title: Functional and structural characterization of the catalytic domain of the starch synthase III from Arabidopsis thaliana.
abstract: Glycogen and starch are the major energy storage compounds in most living organisms. The metabolic pathways leading to their synthesis involve the action of several enzymes, among which glycogen synthase (GS) or starch synthase (SS) catalyze the elongation of the alpha-1,4-glucan backbone. At least five SS isoforms were described in Arabidopsis thaliana; it has been reported that the isoform III (SSIII) has a regulatory function on the synthesis of transient plant starch. The catalytic C-terminal domain of A. thaliana SSIII (SSIII-CD) was cloned and expressed. SSIII-CD fully complements the production of glycogen by an Agrobacterium tumefaciens glycogen synthase null mutant, suggesting that this truncated isoform restores in vivo the novo synthesis of bacterial glycogen. In vitro studies revealed that recombinant SSIII-CD uses with more efficiency rabbit muscle glycogen than amylopectin as primer and display a high apparent affinity for ADP-Glc. Fold class assignment methods followed by homology modeling predict a high global similarity to A. tumefaciens GS showing a fully conservation of the ADP-binding residues. On the other hand, this comparison revealed important divergences of the polysaccharide binding domain between AtGS and SSIII-CD.
authors.affiliation: IIB-INTECH, CONICET-UNSAM, Camino Circunvalación km 6, 7130, Chascomús, Buenos Aires, Argentina.
authors.forename: Maria V
authors.initials: MV
authors.lastname: Busi
authors.forename: Nicolas
authors.initials: N
authors.lastname: Palopoli
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Valdez
authors.forename: Maria S
authors.initials: MS
authors.lastname: Fornasari
authors.forename: Nahuel Z
authors.initials: NZ
authors.lastname: Wayllace
authors.forename: Diego F
authors.initials: DF
authors.lastname: Gomez-Casati
authors.forename: Gustavo
authors.initials: G
authors.lastname: Parisi
authors.forename: Rodolfo A
authors.initials: RA
authors.lastname: Ugalde
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D020134:Catalytic Domain; D003001:Cloning, Molecular; D019295:Computational Biology; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D005964:Glucosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; D005964:Glucosyltransferases; C504530:starch synthase III, Arabidopsis