The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform
Philip Cohen - One of the best experts on this subject based on the ideXlab platform.
-
Glycogen synthase kinase 3 from rabbit skeletal muscle
FEBS Journal, 2005Co-Authors: Noor Embi, Dennis B Rylatt, Philip CohenAbstract:Publisher Summary This chapter discusses Glycogen synthase kinase-3 from rabbit skeletal muscle. Glycogen synthase kinase-3 is one of the five Glycogen synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of Glycogen synthase in vivo. It catalyzes the phosphorylation of three serine residues on Glycogen synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing Glycogen synthase through phosphocellulose.
-
inhibition of Glycogen synthase kinase 3 by insulin mediated by protein kinase b
Nature, 1995Co-Authors: Darren Cross, Dario R Alessi, Philip Cohen, Mirjana Andjelkovich, Brian A HemmingsAbstract:Glycogen synthase kinase-3 (GSK3)1 is implicated in the regulation of several physiological processes, including the control of Glycogen2 and protein3 synthesis by insulin, modulation of the transcription factors AP-1 and CREB4–6, the specification of cell fate in Drosophila7 and dorsoventral patterning in Xenopus embryos8. GSK3 is inhibited by serine phosphorylation in response to insulin or growth factors3,9–11 and in vitro by either MAP kinase-activated protein (MAPKAP) kinase-1 (also known as p90rsk) or p70 ribosomal S6 kinase (p70S6k)12,13. Here we show, however, that agents which prevent the activation of both MAPKAP kinase-1 and p70S6k by insulin in vivo do not block the phosphorylation and inhibition of GSK3. Another insulin-stimulated protein kinase inactivates GSK3 under these conditions, and we demonstrate that it is the product of the proto-oncogene protein kinase B (PKB, also known as Akt/RAC). Like the inhibition of GSK3 (refs 10, 14), the activation of PKB is prevented by inhibitors of phosphatidylinositol (PI) 3-kinase.
Peter J Roach - One of the best experts on this subject based on the ideXlab platform.
-
lafora disease offers a unique window into neuronal Glycogen metabolism
Journal of Biological Chemistry, 2018Co-Authors: Matthew S Gentry, Joan J Guinovart, Berge A Minassian, Peter J Roach, Jose M SerratosaAbstract:Lafora disease (LD) is a fatal, autosomal recessive, Glycogen-storage disorder that manifests as severe epilepsy. LD results from mutations in the gene encoding either the Glycogen phosphatase laforin or the E3 ubiquitin ligase malin. Individuals with LD develop cytoplasmic, aberrant Glycogen inclusions in nearly all tissues that more closely resemble plant starch than human Glycogen. This Minireview discusses the unique window into Glycogen metabolism that LD research offers. It also highlights recent discoveries, including that Glycogen contains covalently bound phosphate and that neurons synthesize Glycogen and express both Glycogen synthase and Glycogen phosphorylase.
-
Protein targeting to Glycogen is a master regulator of Glycogen synthesis in astrocytes.
IBRO Reports, 2016Co-Authors: E. Ruchti, Peter J Roach, Anna A. Depaoli-roach, Pierre J. Magistretti, Igor AllamanAbstract:Abstract The storage and use of Glycogen, the main energy reserve in the brain, is a metabolic feature of astrocytes. Glycogen synthesis is regulated by Protein Targeting to Glycogen (PTG), a member of specific Glycogen-binding subunits of protein phosphatase-1 (PPP1). It positively regulates Glycogen synthesis through de-phosphorylation of both Glycogen synthase (activation) and Glycogen phosphorylase (inactivation). In cultured astrocytes, PTG mRNA levels were previously shown to be enhanced by the neurotransmitter noradrenaline. To achieve further insight into the role of PTG in the regulation of astrocytic Glycogen, its levels of expression were manipulated in primary cultures of mouse cortical astrocytes using adenovirus-mediated overexpression of tagged-PTG or siRNA to downregulate its expression. Infection of astrocytes with adenovirus led to a strong increase in PTG expression and was associated with massive Glycogen accumulation (>100 fold), demonstrating that increased PTG expression is sufficient to induce Glycogen synthesis and accumulation. In contrast, siRNA-mediated downregulation of PTG resulted in a 2-fold decrease in Glycogen levels. Interestingly, PTG downregulation strongly impaired long-term astrocytic Glycogen synthesis induced by insulin or noradrenaline. Finally, these effects of PTG downregulation on Glycogen metabolism could also be observed in cultured astrocytes isolated from PTG-KO mice. Collectively, these observations point to a major role of PTG in the regulation of Glycogen synthesis in astrocytes and indicate that conditions leading to changes in PTG expression will directly impact Glycogen levels in this cell type.
-
Incorporation of phosphate into Glycogen by Glycogen synthase.
Archives of Biochemistry and Biophysics, 2016Co-Authors: Christopher J. Contreras, Anna A. Depaoli-roach, Thomas D Hurley, Dyann M. Segvich, Krishna K. Mahalingan, Vimbai M. Chikwana, Terence L. Kirley, Peter J RoachAbstract:Abstract The storage polymer Glycogen normally contains small amounts of covalently attached phosphate as phosphomonoesters at C2, C3 and C6 atoms of glucose residues. In the absence of the laforin phosphatase, as in the rare childhood epilepsy Lafora disease, the phosphorylation level is elevated and is associated with abnormal Glycogen structure that contributes to the pathology. Laforin therefore likely functions in vivo as a Glycogen phosphatase. The mechanism of Glycogen phosphorylation is less well-understood. We have reported that Glycogen synthase incorporates phosphate into Glycogen via a rare side reaction in which glucose-phosphate rather than glucose is transferred to a growing polyglucose chain (Tagliabracci et al. (2011) Cell Metab 13 , 274–282). We proposed a mechanism to account for phosphorylation at C2 and possibly at C3. Our results have since been challenged (Nitschke et al. (2013) Cell Metab 17 , 756–767). Here we extend the evidence supporting our conclusion, validating the assay used for the detection of Glycogen phosphorylation, measurement of the transfer of 32 P from [β- 32 P]UDP-glucose to Glycogen by Glycogen synthase. The 32 P associated with the Glycogen fraction was stable to ethanol precipitation, SDS-PAGE and gel filtration on Sephadex G50. The 32 P-signal was not affected by inclusion of excess unlabeled UDP before analysis or by treatment with a UDPase, arguing against the signal being due to contaminating [β- 32 P]UDP generated in the reaction. Furthermore, [ 32 P]UDP did not bind non-covalently to Glycogen. The 32 P associated with Glycogen was released by laforin treatment, suggesting that it was present as a phosphomonoester. The conclusion is that Glycogen synthase can mediate the introduction of phosphate into Glycogen, thereby providing a possible mechanism for C2, and perhaps C3, phosphorylation.
-
Glycogen and its metabolism some new developments and old themes
Biochemical Journal, 2012Co-Authors: Peter J Roach, Anna A Depaoliroach, Thomas D Hurley, Vincent S TagliabracciAbstract:Glycogen is a branched polymer of glucose that acts as a store of energy in times of nutritional sufficiency for utilization in times of need. Its metabolism has been the subject of extensive investigation and much is known about its regulation by hormones such as insulin, glucagon and adrenaline (epinephrine). There has been debate over the relative importance of allosteric compared with covalent control of the key biosynthetic enzyme, Glycogen synthase, as well as the relative importance of glucose entry into cells compared with Glycogen synthase regulation in determining Glycogen accumulation. Significant new developments in eukaryotic Glycogen metabolism over the last decade or so include: (i) three-dimensional structures of the biosynthetic enzymes Glycogenin and Glycogen synthase, with associated implications for mechanism and control; (ii) analyses of several genetically engineered mice with altered Glycogen metabolism that shed light on the mechanism of control; (iii) greater appreciation of the spatial aspects of Glycogen metabolism, including more focus on the lysosomal degradation of Glycogen; and (iv) Glycogen phosphorylation and advances in the study of Lafora disease, which is emerging as a Glycogen storage disease.
-
Multiple Glycogen-binding Sites in Eukaryotic Glycogen Synthase Are Required for High Catalytic Efficiency toward Glycogen
Journal of Biological Chemistry, 2011Co-Authors: Sulochanadevi Baskaran, Peter J Roach, Wayne A. Wilson, Keri D. Davisk.d. Davis, Anna A. Depaoli-roach, Christopher J. Contreras, Vimbai M. Chikwana, Thomas D HurleyAbstract:Glycogen synthase is a rate-limiting enzyme in the biosynthesis of Glycogen and has an essential role in glucose homeostasis. The three-dimensional structures of yeast Glycogen synthase (Gsy2p) complexed with maltooctaose identified four conserved maltodextrin-binding sites distributed across the surface of the enzyme. Site-1 is positioned on the N-terminal domain, site-2 and site-3 are present on the C-terminal domain, and site-4 is located in an interdomain cleft adjacent to the active site. Mutation of these surface sites decreased Glycogen binding and catalytic efficiency toward Glycogen. Mutations within site-1 and site-2 reduced the Vmax/S0.5 for Glycogen by 40- and 70-fold, respectively. Combined mutation of site-1 and site-2 decreased the Vmax/S0.5 for Glycogen by >3000-fold. Consistent with the in vitro data, Glycogen accumulation in Glycogen synthase-deficient yeast cells (Δgsy1-gsy2) transformed with the site-1, site-2, combined site-1/site-2, or site-4 mutant form of Gsy2p was decreased by up to 40-fold. In contrast to the Glycogen results, the ability to utilize maltooctaose as an in vitro substrate was unaffected in the site-2 mutant, moderately affected in the site-1 mutant, and almost completely abolished in the site-4 mutant. These data show that the ability to utilize maltooctaose as a substrate can be independent of the ability to utilize Glycogen. Our data support the hypothesis that site-1 and site-2 provide a “toehold mechanism,” keeping Glycogen synthase tightly associated with the Glycogen particle, whereas site-4 is more closely associated with positioning of the nonreducing end during catalysis.
Noor Embi - One of the best experts on this subject based on the ideXlab platform.
-
Glycogen synthase kinase 3 from rabbit skeletal muscle
FEBS Journal, 2005Co-Authors: Noor Embi, Dennis B Rylatt, Philip CohenAbstract:Publisher Summary This chapter discusses Glycogen synthase kinase-3 from rabbit skeletal muscle. Glycogen synthase kinase-3 is one of the five Glycogen synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of Glycogen synthase in vivo. It catalyzes the phosphorylation of three serine residues on Glycogen synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing Glycogen synthase through phosphocellulose.
Brian A Hemmings - One of the best experts on this subject based on the ideXlab platform.
-
inhibition of Glycogen synthase kinase 3 by insulin mediated by protein kinase b
Nature, 1995Co-Authors: Darren Cross, Dario R Alessi, Philip Cohen, Mirjana Andjelkovich, Brian A HemmingsAbstract:Glycogen synthase kinase-3 (GSK3)1 is implicated in the regulation of several physiological processes, including the control of Glycogen2 and protein3 synthesis by insulin, modulation of the transcription factors AP-1 and CREB4–6, the specification of cell fate in Drosophila7 and dorsoventral patterning in Xenopus embryos8. GSK3 is inhibited by serine phosphorylation in response to insulin or growth factors3,9–11 and in vitro by either MAP kinase-activated protein (MAPKAP) kinase-1 (also known as p90rsk) or p70 ribosomal S6 kinase (p70S6k)12,13. Here we show, however, that agents which prevent the activation of both MAPKAP kinase-1 and p70S6k by insulin in vivo do not block the phosphorylation and inhibition of GSK3. Another insulin-stimulated protein kinase inactivates GSK3 under these conditions, and we demonstrate that it is the product of the proto-oncogene protein kinase B (PKB, also known as Akt/RAC). Like the inhibition of GSK3 (refs 10, 14), the activation of PKB is prevented by inhibitors of phosphatidylinositol (PI) 3-kinase.
Dennis B Rylatt - One of the best experts on this subject based on the ideXlab platform.
-
Glycogen synthase kinase 3 from rabbit skeletal muscle
FEBS Journal, 2005Co-Authors: Noor Embi, Dennis B Rylatt, Philip CohenAbstract:Publisher Summary This chapter discusses Glycogen synthase kinase-3 from rabbit skeletal muscle. Glycogen synthase kinase-3 is one of the five Glycogen synthase kinases that are identified in skeletal muscle, and is of major importance in determining the kinetic properties of Glycogen synthase in vivo. It catalyzes the phosphorylation of three serine residues on Glycogen synthase, converting the enzyme from a form that is almost fully active in the absence of glucose-6P, to one that is largely dependent on this allosteric activator. Glycogen synthase kinase-3 also has a second activity that is not shared by any other protein kinase—namely, the ability to activate an enzyme termed the MgATP-dependent protein phosphatase. Glycogen synthase may also contain traces of a modified form of phosphorylase kinase that has lost its sensitivity to regulation by calcium ions, and is therefore, no longer inhibited by ethylene glycol tetraacetic acid (EGTA). This is largely removed by passing Glycogen synthase through phosphocellulose.
