title: Identification of a novel starch synthase III from the picoalgae Ostreococcus tauri.
abstract: Hydrosoluble glycogen is the major energy storage compound in bacteria, archaea, fungi, and animal cells. In contrast, photosynthetic eukaryotes have evolved to build a highly organized semicrystalline granule of starch. Several enzymes are involved in polysaccharide synthesis, among which glycogen or starch synthase catalyze the elongation of the α-1,4-glucan chain. Ostreococcus tauri, accumulates a single starch granule and contains three starch synthase III (SSIII) isoforms, known as OsttaSSIII-A, OsttaSSIII-B and OsttaSSIII-C. After amino acids sequence analysis we found that OsttaSSIII-C lacks starch-binding domains, being 49% identical to the catalytic region of the SSIII from Arabidopsis thaliana and 32% identical to the entire Escherichia coli glycogen synthase. The recombinant, highly purified OsttaSSIII-C exhibited preference to use as a primer branched glycans (such as rabbit muscle glycogen and amylopectin), rather than amylose. Also, the enzyme displayed a high affinity toward ADP-glucose. We found a marked conservation of the amino acids located in the catalytic site, and specifically determined the role of residues R270, K275 and E352 by site-directed mutagenesis. Results show that these residues are important for OsttaSSIII-C activity, suggesting a strong similarity between the active site of the O. tauri SSIII-C isoform and other bacterial glycogen synthases.
authors.affiliation: Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI-CONICET), Universidad Nacional de Rosario, Suipacha 531, Rosario, 2000, Argentina.
authors.forename: Julieta
authors.initials: J
authors.lastname: Barchiesi
authors.affiliation: Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI-CONICET), Universidad Nacional de Rosario, Suipacha 531, Rosario, 2000, Argentina.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Hedin
authors.affiliation: Laboratorio de Enzimología Molecular, Instituto de Agrobiotecnología del Litoral (UNL-CONICET) & FBCB, Santa Fe, 3000, Argentina.
authors.forename: Alberto A
authors.initials: AA
authors.lastname: Iglesias
authors.affiliation: Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI-CONICET), Universidad Nacional de Rosario, Suipacha 531, Rosario, 2000, Argentina.
authors.forename: Diego F
authors.initials: DF
authors.lastname: Gomez-Casati
authors.affiliation: Department of Chemistry and Biochemistry, Loyola University Chicago, 405 Flanner Hall, 1068 W Sheridan Road, Chicago, IL 60660, USA.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Ballicora
authors.affiliation: Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI-CONICET), Universidad Nacional de Rosario, Suipacha 531, Rosario, 2000, Argentina. Electronic address: busi@cefobi-conicet.gov.ar.
authors.forename: María V
authors.initials: MV
authors.lastname: Busi
mesh_terms: D000688:Amylose / Q000737:chemistry; D000818:Animals; D017360:Arabidopsis / Q000201:enzymology; D002384:Catalysis; D020134:Catalytic Domain; D000460:Chlorophyta / Q000201:enzymology*; D004926:Escherichia coli / Q000201:enzymology; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry / Q000378:metabolism*; D006006:Glycogen Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D020539:Sequence Analysis, Protein; D013214:Starch Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D011134:Polysaccharides; D020033:Protein Isoforms; D006003:Glycogen; D000688:Amylose; D006006:Glycogen Synthase; D013214:Starch Synthase; D005947:Glucose
keywords: O. tauri; Protein activity; Starch synthase