title: Redox regulation of glycogen biosynthesis in the cyanobacterium Synechocystis sp. PCC 6803: analysis of the AGP and glycogen synthases.
abstract: Glycogen constitutes the major carbon storage source in cyanobacteria, as starch in algae and higher plants. Glycogen and starch synthesis is linked to active photosynthesis and both of them are degraded to glucose in the dark to maintain cell metabolism. Control of glycogen biosynthesis in cyanobacteria could be mediated by the regulation of the enzymes involved in this process, ADP-glucose pyrophosphorylase (AGP) and glycogen synthase, which were identified as putative thioredoxin targets. We have analyzed whether both enzymes were subjected to redox modification using purified recombinant enzymes or cell extracts in the model cyanobacterium Synechocystis sp. PCC 6803. Our results indicate that both AGP and glycogen synthases are sensitive to copper oxidation. However, only AGP exhibits a decrease in its enzymatic activity, which is recovered after reduction by DTT or reduced thioredoxin (TrxA), suggesting a redox control of AGP. In order to elucidate the role in redox control of the cysteine residues present on the AGP sequence (C45, C185, C320, and C337), they were replaced with serine. All AGP mutant proteins remained active when expressed in Synechocystis, although they showed different electrophoretic mobility profiles after copper oxidation, reflecting a complex pattern of cysteines interaction.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Américo Vespucio 49, E-41092 Sevilla, Spain.
authors.forename: Sandra
authors.initials: S
authors.lastname: Díaz-Troya
authors.forename: Luis
authors.initials: L
authors.lastname: López-Maury
authors.forename: Ana María
authors.initials: AM
authors.lastname: Sánchez-Riego
authors.forename: Miguel
authors.initials: M
authors.lastname: Roldán
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Florencio
mesh_terms: D003545:Cysteine / Q000378:metabolism; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000737:chemistry / Q000378:metabolism*; D006003:Glycogen / Q000096:biosynthesis*; D006006:Glycogen Synthase / Q000378:metabolism*; D010084:Oxidation-Reduction; D046939:Synechocystis / Q000201:enzymology / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism
chemical_list: D013879:Thioredoxins; D006003:Glycogen; D006006:Glycogen Synthase; D051599:Glucose-1-Phosphate Adenylyltransferase; D003545:Cysteine
keywords: Synechocystis; cyanobacteria; glycogen; redox regulation.; thioredoxin