title: Glycogen synthase isoforms in Synechocystis sp. PCC6803: identification of different roles to produce glycogen by targeted mutagenesis.
abstract: Synechocystis sp. PCC6803 belongs to cyanobacteria which carry out photosynthesis and has recently become of interest due to the evolutionary link between bacteria and plant species. Similar to other bacteria, the primary carbohydrate storage source of Synechocystis sp. PCC6803 is glycogen. While most bacteria are not known to have any isoforms of glycogen synthase, analysis of the genomic DNA sequence of Synechocystis sp. PCC6803 predicts that this strain encodes two isoforms of glycogen synthase (GS) for synthesizing glycogen structure. To examine the functions of the putative GS genes, each gene (sll1393 or sll0945) was disrupted by double cross-over homologous recombination. Zymogram analysis of the two GS disruption mutants allowed the identification of a protein band corresponding to each GS isoform. Results showed that two GS isoforms (GSI and GSII) are present in Synechocystis sp. PCC6803, and both are involved in glycogen biosynthesis with different elongation properties: GSI is processive and GSII is distributive. Total GS activities in the mutant strains were not affected and were compensated by the remaining isoform. Analysis of the branch-structure of glycogen revealed that the sll1393- mutant (GSI-) produced glycogen containing more intermediate-length chains (DP 8-18) at the expense of shorter and longer chains compared with the wild-type strain. The sll0945- mutant (GSII-) produced glycogen similar to the wild-type, with only a slightly higher proportion of short chains (DP 4-11). The current study suggests that GS isoforms in Synechocystis sp. PCC6803 have different elongation specificities in the biosynthesis of glycogen, combined with ADP-glucose pyrophosphorylase and glycogen branching enzyme.
authors.affiliation: Department of Food Science & Technology and Carbohydrate Bioproduct Research Center, Sejong University, Seoul, Korea.
authors.forename: Sang-Ho
authors.initials: SH
authors.lastname: Yoo
authors.affiliation: Whistler Center for Carbohydrate Research and Department of Food Science, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Byung-Hoo
authors.initials: BH
authors.lastname: Lee
authors.affiliation: Department of Botany, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Youyoun
authors.initials: Y
authors.lastname: Moon
authors.affiliation: Department of Botany, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Martin H
authors.initials: MH
authors.lastname: Spalding
authors.affiliation: Department of Food Science and Human Nutrition, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Jay-Lin
authors.initials: JL
authors.lastname: Jane
mesh_terms: D004789:Enzyme Activation; D017353:Gene Deletion; D006003:Glycogen / Q000096:biosynthesis*; D006006:Glycogen Synthase / Q000235:genetics* / Q000378:metabolism*; D007527:Isoenzymes; D016297:Mutagenesis, Site-Directed; D046939:Synechocystis / Q000235:genetics* / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D006003:Glycogen; D006006:Glycogen Synthase