation. The integrins, αIIbβ3 and αVβ3, play a key role in this process and interact directly with PDI, ERp5, and ERp57. The mechanism by which thiol Isomerases participate in thrombus generation is being evaluated using trapping mutant forms to identify substrates of thiol Isomerases that participate in the network pathways linking thiol Isomerases, platelet receptor activation, and fibrin generation. PDI as an antithrombotic target is being explored using isoquercetin and quercetin 3-rutinoside, inhibitors of PDI identified by high throughput screening. Regulation of thiol Isomerase expression, analysis of the storage, and secretion of thiol Isomerases and determination of the electron transfer pathway are key issues to understanding this newly discovered mechanism of regulation of the initiation of thrombus formation.
Soo Jin Yeom - One of the best experts on this subject based on the ideXlab platform.
-
Phosphate sugar Isomerases and their potential for rare sugar bioconversion
Journal of Microbiology, 2020Co-Authors: Soo Jin YeomAbstract:Phosphate sugar Isomerases, catalyzing the isomerization between ketopentose/ketohexose phosphate and aldopentose/aldohexose phosphate, play an important role in microbial sugar metabolism. They are present in a wide range of microorganisms. They have attracted increasing research interest because of their broad substrate specificity and great potential in the enzymatic production of various rare sugars. Here, the enzymatic properties of various phosphate sugar Isomerases are reviewed in terms of their substrate specificities and their applications in the production of valuable rare sugars because of their functions such as low-calorie sweeteners, bulking agents, and pharmaceutical precursor. Specifically, we focused on the industrial applications of D-ribose-5-phosphate Isomerase and D-mannose-6-phosphate Isomerase to produce D-allose and L-ribose, respectively.
-
Development of novel sugar Isomerases by optimization of active sites in phosphosugar Isomerases for monosaccharides.
Applied and Environmental Microbiology, 2012Co-Authors: Soo Jin Yeom, Yeong-su KimAbstract:Phosphosugar Isomerases can catalyze the isomerization of not only phosphosugar but also of monosaccharides, suggesting that the phosphosugar Isomerases can be used as sugar Isomerases that do not exist in nature. Determination of active-site residues of phosphosugar Isomerases, including ribose-5-phosphate Isomerase from Clostridium difficile (CDRPI), mannose-6-phosphate Isomerase from Bacillus subtilis (BSMPI), and glucose-6-phosphate Isomerase from Pyrococcus furiosus (PFGPI), was accomplished by docking of monosaccharides onto the structure models of the Isomerases. The determinant residues, including Arg133 of CDRPI, Arg192 of BSMPI, and Thr85 of PFGPI, were subjected to alanine substitutions and found to act as phosphate-binding sites. R133D of CDRPI, R192 of BSMPI, and T85Q of PFGPI displayed the highest catalytic efficiencies for monosaccharides at each position. These residues exhibited 1.8-, 3.5-, and 4.9-fold higher catalytic efficiencies, respectively, for the monosaccharides than the wild-type enzyme. However, the activities of these 3 variant enzymes for phosphosugars as the original substrates disappeared. Thus, R133D of CDRPI, R192 of BSMPI, and T85Q of PFGPI are no longer phosphosugar Isomerases; instead, they are changed to a d-ribose Isomerase, an l-ribose Isomerase, and an l-talose Isomerase, respectively. In this study, we used substrate-tailored optimization to develop novel sugar Isomerases which are not found in nature based on phosphosugar Isomerases.
-
Overexpression, crystallization and preliminary X-ray crystallographic analysis of D-ribose-5-phosphate Isomerase from Clostridium thermocellum.
Acta crystallographica. Section F Structural biology and crystallization communications, 2009Co-Authors: Junho Jung, Soo Jin Yeom, Jisun Kim, Jin Kwang Kim, Sampath Natarajan, Yeh Jin Ahn, Sang Boem Lim, Lin-woo KangAbstract:Rare sugars are used for many industrial and medical purposes and are produced by the interconversion between aldoses and ketoses catalyzed by sugar and sugar-phosphate Isomerases. Recently, Clostridium thermocellum d-ribose-5-phosphate Isomerase (CTRPI), an aldose-ketose Isomerase, was cloned in order to synthesize d-allose and its substrate specificity was further characterized for industrial usage. CTRPI has a novel substrate specificity that differs from those of other Isomerases, which have broad substrate specificities. CTRPI prefers aldose substrates such as l-talose, d-ribose and d-allose. CTRPI was purified and crystallized in order to determine its three-dimensional structure and thus to elucidate its enzymatic reaction mechanism and understand its substrate specificity. The crystal belonged to the trigonal space group P3(2)21, with unit-cell parameters a = b = 69.5, c = 154.4 angstrom, and diffracted to 1.9 angstrom resolution. According to Matthews coefficient calculations, the crystallographic structure consists of a dimer in the asymmetric unit, with a V(M) of 3.2 angstrom(3) Da(-1) and a solvent content of 61.7%.
Samir Bejar - One of the best experts on this subject based on the ideXlab platform.
-
co expression of l arabinose Isomerase and d glucose Isomerase in e coli and development of an efficient process producing simultaneously d tagatose and d fructose
Enzyme and Microbial Technology, 2007Co-Authors: Moez Rhimi, Mohamed Ali Borgi, Ezzedine Ben Messaoud, Khalifa Ben Khadra, Samir BejarAbstract:Abstract To develop a feasible enzymatic process for the concomitant d -tagatose and d -fructose production, the thermostable l -arabinose Isomerase of Bacillus stearothermophilus US100 ( l -AI US100) and the mutant d -glucose Isomerase obtained from that of Streptomyces SK (SKGI-A103G) were successfully co-expressed in Escherichia coli HB101 strain. The recombinant cells were immobilized in alginate beads and showed, similarly to the free cells, optimal temperatures for d -galactose and d -glucose isomerisation of 80 and 85 °C, respectively. The two Isomerases were optimally active at pH 7.5. Cell entrapment significantly enhanced the acidotolerance of the two Isomerases, as well as their stability at high temperatures. To perform simultaneous isomerisation of d -galactose and d -glucose at 65 °C and pH 7.5 in packed-bed bioreactor, cells concentration, dilution rate, productivity and bioconversion rate were optimized to be 32 g/l, 2.6 h −1 , 3 g/l h and 30%, respectively.
-
Co-expression of l -arabinose Isomerase and d -glucose Isomerase in E. coli and development of an efficient process producing simultaneously d -tagatose and d -fructose
Enzyme and Microbial Technology, 2007Co-Authors: Moez Rhimi, Ezzedine Ben Messaoud, Mohamed Ali Borgi, Khalifa Ben Khadra, Samir BejarAbstract:To develop a feasible enzymatic process for the concomitant D-tagatose and D-fructose production, the thermostable L-arabinose Isomerase of Bacillus stearothermophilus US 100 (L-AI US 100) and the mutant D-glucose Isomerase obtained from that of Streptomyces SK (SKGI-A103G) were successfully co-expressed in Escherichia coli HB101 strain. The recombinant cells were immobilized in alginate beads and showed, similarly to the free cells, optimal temperatures for D-galactose and D-glucose isomerisation of 80 and 85 degrees C, respectively. The two Isomerases were optimally active at pH 7.5. Cell entrapment significantly enhanced the acidotolerance of the two Isomerases, as well as their stability at high temperatures. To perform simultaneous isomerisation of D-galactose and D-glucose at 65 degrees C and pH 7.5 in packed-bed bioreactor, cells concentration, dilution rate, productivity and bioconversion rate were optimized to be 32 g/l, 2.6 h(-1), 3 g/l h and 30%, respectively.
-
Involvement of alanine 103 residue in kinetic and physicochemical properties of glucose Isomerases from Streptomyces species
Biotechnology Journal, 2007Co-Authors: Mohamed Ali Borgi, Moez Rhimi, Samir BejarAbstract:The Ala103 to Gly mutation, introduced within the glucose Isomerase from Streptomyces sp. SK (SKGI) decreased its catalytic efficiency (k(cat)/K(m)) toward D-glucose from 7.1 to 3 mM(-1) min(-1). The reverse counterpart replacement Gly103Ala introduced into the glucose Isomerase of Streptomyces olivochromogenes (SOGI) considerably improved its catalytic efficiency to be 6.7 instead of 3.2 mM(-1) min(-1). This later mutation also increased the half-life time of the enzyme from 70 to 95 min at 80 degrees C and mainly modified its pH profile. These results provide evidence that the residue Ala103 plays an essential role in the kinetic and physicochemical properties of glucose Isomerases from Streptomyces species.
J. G. Zeikus - One of the best experts on this subject based on the ideXlab platform.
-
Purification and characterization of thermostable glucose Isomerase from Clostridium thermosulfurogenes and Thermoanaerobacter strain B6A.
Biochemical Journal, 1991Co-Authors: Chanyong Lee, J. G. ZeikusAbstract:Glucose Isomerases produced by Thermoanaerobacter strain B6A and Clostridium thermosulfurogenes strain 4B were purified 10-11-fold to homogeneity and their physicochemical and catalytic properties were determined. Both purified enzymes displayed very similar properties (native Mr 200,000, tetrameric subunit composition, and apparent pH optima 7.0-7.5). The enzymes were stable at pH 5.5-12.0, and maintained more than 90% activity after incubation at high temperature (85 degrees C) for 1 h in the presence of metal ions. The N-terminal amino acid sequences of both thermostable glucose Isomerases were Met-Asn-Lys-Tyr-Phe-Glu-Asn and were not similar to that of the thermolabile Bacillus subtilis enzyme. The glucose Isomerase from C. thermosulfurogenes and Thermoanaerobacter displayed pI values of 4.9 and 4.8, and their kcat. and Km values for D-glucose at 65 degrees C were 1040 and 1260 min-1 and 140 and 120 mM respectively. Both enzymes displayed higher kcat. and lower Km values for D-xylose than for D-glucose. The C. thermosulfurogenes enzyme required Co2+ or Mg2+ for thermal stability and glucose Isomerase activity, and Mn2+ or these metals for xylose Isomerase activity. Crystals of C. thermosulfurogenes glucose Isomerase were formed at room temperature by the hanging-drop method using 16-18% poly(ethylene glycol) (PEG) 4000 in 0.1 M-citrate buffer.
