title: Two Arabidopsis ADP-glucose pyrophosphorylase large subunits (APL1 and APL2) are catalytic.
abstract: ADP-glucose (Glc) pyrophosphorylase (ADP-Glc PPase) catalyzes the first committed step in starch biosynthesis. Higher plant ADP-Glc PPase is a heterotetramer (alpha(2)beta(2)) consisting of two small and two large subunits. There is increasing evidence that suggests that catalytic and regulatory properties of the enzyme from higher plants result from the synergy of both types of subunits. In Arabidopsis (Arabidopsis thaliana), two genes encode small subunits (APS1 and APS2) and four large subunits (APL1-APL4). Here, we show that in Arabidopsis, APL1 and APL2, besides their regulatory role, have catalytic activity. Heterotetramers formed by combinations of a noncatalytic APS1 and the four large subunits showed that APL1 and APL2 exhibited ADP-Glc PPase activity with distinctive sensitivities to the allosteric activator (3-phosphoglycerate). Mutation of the Glc-1-P binding site of Arabidopsis and potato (Solanum tuberosum) isoforms confirmed these observations. To determine the relevance of these activities in planta, a T-DNA mutant of APS1 (aps1) was characterized. aps1 is starchless, lacks ADP-Glc PPase activity, APS1 mRNA, and APS1 protein, and is late flowering in long days. Transgenic lines of the aps1 mutant, expressing an inactivated form of APS1, recovered the wild-type phenotype, indicating that APL1 and APL2 have catalytic activity and may contribute to ADP-Glc synthesis in planta.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la Cartuja, Universidad de Sevilla-CSIC, 41092-Sevilla, Spain.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Ventriglia
authors.forename: Misty L
authors.initials: ML
authors.lastname: Kuhn
authors.forename: Ma Teresa
authors.initials: MT
authors.lastname: Ruiz
authors.forename: Marina
authors.initials: M
authors.lastname: Ribeiro-Pedro
authors.forename: Federico
authors.initials: F
authors.lastname: Valverde
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Ballicora
authors.forename: Jack
authors.initials: J
authors.lastname: Preiss
authors.forename: José M
authors.initials: JM
authors.lastname: Romero
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D020134:Catalytic Domain; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D013213:Starch / Q000096:biosynthesis
chemical_list: D013213:Starch; D051599:Glucose-1-Phosphate Adenylyltransferase