Structures, properties, and biogenesis of starch and cyanobacterial glycogen

Abstract

branch structures between APs of A-and B-type starches resulted in different dispersed molecular densities in dilute solutions. The APs of B-type starches had much longer but fewer branch-chains, which resulted in smaller dispersed molecular densities compared with the A-type APs. Individual glycogen synthases (GSI and II) and glycogen branching enzyme (GBE) of cyanobacterium Synechocystis sp. PCC6803 were insertionally mutagenized by homologous recombination. Branch chain-length distributions of glycogens produced by GSI" and GSII" mutants were different from each other. Prominent increases in intermediate-size chains (DP8-18) were observed in glycogen of the GSI" mutant compared with those of the wild-type and the GSII" mutant. The results indicated that the two GS isoforms had different specificities on glycogen structure. Because of the GBE deficiency, GBE" mutant strain produced less glucan that had negligible branch-linkages and was water-insoluble. The GBE increased overall rate of glycogen biosynthesis in cyanobacterium.