Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.4.1.18 (branching enzyme)
628 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Arbuscular mycorrhizal (AM) fungi take up photosynthetically fixed carbon from plant roots and translocate it to their external mycelium. Previous experiments have shown that fungal lipid synthesized from carbohydrate in the root is one form of exported carbon. In this study, an analysis of the labeling in storage and structural carbohydrates after (13)C(1) glucose was provided to AM roots shows that this is not the only pathway for the flow of carbon from the intraradical to the extraradical mycelium (ERM). Labeling patterns in glycogen, chitin, and trehalose during the development of the symbiosis are consistent with a significant flux of exported glycogen. The identification, among expressed genes, of putative sequences for glycogen synthase, glycogen branching enzyme, chitin synthase, and for the first enzyme in chitin synthesis (glutamine fructose-6-phosphate aminotransferase) is reported. The results of quantifying glycogen synthase gene expression within mycorrhizal roots, germinating spores, and ERM are consistent with labeling observations using (13)C-labeled acetate and glycerol, both of which indicate that glycogen is synthesized by the fungus in germinating spores and during symbiosis. Implications of the labeling analyses and gene sequences for the regulation of carbohydrate metabolism are discussed, and a 4-fold role for glycogen in the AM symbiosis is proposed: sequestration of hexose taken from the host, long-term storage in spores, translocation from intraradical mycelium to ERM, and buffering of intracellular hexose levels throughout the life cycle.
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PMID:Carbon export from arbuscular mycorrhizal roots involves the translocation of carbohydrate as well as lipid. 1264 99

Glycogen, a branched polymer of glucose, serves as an energy reserve in many organisms. The degree of branching likely reflects the balance between the activities of glycogen synthase and branching enzyme. Mice overexpressing constitutively active glycogen synthase in skeletal muscle (GSL30) have elevated muscle glycogen. To test whether excess glycogen synthase activity affected glycogen branching, we examined the glycogen from skeletal muscle of GSL30 mice. The absorption spectrum of muscle glycogen determined in the presence of iodine was shifted to higher wavelengths in the GSL30 animals, consistent with a decrease in the degree of branching. As judged by Western blotting, the levels of glycogenin and the branching enzyme were also elevated. Branching enzyme activity also increased approximately threefold. However, this compared with an increase in glycogen synthase of some 50-fold, so that the increase in branching enzyme in response to overexpression of glycogen synthase was insufficient to synthesize normally branched glycogen.
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PMID:Overexpression of glycogen synthase in mouse muscle results in less branched glycogen. 1276 5

Glycogen is a branched polymer of glucose, synthesized as a reserve of both energy and carbon. The branched nature of glycogen is important for its function and polyglucosan bodies, particles that contain a glycogen-like polymer with reduced branching, are a feature of several disease states. The degree of glycogen branching is thought to be governed by the balance between glycogen synthesis and branching activities. However, there have been reports that the intrinsic properties of individual branching enzymes govern the degree of branching. To address the relationship between synthesis and branching more fully, we made use of the yeast Saccharomyces cerevisiae. The glycogen content of yeast cells was manipulated by using different growth conditions or by the introduction of specific mutations. Whenever glycogen storage was elevated, the polysaccharide formed was found to be less branched but normal branching could be restored by overexpression of branching enzyme.
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PMID:Increased glycogen storage in yeast results in less branched glycogen. 1521 44

Osmoregulated periplasmic glucans (OPGs) G protein (OpgG) is required for OPGs biosynthesis. OPGs from Escherichia coli are branched glucans, with a backbone of beta-1,2 glucose units and with branches attached by beta-1,6 linkages. In Proteobacteria, OPGs are involved in osmoprotection, biofilm formation, virulence and resistance to antibiotics. Despite their important biological implications, enzymes synthesizing OPGs are poorly characterized. Here, we report the 2.5 A crystal structure of OpgG from E.coli. The structure was solved using a selenemethionine derivative of OpgG and the multiple anomalous diffraction method (MAD). The protein is composed of two beta-sandwich domains connected by one turn of 3(10) helix. The N-terminal domain (residues 22-388) displays a 25-stranded beta-sandwich fold found in several carbohydrate-related proteins. It exhibits a large cleft comprising many aromatic and acidic residues. This putative binding site shares some similarities with enzymes such as galactose mutarotase and glucodextranase, suggesting a potential catalytic role for this domain in OPG synthesis. On the other hand, the C-terminal domain (residues 401-512) has a seven-stranded immunoglobulin-like beta-sandwich fold, found in many proteins where it is mainly implicated in interactions with other molecules. The structural data suggest that OpgG is an OPG branching enzyme in which the catalytic activity is located in the large N-terminal domain and controlled via the smaller C-terminal domain.
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PMID:Structural analysis of Escherichia coli OpgG, a protein required for the biosynthesis of osmoregulated periplasmic glucans. 1531 17

This study reports the identification of a new class of cassava (Manihot esculenta Crantz) with a storage root showing unusual free sugar accumulation and novel starch. Twenty-seven clones high in free sugar were identified under cultivation in primitive rural community areas in the Amazon. Iodine test and glucose oxidase-peroxidase reagent strips were used, in the field, for identification of starch and glucose, respectively. Five out of these 27 clones of cassava were cultivated at EMBRAPA Genetic Resources and Biotechnology and used for biochemical characterization, starch synthesis enzyme activities and gene expression analysis. Carbohydrates were fractioned into free sugar, polymerized water-soluble and -insoluble alpha-polyglucan. Clones of series CAS36 accumulate over 100 times more free sugar (mainly glucose) than commercial varieties. Monosaccharide composition analysis revealed one clone with distinct water-soluble sugars not present in the commercial cultivar. Structure analysis of the water-soluble and -insoluble alpha-polyglucan revealed the presence of a glycogen-like starch in clone CAS36.1. This clone indicated disruption in the starch synthesis pathway for enzyme activities and protein blot analyses in ADPG-pyrophosphorylase and branching enzyme, and their corresponding protein. Gene expression analysis indicated the lack of transcript for the gene coding for branching enzyme, but not for the gene coding for the ADPG-pyrophosphorylase small subunit. In addition, the pattern of distribution of sugar and starch content showed to be related to tissue age in the storage root.
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PMID:Identification and characterization of a novel cassava (Manihot esculenta Crantz) clone with high free sugar content and novel starch. 1563 Jun 25

The initiation of glycogen synthesis requires the protein glycogenin, which incorporates glucose residues through a self-glucosylation reaction, and then acts as substrate for chain elongation by glycogen synthase and branching enzyme. Numerous sequences of glycogenin-like proteins are available in the databases but the enzymes from mammalian skeletal muscle and from Saccharomyces cerevisiae are the best characterized. We report the isolation of a cDNA from the fungus Neurospora crassa, which encodes a protein, GNN, which has properties characteristic of glycogenin. The protein is one of the largest glycogenins but shares several conserved domains common to other family members. Recombinant GNN produced in Escherichia coli was able to incorporate glucose in a self-glucosylation reaction, to trans-glucosylate exogenous substrates, and to act as substrate for chain elongation by glycogen synthase. Recombinant protein was sensitive to C-terminal proteolysis, leading to stable species of around 31kDa, which maintained all functional properties. The role of GNN as an initiator of glycogen metabolism was confirmed by its ability to complement the glycogen deficiency of a S. cerevisiae strain (glg1 glg2) lacking glycogenin and unable to accumulate glycogen. Disruption of the gnn gene of N. crassa by repeat induced point mutation (RIP) resulted in a strain that was unable to synthesize glycogen, even though the glycogen synthase activity was unchanged. Northern blot analysis showed that the gnn gene was induced during vegetative growth and was repressed upon carbon starvation.
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PMID:GNN is a self-glucosylating protein involved in the initiation step of glycogen biosynthesis in Neurospora crassa. 1568 Sep 13

A role for the Escherichia coli glgX gene in bacterial glycogen synthesis and/or degradation has been inferred from the sequence homology between the glgX gene and the genes encoding isoamylase-type debranching enzymes; however, experimental evidence or definition of the role of the gene has been lacking. Construction of E. coli strains with defined deletions in the glgX gene is reported here. The results show that the GlgX gene encodes an isoamylase-type debranching enzyme with high specificity for hydrolysis of chains consisting of three or four glucose residues. This specificity ensures that GlgX does not generate an extensive futile cycle during glycogen synthesis in which chains with more than four glucose residues are transferred by the branching enzyme. Disruption of glgX leads to overproduction of glycogen containing short external chains. These results suggest that the GlgX protein is predominantly involved in glycogen catabolism by selectively debranching the polysaccharide outer chains that were previously recessed by glycogen phosphorylase.
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PMID:Role of the Escherichia coli glgX gene in glycogen metabolism. 1568 11

Lafora progressive myoclonus epilepsy, caused by defective laforin or malin, insidiously present in normal teenagers with cognitive decline, followed by rapidly intractable epilepsy, dementia and death. Pathology reveals neurodegeneration with neurofibrillary tangle formation and Lafora bodies (LBs). LBs are deposits of starch-like polyglucosans, insufficiently branched and hence insoluble glycogen molecules resulting from glycogen synthase (GS) overactivity relative to glycogen branching enzyme activity. We previously made the unexpected observation that laforin, in the absence of which polyglucosans accumulate, specifically binds polyglucosans. This suggested that laforin's role is to detect polyglucosan appearances during glycogen synthesis and to initiate mechanisms to downregulate GS. Glycogen synthase kinase 3 (GSK3) is the principal inhibitor of GS. Dephosphorylation of GSK3 at Ser 9 activates GSK3 to inhibit GS through phosphorylation at multiple sites. Glucose-6-phosphate is a potent allosteric activator of GS. Glucose-6-phosphate levels are high when the amount of glucose increases and its activation of GS overrides any phospho-inhibition. Here, we show that laforin is a GSK3 Ser 9 phosphatase, and therefore capable of inactivating GS through GSK3. We also show that laforin interacts with malin and that malin is an E3 ubiquitin ligase that binds GS. We propose that laforin, in response to appearance of polyglucosans, directs two negative feedback pathways: polyglucosan-laforin-GSK3-GS to inhibit GS activity and polyglucosan-laforin-malin-GS to remove GS through proteasomal degradation.
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PMID:Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy. 1611 20

The intercellular localization of enzymes involved in starch metabolism and the kinetic properties of ADPglucose pyrophosphorylase were studied in mesophyll protoplasts and bundle sheath strands separated by cellulase digestion of Zea mays L. leaves. Activities of starch synthase, branching enzyme, and ADPglucose pyrophosphorylase were higher in the bundle sheath, whereas the degradative enzymes, starch phosphorylase, and amylase were more evenly distributed and slightly higher in the mesophyll. ADPglucose pyrophosphorylase partially purified from the mesophyll and bundle sheath showed similar apparent affinities for Mg(2+), ATP, and glucose-1-phosphate. The pH optimum of the bundle sheath enzyme (7.0-7.8) was lower than that of the mesophyll enzyme (7.8-8.2). The bundle sheath enzyme showed greater activation by 3-phosphoglycerate than did the mesophyll enzyme, and also showed somewhat higher apparent affinity for 3-phosphoglycerate and lower apparent affinity for the inhibitor, orthophosphate. The observed activities of starch metabolism pathway enzymes and the allosteric properties of the ADPglucose pyrophosphorylases appear to favor the synthesis of starch in the bundle sheath while restricting it in the mesophyll.
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PMID:Regulation of Starch Synthesis in the Bundle Sheath and Mesophyll of Zea mays L. : Intercellular Compartmentalization of Enzymes of Starch Metabolism and the Properties of the ADPglucose Pyrophosphorylases. 1666 98

The localization of enzymes involved in the flow of carbon into and out of starch was determined in guard cells of Commelina communis. The guard cell chloroplasts were separated from the rest of the cellular components by a modification of published microfuge methods. The enzymes of interest were then assayed in the supernatant and chloroplast fractions. The chloroplast yield averaged 75% with 10% cytoplasmic contamination. The enzymes involved in starch biosynthesis, ADPglucose pyrophosphorylase, starch synthase, and branching enzyme, are located exclusively in the chloroplast fraction. The enzymes involved in starch degradation show a more complex distribution. Phosphorylase is located in both the supernatant and chloroplast fraction, 50% in each fraction. Most of the amylase and debranching enzyme activity is present in the supernatant (70%) fraction. The majority of the rest of the enzymes involved in the degradation of starch to malate and synthesis of starch from a hexose precursor were also investigated. All of the enzymes were present in the chloroplast except for hexokinase and phosphofructokinase. The inability to assay these enzymes could possibly have been due to the lack of or low activity of the enzymes or to nonoptimal assay conditions.
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PMID:Localization of Carbohydrate Metabolizing Enzymes in Guard Cells of Commelina communis. 1666 2


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