Glycogen Synthase Isoforms in Synechocystis sp. PCC6803: Identification of Different Roles to Produce Glycogen by Targeted Mutagenesis

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Yoo, Sang-Ho
Lee, Byung-Hoo
Moon, Youyoun
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Jane, Jay-Lin
Distinguished Professor Emeritus
Spalding, Martin
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Food Science and Human Nutrition

The Department of Food Science and Human Nutrition (FSHN) at Iowa State University is jointly administered by the Colleges of Agriculture and Life Sciences and Human Science. FSHN combines the study and practical application of food sciences and technology with human nutrition in preparation for a variety of fields including: the culinary sciences, dietetics, nutrition, food industries, and diet and exercise.

The department was established in 1991 through the merging of the Department of Food Sciences and Technology (of the College of Agriculture), and the Department of Food and Nutrition (of the College of Family and Consumer Sciences).

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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.


This is an article published as Yoo S-H, Lee B-H, Moon Y, Spalding MH, Jane J-l (2014) Glycogen Synthase Isoforms in Synechocystis sp. PCC6803: Identification of Different Roles to Produce Glycogen by Targeted Mutagenesis. PLoS ONE 9(3): e91524. doi:10.1371/journal.pone.0091524. Posted with permission.

Wed Jan 01 00:00:00 UTC 2014